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Massive Stars Form Alone

Massive stars have a huge effect on the environment in which they form. Their light dominates the appearance of star forming regions despite their rarity; their stellar winds put a stop to any other star formation that might happen in the area; and when they die, they produce the heavy elements needed for terrestrial planets and life. However, there has long been a debate over how and where they form.

There are two competing models for massive star formation. One model requires massive stars to form in massive clusters with lots of lower mass stars. The other allows massive stars to form nearly alone, in clusters with only a few stars. Determining which of these models is correct is important to understanding the physics behind star formation.

Hubble image of giant starTo determine which model is correct, a group of graduate students ran a set of simulations based on the two different star formation models. They then analyzed a set of relatively isolated massive stars imaged by the Hubble Space Telescope (see image, right), and compared the observations to the models.

What they found is that massive stars do not need to form in massive clusters. Some massive stars may actually form almost alone, in clouds barely more massive than the star. In the words of lead author Joel Lamb, "Our results show that you can, in fact, form big stars in small ponds."

Wide field image of AzV 67There is a possibility that the stars they studied are no long in the area where they formed. Of the eight stars they observed, at least two were clearly runaways. However, several of the others are still surrounded by wisps of gas and dust, indicating that they probably haven't moved since they formed (see image, left).

"Our findings don't support the scenario that the maximum mass of a star in a cluster has to correlate with the size of the cluster," said Prof. Sally Oey.

J. B. Lamb, M. S. Oey, J. K. Werk and L. D. Ingleby published their work in the December 20th edition of the Astrophysical Journal under the title "The Sparsest Clusters With O Stars." It is available at http://iopscience.iop.org/0004-637X/725/2/1886

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Ralph Baldwin dies

Michigan Astronomy Alumnus Ralph Baldwin died Oct. 28 at the age of 98. He will be sorely missed by all in this department.

Dr. Baldwin had several highly successful careers during his long life, including president of Oliver Machinery Company and senior scientist at the Johns Hopkins Applied Physics Laboratory (APL). He earned a Presidential Certificate of Merit for his work on the radio proximity fuse during World War II at APL.

The astronomy community will remember him best for his early recognition that the craters on the Moon are caused by impacts. His first book on the subject, “The Face of the Moon” inspired many scientists, including Nobel laureate Harold Urey. In their biography of Baldwin, the Royal Astronomical Society of Canada states “Seldom has a single book had such far-reaching consequences in the progress of science. Although the scientific community was slow to show interest in his ideas, today Baldwin is regarded with awe because he got so much so right so early!”

This department is indebted to Dr. Baldwin for his generosity. Among his many philanthropic contributions, we can count the Ralph B. Baldwin Professorship in Astronomy, currently held by Hugh Aller, and the Baldwin Prize in Astrophysics and Space Science. The Baldwin Prize is awarded each year to a recent UM Ph.D. in astronomy, astrophysics, or space science for making an original and significant contribution to the field. Sarah Ragan was the 2010 recipient of this award.

The Mystery of the Missing Baryons

Most of the matter in the universe can’t actually be seen. We know it’s there because of the pull of gravity, but it doesn't emit any light, not even at non-visible wavelengths like radio or X-ray, so astronomers call it “Dark Matter.” They call the matter they can observe “baryonic matter.” Baryons are the electrons, protons, and similar particles that make up things like gas, stars, and planets.

Astronomers use satellites like the Wilkinson Microwave Anisotropy Probe to observe the Cosmic Microwave Background, which is the light left over from the Big Bang. From this, astronomers can tell that about 1/6th of the matter in the universe should be baryonic. However, when they look at relatively nearby galaxies, they can only find about half of the baryons they expect. So where are the missing baryons?

Graduate student Michael Anderson and Prof. Joel Bregman are trying to answer that question. They searched through data from more than 100 galaxies looking for the baryons. Discover recently featured their results online, although the study was originally published in March.

Hot galactic haloMany astronomers believe the missing baryons are in the hot, thin gas found around galaxies, called the galactic halo (the blue in the image to the right). Anderson and Bregman examined our own galaxy, the Milky Way, in great detail, and looked at multiple observations of other galaxies. Bregman summarized their results in just a few words: “the matter really isn't there,” he told Discover.

Another possibility is that supernovas or jets from active black holes blew the baryons out of the galaxies. This gave Anderson and Bregman two things to look for. Galaxies with very little gas and many stars likely had more supernovas in the past than galaxies with a lot of gas, so gas-poor galaxies should have fewer baryons. Larger black holes tend to be more active, so galaxies with more massive black holes should have fewer baryons. However, Anderson and Bregman found no correlation between the amount of baryons and the gas in the galaxy or the size of the black hole.

Anderson and Bregman conclude that the simplest explanation is that the baryons never fell into the galaxies in the first place. Instead, they are probably still in the incredibly thin and very hot gas between the galaxies. This gas is so thin, it’s almost impossible to detect, and so hot, it emits almost all its light in x-rays. Designers include observations of this gas and the search for baryons in the mission plans of satellites like the International X-Ray Observatory.

Artist's Concept of the first starsThese results also have important consequences for people studying galaxy formation. The models now have to account for the lack of baryons in galaxies. This study lends support to one popular model of galaxy formation begins with stars hundreds of time more massive that then Sun. Those stars die in enormous supernova explosions, and their cores collapse into large black holes. Some astronomers believe these black holes are the seeds of supermassive black holes around which galaxies form (click the image at left for a story and animation about this.) The supernova explosion would carry away the baryons in the outer layers of the stars, leaving the region where the galaxy forms with fewer baryons.

More observations could confirm the location of the baryons, or the existence of those early, very massive stars. Refined models of galaxy formation will also help, by narrowing the field of what is possible and what observers should look for. But for now, the location of the missing baryons remains a mystery.

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Revealing the Hidden Centers of Forming Stars

L1527 is a small object in the earliest stages of star formation in the constellation of Taurus. It is one of the closest examples of a forming star to us, so it makes a good target for studying the early stages of star formation.

L1527: actual images, original model, refined modelStars form out of clouds of gas and dust, which collapse into a disk. Early on, the gas and dust are so thick that it is hard to make out anything but the outermost edge of the disk. The central object, the proto-star, is almost impossible to see, so astronomers were a bit surprised when they took a picture of L1527 with Spitzer several years ago, and saw a tiny, dim spot of light near the center of the disk.

In 2008, graduate student John Tobin, along with Profs. Lee Hartmann and Nuria Calvet published a model of how this system could be structured, and proposed a set of observations to test their model.

Tobin used the Near-Infrared Imager on the Gemini North telescope to take pictures of L1527 in the infrared and compare those images to his model. Infrared can penetrate the dust more easily that most other forms of light, so this gives astronomers the best chance of peering into the cloud to see what’s inside. Additionally, the Gemini telescope has a very good resolution, so Tobin hoped to be able to make out fine details.

The initial images confirmed the fundamentals of their model. L1527 has a disk surrounding the protostar. The disk is probably highly flared, so it is thin in the center and thick farther out. The bright area in the Spitzer image is a bi-polar cavity carved out of the surrounding gas and dust.

They then refined the model, adding information like the outer radius of the disk. The results were a near perfect match between their model and the image. The image to the right shows the actual images, the first model, and the refined model.

These results imply that the disks where planets develop form very early during the star formation process. They also lend support to the theory of star formation.

These results will be published in a paper called “The Inner Envelope and Disk of L1527 Revealed: Gemini L'-band Scattered Light Imaging” by Tobin, Hartmann, and Loinard in the Astrophysical Journal Letters. It is available at http://arxiv.org/abs/1008.3429v1.

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Testing the formation of Supermassive Black Holes

Super-massive black holes (SMBHs) are black holes thousands or even millions of time more massive than the Sun. Nearly every galaxy in the universe appears to have one in its center. Most galaxy formation models depend on the presence of a SMBH, and there even seems to be a correlation between the size of the SMBH and the size of the galaxy. But where do SMBHs come from? Prof. Marta Volonteri has been pondering that puzzle.

SMBH dwell in most galaxies"Every time you look in a galaxy for a [supermassive] black hole, you find it; and the mass of the black hole is typically a 1,000 times less than the mass of the galaxy.

"How has such a great correlation been established? How is it possible they knew so well about each other throughout these past 13 billion years? So, we really want to know how the black holes started and how they grew with time," Volonteri told BBC News.

There are two proposed theories for how supermassive black holes form. The older idea about is based on our understanding of how stellar-mass black holes form.

When a very massive star dies, the star's core collapses into a black hole. The mass of the black hole depends on the mass of the star: the more massive the star, the bigger its core is, so the bigger the black hole is. In the very early universe, stars were hundreds of times more massive than the Sun, so the black holes they left behind could also be hundreds of times more massive than the Sun. If several of these black holes collide and merge, the result could be a SMBH. In this model, the size of the galaxy determines the size of the SMBH. Galaxies that start out very big have many more very massive stars than small galaxies, so they have many more black holes, which can merge and form a SMBH. The relationship between the size of the black hole and the size of the galaxy should exist even in the very early universe.

Several years ago, Marta Volonteri proposed an alternative theory. She and her colleges proposed that the massive black hole could grow out of the gas at the core of an embryonic galaxy. In this model, the gas at the core of the galaxy collapses and forms a black hole, even while the outer layers are still collapsing. This is the theory tested by a new computer model by Lucio Mayer and his colleges and published in Nature on Aug. 26.

Mayer's model showed that when two massive young galaxies collide and merge, their gas forms one giant, unstable disk. The center of that disk quickly collapses in on itself, forming a black hole millions of time more massive than the Sun. This allows the black hole to grow very quickly to truly supermassive sizes, hundreds of millions of solar masses, in a very short time. The galaxy then grows up around the SMBH. The more massive the SMBH is, the more gas it can hold on to, and the bigger the galaxy becomes.

"If we are right, one expects that [in the early Universe] there will be no clear relation as in the present-day Universe, since the black holes would be already very massive (because they form in only a few hundred thousand years after galaxy collisions) while the galaxies still have to grow a lot until the present time," said Mayer in an interview with the BBC.

There is still gas in the disk after the SMBH forms, which continues to fall in to the black hole. As it falls in, it emits much more light than the rest of the galaxy. The disk is small, at least compared to the rest of the galaxy, so it makes a compact but very bright light at the center of the galaxy. Such a compact and exceptionally bright object is a quasar, and we observe these shining from billions of light years away. This gives astronomers something to look for to test the theory.

"Once this newly born SMBH seed starts to grow, by accreting matter from the dense cloud of gas in which it is embedded, we can hope to spot it as a quasar," writes Volonteri in Nature.

However, there were a couple drawbacks to the simulation. The computer model works best only for very massive galaxies, but SMBHs are found in all sizes of galaxies. This leads to the interesting possibility that both models of SMBH formation could be correct, but the older one based on the remnants of massive stars works for small galaxies, and the newer idea of the formation of a SMBH 'seed' works for large galaxies.

So how will astronomers determine which model is correct? Volonteri ended her article in Nature with the following statement:

"The James Webb Space Telescope (the successor to the Hubble Space Telescope), future X-ray missions such as IXO and the gravitational-wave telescope LISA will all have the technical capabilities to detect quasars and SMBHs in the early Universe. These therefore promise to provide further insight into the process that generates SMBHs 'from scratch'."

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A Speeding Star Raises Questions, and Answers

The location of HE 0437-5439HE 0437-5439 might not sound like a very interesting name, but it is certainly a very interesting star. It is a blue giant about 200,000 light years from us in almost the same direction as the Large Magellanic Cloud See image, left), one of our closest galactic neighbors. The diameter of the galactic disk, where most of the stars reside, is only about 100,000 light years, so HE 0437-5439 is much farther from the center than most of the stars in the galaxy.

It is flying along at about 500 miles per second, one of the fastest stars ever detected, and so fast it will eventually escape our galaxy altogether. Stars moving fast enough to escape the galaxy are called Hyper Velocity Stars, or HVS, and there are only a few of these known to astronomers. At 9 times the mass of the Sun, HE 0437-5439 is by far the most massive HVS known.

The materials that make up HE 0437-5439 are also puzzling. Its composition is similar to stars near core of our galaxy, but it is also similar to stars in the Large Magellanic cloud. This and its position led some astronomers to conclude that it was probably an escapee from the Large Magellanic cloud, not from our own galaxy. HVSs are predicted as a consequence of the massive black hole at the center of our galaxy, so it is important for astronomers to confirm where HVSs originate.

Image of HE 0437-5439 from 2006To answer the questions about the origins of HE 0437-5439, a team of astronomers headed by Prof. Oleg Gnedin used the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. The ACS is designed to take highly detailed and very precise images of faint objects, exactly what the team needed. The team used two images, one from July 2006 (see right), and the other from December 2009. They compared the position of the star relative to distant background galaxies in both images. From the change in position, they determined how fast and in what direction the star moved.

Although the motion is tiny, their results clearly show HE 0437-5439 is headed out of our galaxy and away from the core. "This is the first objective evidence that these hypervelocity stars do come from the center of the galaxy," said Gnedin. The observations eliminated the possibility that this star could have come from another galaxy. However, they opened up a new puzzle.

Stars spend more of their lives fusing hydrogen into helium in their cores. Astronomers graph stars on the Hertzsprung-Russell diagram, and stars fusing hydrogen in their cores fall onto a line called the main sequence, so astronomers simply refer to them as main sequence stars. Blue stars are much hotter than other stars, so they go through their fuel much faster. A blue giant, like HE 0437-5439, should live about 20 million years on the Main Sequence. Based on the analysis of the ACS images, HE 0437-5439 encountered the galactic center about 100 million years ago. So how can it still be a main sequence star?

The team thinks they have the answer to that too.

HVSs get their extreme velocity if they start out as a multiple star system before their encounter with the massive black hole. Anything that goes around the black hole will get a boost, similar to the slingshot or gravity boost we use to speed up spacecraft within the solar system. If what encounters the black hole is a binary system, one of the stars may fall into the black hole. Angular moment must be conserved, so the star that falls into the black hole transfers its angular momentum to the star that escapes, giving it an even bigger boost. However, if the system that encounters the black hole is made of a close binary and a third star much farther out, things get even more interesting. The farther star falls into the black hole, transferring its angular momentum to the close binary pair. The close binary pair then becomes a HVS.

"It's an example of a very violent interaction that happens as a direct consequence of the black hole there.”

But that still leaves a binary, and HE 0437-5439 is a single star. To understand how to get to a single star, we have to look at what happens as close binary systems evolve.

In close binary systems, each star evolves normally while on the main sequence. The more massive star in the pair uses up its hydrogen fuel first, and swells up to become a red giant. The red giant can be so big it may actually engulf the other star. The two stars spiral together, and merge into a single star. This brings a fresh supply of hydrogen to the core of the new star, so it settles back onto the main sequence. This is called a blue straggler, because it appears to be a massive blue star still on the main sequence long after a star its age should have died.

triple system becomes a single HVS

"This star was problematic from the beginning," said Gnedin. "It was the most massive of all the hypervelocity stars we found and therefore it appeared to have the shortest lifetime, about five times shorter than the expected flight time from center of the galaxy to its current position if it was ejected. A solution for that is that it is a blue straggler, a binary system of two stars that were ejected together and merged during flight.

"We had theorized that you could only get such high velocity if you kick a star from very close to a black hole in a special way that involves another star or object. It's a three-body interaction. The black hole rips apart a binary or tertiary star system, captures one of the companions and jettisons the others."

In addition to being a check on our understanding of the Massive Black Hole at the center of the galaxy, astronomers can use HVSs to map the dark matter halo around the galaxy. Dark matter cannot be observed directly. Instead, it is detected through its gravitational interaction with other objects. Mapping the paths of HVSs, especially how they change over several years, reveals the shape of the dark matter halo. Since the HVSs are out in the halo, the biggest effect on their motion is the pull from the dark matter.

According to Gnedin, "[s]tudying these stars could provide more clues about the nature of some of the universe's unseen mass, and it could help astronomers better understand how galaxies form. Dark matter's gravitational pull is measured by the shape of the hyperfast stars' trajectories out of the Milky Way."

This research was published in the Astrophysical Journal letters under the title “A Galactic Center Origin for HE 0437-5439, the Hypervelocity Star near the Large Magellanic Cloud” by Warren R. Brown, Jay Anderson, Oleg Y. Gnedin, Howard E. Bond, Margaret J. Geller, Scott J. Kenyon, and Mario Livio and is available online at http://arxiv.org/abs/1007.3493

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First Observation of Massive Star Formation

For years, astronomers have debated about how massive stars formed. Some believed they formed the same way that smaller stars do, by accumulating mass falling out of a disk of dust and gas. However, stars 10 times more massive than our Sun or larger have strong stellar winds and emit a lot of light, which led some theorists to believe the disk would be blown away before the star could become that big. They believe massive stars must start as smaller stars that merge to form a massive star.

"How these high mass stars form has been a debate for 20 years," said Dr. Stefan Kraus of the University of Michigan, who led a team that set out to end the debate.

IRAS 13481-6124Some smaller stars exhibit jets of material while they are forming. “Such jets are commonly observed around young low-mass stars and generally indicate the presence of a disc," says Kraus. He and his team searched for jets associated with more massive objects in the Spitzer image archive. They found a perfect candidate in IRAS 13481-6124, a young stellar object 18 times more massive than the Sun and about 10,000 light years away in the constellation Centaurus.

IRAS 13481-6124 is surrounded by a large cloud of gas and dust (see image, left.) However, the infrared detectors on the Very Large Telescope Interferometer (VLTI) at the European Southern Observatory (ESO) in Chile is designed to peer inside clouds just like this. An interferometer combines the light from several telescopes to get a sharper, more detailed image.

"With a 10-meter telescope, this star is just a point. With interferometry, we can resolve the disk," said Kraus." We were able to get a very sharp view into the innermost regions around this star, …basically mimicking the resolving power of a telescope with an incredible 85-meter [280-foot] mirror."

Disk around IRAS 13481-6124What they found was a disk of gas and dust very similar to the disks found around smaller stars. "The disk very much resembles what we see around young stars that are much smaller, except everything is scaled up and more massive" said Kraus. “Our observations show that formation works the same for all stars, regardless of mass."

Additionally, the resolution of the VLTI is good enough to rule out the possibility of several young stellar objects in the disk. This appears to rule out the hypothesis that massive stars must form through mergers.

The innermost part of the disk appears to be clear of gas and dust. This leads the team to believe the system is about 60,000 years old. It has finished gaining mass and has only to blow the disk away to be a full-fledged star. “One can say that the baby is about to hatch!"

Future work on this object will focus on the inner region of the disk in order to better determine if the disks really do behave the same way for massive stars. According to Kraus, “…the Atacama Large Millimeter/submillimeter Array (ALMA), currently being constructed in Chile, could provide much information on these inner parts, and allow us to better understand how baby massive stars became heavy."

Understanding massive stars is important because the material needed to build planets like Earth and the heavy elements needed for life are only created when massive stars die in a supernova. "In the future, we might be able to see gaps in this and other dust disks, created by orbiting planets, although it is unlikely that such bodies could survive for long," said Kraus. "A planet around such a massive star would be destroyed by the strong stellar winds and intense radiation as soon as the protective disk material is gone, which leaves little chance for the development of solar systems like our own."

The paper titled "A hot compact dust disk around a massive young stellar object" appears in the July 15 edition of the journal Nature and is available at http://www.nature.com/nature/journal/v466/n7304/full/nature09174.html (login may be required)

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Michigan Astronomy on Big Ten Network

Michigan Astronomy was featured on "Out of the Blue" on the Big Ten Network in June. Episode 211 has a segment on the Detroit Observatory and the history of Astronomy at the University of Michigan, and a segment on modern work in the Department. The show includes interviews with Joel Bregman, Pat Seitzer, and grad student Laura Ingleby, as well as Karen Wight of the Detroit Observatory and history professor Rudi Lindner. Episodes are archived and available for download at http://www.ootb.tv/episodes.html.You can view the Detroit Observatory segment at http://www.ootb.tv/dvd/epi211/Astro1.mov and the department segment at http://www.ootb.tv/dvd/epi211/Astro2.mov.

The Origins of Milky Way Halo Clouds

Like all spiral galaxies, most of the matter in the Milky Way resides in a disk only a few thousand light years thick and around 100,000 light years across. However, a few stars, mostly in globular clusters, and a few clouds of gas reside outside the disk in the region called the halo. Astronomers thought that the number of gas and dust clouds would decline sharply as they looked farther from the disk since the gas should fall into the disk. However, radio observations of the halo indicated there could actually be a number of clouds in the halo.

clouds in the Milky Way HaloWhile she was a PhD student at Swinburne University, Alyson Ford and her advisors, Felix J. Lockman, of the National Radio Astronomy Observatory (NRAO), and Naomi McClure-Griffiths of CSIRO Astronomy and Space Science, used the Parkes Radio Telescope to get a closer look at the halo. Radio telescopes are used to observe the clouds because they are mostly cold hydrogen gas, which only emits light in the radio part of the spectrum. They surveyed about 650 clouds in two regions, one to the north and one to the south of the galactic plane. The clouds were between 400 and 15,000 light years away from the galactic plane. Since the regions were the same size and distance from the disk, they expected the two regions to look the same.

The clouds looked similar in both regions: each cloud is about 600 times more massive than the Sun and is 30 to 40 light years in diameter. However, in the region north of the disk, there were three times more clouds and the clouds were twice as far from the disk than in the southern region. The differences were so large that the team had to start looking for a reason.

The region south of the disk is above an area between two of the spiral arms, where very little is going on. The region north of the disk is above the galactic bar, where the spiral arms connect to the central bulge of the galaxy. It is a region of intense star formation. In star forming regions, there are young stars with strong stellar winds, and very massive stars that live out their whole lives and blow up as supernovas while smaller stars are still in the process of forming.

"We've concluded that these clouds are gas that has been blown away from the Galaxy's plane by supernova explosions and the fierce winds from young stars in areas of intense star formation," said Dr. Ford.

Their findings have important implications for the formation of planets and stars like the sun. Most of the material that makes up terrestrial planets like Earth must form in stars and supernovae. These clouds provide a mechanism to redistribute the heavier materials around the galaxy. The bubbles carry heavy elements into the halo. They gradually fall back to the galactic plane in a new region, where they could become part of a new star and planetary system.

The image and quote were taken from http://www.nrao.edu/pr/2010/haloclouds/.

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UM Grad Student Explores the Formation of Binary Stars

Sirius, a binary star, seen in X-rayMost stars in our galaxy are actually multiple stars, in systems where all the stars orbit around a common center of mass. The most common is a pair of stars called a binary, like Sirius in the image to the left. Astronomers have long wondered how these types of system form: do the stars form independently near each other and fall into orbit around each other, or do they all form together in a single cloud? Most astronomers believe wide binaries form separately and fall into orbit around each other, but they have been less sure about close binaries.

Stars form in giant molecular clouds, which are made of gas and dust. Individual stars, and possibly stellar systems, form inside a tiny, dense piece of the giant molecular cloud called the proto-stellar envelope. When single stars like our Sun form, the envelope is symmetric, so it looks the same on both sides of the proto-star. Graduate student John Tobin and his team were studying some nearby proto-stars when they noticed that many of the proto-stellar envelopes were not symmetrical. Curious about whether or not this was generally true, they looked at some archived Spitzer Space Telescope images. For some of their proto-stars, they also took ground-based images from Kitt Peak, Cerro Tololo Inter-American Observatory, and Magellan.

Protostellar envelope images by J. Tobin

They were able to find 20 proto-stellar envelopes in the Spitzer data where they also had enough other observations to reliably analyze the images. Of these 20, 17 were asymmetric, even blob-like.

"We were really surprised by the prevalence of asymmetrical envelope structures," said Tobin. "And because we know that most stars are binary, these asymmetries could be indicative of how they form."

They also found that the asymmetry was in a very small area, only a few thousand AU across. That's about the size of a typical close binary pair. According to Tobin, "[w]e see asymmetries in the dense material around these proto-stars on scales only a few times larger than the size of the solar system. This means that the disks around them will be fed unevenly, possibly enhancing fragmentation of the disk and triggering binary star formation."

Next, the team compared these observations to models of star formation. They found the best match was to models in which an early asymmetry in the envelope eventually results in two proto-stars forming in the same envelope. If the envelope starts out with some sort of asymmetry, that asymmetry is likely to grow. However, if the disk starts out symmetric, it is very hard to develop an asymmetry that matches the observations. This places constraints on what astronomers need to include in their models. For example, the magnetic field is thought to have a large effect on star formation, but these observations show it has very little effect on the asymmetry of the envelope.

In addition, the team looked at where the proto-stellar envelopes formed. Molecular clouds usually have long "filaments," or strands of denser material. The envelopes in this study were all either located in a bend in the filament, where the different sections may be coming together, or on the edge of the cloud where the cloud could be compressed by an interstellar wind. The shape of the molecular cloud may have an effect on where the stars form and how close together the envelopes form.

The paper "Complex Structure in Class 0 Protostellar Envelopes" by Tobin, John J.; Hartmann, Lee; Looney, Leslie W.; Chiang, Hsin-Fang. appeared in the Astrophysical Journal, Volume 712, Issue 2and is available at http://adsabs.harvard.edu/abs/2010ApJ...712.1010T (login may be required)

Information and quotes for this article were taken from the NASA News story available at http://spitzer.caltech.edu/news/1123-feature10-07-Two-Peas-in-an-Irregular-Pod-How-Binary-Stars-May-Form

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UM Astronomers Part Of Team To Discover "Hole" In Space

A team of astronomers that includes UofM astronomers John Tobin, Edwin Bergin, Nuria Calvet and Lee Hartmann made a surprising discovery recently: a hole in space.

Herschel finds a hole in spaceThe team, which included astronomers from 17 different institutions, combined images from the Herschel space telescope with infra-red images taken at Kitt Peak National Observatory and Atacama Pathfinder Experiment in order to get a better look at a group of very young stars, called proto-stars, in Orion. They got an unprecedented view of the proto-stars, but they also got a big surprise.

Stars form from clouds of gas and dust, so proto-stars should be encased in a cloud of gas and dust. As proto-stars begin to glow, they will push away the cloud, eventually leaving a relatively empty space around the star. Sometimes, the dust around proto-stars can be so thick that it actually blocks the light from everything behind it, so it looks like a dark cloud. Herschel can look into or right through these dark clouds to see what’s inside.

NGC 1999 reflection nebulaIn the past, when astronomers looked at the area labeled NGC 1999, it appeared to be a proto-star with a dark cloud. Herschel should have been able to see the dust glowing. However, when it looked into NGC 1999, it still looked dark. There were only two possible explanations for this: either the dust was so thick that even Herschel couldn't see through it, or it was actually a hole in the gas and dust.

Astronomers took another infrared image using the Magellan telescope in Chile. “We see a couple of background stars shining through the purported dark cloud and a couple of jets shooting out (the green)” said John Tobin. Adding this image to the Herschel observations shows that it really is a bubble of empty space around the proto-star. The jets may have helped clear the hole, along with the radiation from the young stars in the area.

 

Magellan IR image of NGC 1999The Principal Investigator, Tom Megeath of the University of Toledo, Ohio called it “… as surprising as knowing you have worms tunneling under your lawn, but finding one morning that they have created a huge, yawning pit."

Observations such as these show the power of combining images from several observatories, especially combining ground-based and space-based images. This may be just the first step in discovering how stars emerge from their birth clouds.

Information and the quote from Tom Megeath were taken from the NASA/ESA/Herschel press release, available at http://www.nasa.gov/mission_pages/herschel/herschel20100511.html

 

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A Michigan Instrument Solves A Centuries Old Mystery

Nearly two centuries ago, astronomers first noticed that ε Aurigae, the 5th brightest star in the constellation Auriga, changed in brightness, getting dimmer then brighter again. Over the following century, it dimmed and brightened several times. By the end of the 19th century, astronomers knew ε Aurigae was an eclipsing binary with a 27.1-year period.

Artist's conception of Epsilon AurigaeAn eclipsing binary is a system of two stars orbiting each other with orbits aligned with Earth so that one of the stars passes in between us and the other star, blocking the light from the star. These systems are very useful to astronomers, because they can measure the mass and diameter of the stars. By the early 20th century, astronomers knew the two stars in ε Aurigae must be about the same mass, but the diameter was a real puzzle. If both stars had the same mass, they should have about the same brightness, but the companion was much dimmer than the primary star. Additionally, the brightness during eclipse would fluctuate a little, as if what was in front of the primary star was partially transparent.

The most widely accepted model of this system is an evolved giant star and a slightly smaller companion with a disk (see the artist’s conception shown above left.) However, many astronomers still had reservations about adopting it. In order for it to be the right model, everything had to align just right. Not only did the two stars have to align with Earth, but the disk around the companion star also had to align perfectly. The chances of everything aligning so perfectly on a star so nearby are very small. However, an instrument developed here in the Astronomy Department may have solved the puzzle.MIRC

Astronomers used the Michigan Infra-red Combiner (MIRC – pictured right) installed on the CHARA array at Mt. Wilson to image ε Aurigae. MIRC uses interferometry to combine light from four different telescopes to produce extremely high-resolution images. The images (below) show what appears to be a disk passing in front of the star.

“This really shows that the basic paradigm was right, despite the slim probability,” said John Monnier, who developed the MIRC. “It kind of blows my mind that we could capture this. There’s no other system like this known. On top of that, it seems to be in a rare phase of stellar life. And it happens to be so close to us! It’s extremely fortuitous.”Epsilon Aurigae images from 2009 showing the disk occulting the star

In an animation created by putting together several images taken on several different days shows what appears to be a disk moving in front of the primary star. The disk is not as wide as the star, which means it must be very thin. Much thinner in fact than recent spectrographic observations from the Spitzer space Telescope predict. “It’s really flat as a pancake,” Monnier said. (Click here to open the animation in another window)

The research appears in the April 8 2010 edition of Nature in a paper entitled “Infrared images of the transiting disk in the ε Aurigae System.” Graduate student Xiao Che also contributed to the paper.

Information and quotes for this article were taken from the UM News Service story at http://www.ns.umich.edu/htdocs/releases/story.php?id=7621

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HIFI Reveals Organic Molecules in the Orion Nebula

After suffering a malfunction last August, the Heterodyne Instrument for the Far Infrared (HIFI) spectrograph is back up and running, and the results so far are absolutely amazing.

The HIFI spectrum of the Orion NebulaEvery element and molecule has a unique emission spectrum: a specific set of wavelengths of light (“colors” in visible light.) The pattern is always the same for any specific element or molecule. A spectrograph breaks down light into separate wavelengths and measures how many photons it received at each wavelength. A graph of the data from a spectrograph has spikes wherever there are more photons at a particular wavelength. Astronomers can match the pattern of the spikes from an object to patterns from known material to identify what elements or molecules are in the object.

Professor Edwin Bergin is the principle investigator for the HEXOS Key Program on the Herschel Space Observatory, which is a program to use HIFI to study the Orion and Sagittarius star forming regions. Orion was HIFI’s first target in January.

Astronomers are particularly interested in Orion because it is one of the closest areas to us where active star formation is happening. By taking the spectrum, astronomers can determine what atoms and molecules are present when the star and its planets form. This leads to an understanding of what materials are present on the surface of planets early in their history, which may help in determining how life began.

It is a long process to try and match all the different patterns, but so far astronomers have identified water, carbon monoxide, formaldehyde, methanol, dimethyl ether, hydrogen cyanide, sulfur oxide, and sulfur dioxide, as well as several or their isotopes. None of these come as a surprise since they have all been identified before in the Orion region. However, they have barely begun the analysis, and they expect to find many more, possibly even new organic molecules. The detail and sensitivity from HIFI is far greater than any other instrument they've worked with.

Prof. Bergin summed it up this way: "This HIFI spectrum, and the many more to come, will provide a virtual treasure trove of information regarding the overall chemical inventory and on how organics form in a region of active star formation. It harbors the promise of a deep understanding of the chemistry of space once we have the full spectral surveys available.”

Resources and quotes for this article came from http://www.herschel.caltech.edu/index.php?SiteSection=News&NewsItem=nhsc2010-003. Larger versions of the image are available at http://www.herschel.caltech.edu/index.php?SiteSection=ImageGallery&ViewImage=nhsc2010-003a.

More information on Herschel is at the Herschel website: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=16.

The HEXOS website is at http://www.submm.caltech.edu/hexos/

There is a related Space.com article at http://www.space.com/scienceastronomy/herschel-life-molecules-100311.html.

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UMRAO Contributes to Groundbreaking Research

diagram of a blazarMost large galaxies harbor a monster at their core in the form of a supermassive black hole. Most of them are like the one in our own galaxy: quiet and barely noticeable except through their gravity. However, a huge disk of dust and gas called an accretion disk surrounds a few of them and feeds the black hole. Sometimes, material from the disk gets caught in the magnetic field before it falls into the black hole, and the magnetic field sends this material flying out into space at near light speed in two jets pointed in opposite directions, roughly perpendicular to the accretion disk. If that jets happens to be aimed in our direction, the galaxy appears exceptionally bright, and we call it a blazar (see image at right.)

image of 3C 273Blazars are among the most distant objects we can see, which makes them one of the most difficult objects to understand. A new study by the Fermi-LAT Collaboration and the 3C 279 multi-band campaign published in the February 18th edition of Nature combines nearly a year’s worth of observations of a blazar named 3C 279 (radio image at left), and show us we don’t really understand them as well as we thought.

By comparing many different observations, including those made by UMRAO, the collaborators found that some of the things we though we knew about blazers are wrong. Astronomers thought the gamma rays came from the accretion disk close to the black hole, in a region no more than a few light days across. But the observations show they must originate from an area about a light year from the black hole, thousands of times farther away than previously thought. They also compared the polarization or the angle of the electric field of the light and found it rotated during the observations. Although there are a few possible explanations for this, the best explanation is that the jet has a bend, indicating the jet may change orientation over time rather than being stable as previously thought.

Studies like this show how large groups of collaborators working on different projects can bring their work together to make unexpected discoveries.

The paper appeared in the 18 February issue of Nature, available at http://www.nature.com/nature/journal/v463/n7283/full/nature08841.html along with a related article with a diagram of what this blazar might be like at http://www.nature.com/nature/journal/v463/n7283/full/463886a.html. Additional information for this article was taken from http://home.slac.stanford.edu/pressreleases/2010/20100217.htm

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Will JWST Be Able to Observe “Dark” Stars?

Super-massive black holes form the core of almost every nearby galaxy, and many astronomers believe they are necessary for galaxy formation. But where do they come from?

According to a team of astrophysicists including Monica Valluri and headed by Katherine Freese of the physics department, they might come from super-massive dark stars. In a recent paper, they say that the very first stars to form in the universe may be “dark” stars, powered primarily by dark matter annihilation. Astronomers call them dark stars because of their energy source, and may actually be quite bright.

We don’t know exactly what dark matter is, but we do know a few things about it. Most dark matter is some sort of particle that does'’t interact with normal matter very easily except through gravity. These properties led astronomers to call them “weakly interacting massive particles,” or WIMPs. WIMPs are their own anti-particle, so they annihilate each other whenever they come into contact.

Normal stars don’t collapse under their own weight because the energy generated by fusion in their core supports the star against gravity. The first stars to form in the early universe formed inside halos dominated by dark matter. As the star condenses, WIMPs are pushed together and annihilate each other, releasing enough energy to support the star against gravity.

James Webb Space TelescopeThere is enough energy released to make the dark star very puffy and large, which makes it very bright. However, since WIMP annihilation only needs high density, not high temperature, the dark star remains cool, so most of its light is in the infrared. That’s just perfect for the James Webb Space Telescope, set to launch in 2014. Because these stars are so bright at the wavelength range JWST is designed to detect, some of them may be visible as far back a z=15, when the universe was only about a quarter of a billion years old.

The dark stars remain cool for so long that they keep accumulating mass. According to their paper, “[d]ark stars continue to accrete mass as long as the dark matter annihilation powers the star and keeps it cool enough.” The mass of these stars is therefore only limited by the mass of the halo, and they could grow to be thousands of times more massive than our Sun. When the supply of dark matter finally runs out, the stars would start fusing hydrogen like “normal” stars today. After that, they quickly go supernova, leaving a super-massive black hole behind.

The paper "Supermassive Dark Stars: Detectable in JWST" by Katherine Freese, Cosmin Ilie, Douglas Spolyar, Monica Valluri, Peter Bodenheimer is listed in astro-ph as arXiv:1002.2233v1 [astro-ph.CO] and is available at http://arxiv.org/abs/1002.2233.

Information for this article was taken from the article "Did 'Dark Stars' Spawn Supermassive Black Holes?" on Discovery News at http://news.discovery.com/space/did-dark-stars-spawn-supermassive-black-holes.html.

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Two Surprising Results From A Single Object

NGC 1399A team of astronomers including Jimmy Irwin (now at the University of Alabama) and Joel Bregman has been studying an “Ultraluminous X-ray Source” or ULX in NGC 1399, an elliptical galaxy in the Fornax cluster (see image, left.) ULXs are brighter than stellar- sized X-ray sources, but not as bright as quasars. Astronomers have long suspected ULXs might be illusive intermediate mass black holes, and this team found that the most likely explanation of their observations is an intermediate mass black hole destroying a white dwarf.

Stellar mass and supermassive black holes are relatively well known. Stellar mass black holes, which may be as much as 20 times more massive than the Sun, are formed when the most massive stars die. Supermassive black holes, which have masses millions or even billions of times greater than the Sun, are found in the cores of most galaxies. However, there is a large gap between stellar mass black holes and supermassive black holes. Astronomers believe there are intermediate mass black holes of a few thousand solar masses out there, but in the original paper on this topic, they said “finding clear-cut evidence for the existence of intermediate mass black holes… has proved quite elusive.”

black hole stealing material from its companionBlack holes do not emit any light of their own, so astronomers have to look for things around the black hole.  The best way to find one is to look for one with a close companion. If the companion is close enough, the black hole can pull off its outer layers and the material will spiral around the black hole before disappearing behind the event horizon, rather like water spiraling down a drain (see image, right).  The material moves faster and faster as it spirals in, until it is moving fast enough to emit X-rays. The X-rays will make the matter farther out glow in the optical and UV region.

a globular clusterChandra observations revealed a ULX in a globular cluster in NGC 1399. Globular clusters are very dense, round clusters containing many thousands stars (see image, left). They are very good places for finding stars interacting, and should be good places to look for intermediate mass black holes. In particular, if a star gets close enough to an intermediate mass black hole, the black hole can tear the star apart, which should provide enough material for the black hole to become an ULX.

Irwin’s team used the Magellan I and II telescopes in Las Campanas to take the spectra of the ULX in NGC 1399. When they analyzed the spectra, they found two rather surprising things.

First was the speed the material was moving. By analyzing the spectrum, astronomers can determine how fast the material was moving, and from that determine the mass of the black hole.  The object is at least 1000 solar masses, making this a perfect candidate for an intermediate mass black hole.

Additionally, the material contained almost no hydrogen. Normal stars, like the Sun, are mostly hydrogen, so the material can’t be coming from a normal star.  The spectra show a large amount of oxygen and nitrogen. When stars a little more massive than the Sun die, they leave their core, made mostly of oxygen, behind as a white dwarf. So, if the object being torn apart is a white dwarf, the spectra would show a lot of oxygen.
"We think these unusual signatures can be explained by a white dwarf that strayed too close to a black hole and was torn apart by the extreme tidal forces," said Joel Bregman.

White dwarfs don’t have an atmosphere to lose like most stars, so the black hole isn't just slowly stealing the upper layers; it is ripping the entire star to shreds. This marks the first observation where astronomers can say that a black hole is completely destroying a star without being at the center of a galaxy.
"People have made cases for stars being torn apart by supermassive black holes in the centers of galaxies before, but this is the first good evidence for such an event in a globular cluster," said Jimmy Irwin.

The nitrogen in the spectrum remains unexplained however. According to Irwin, "That's something we can't yet explain with a white dwarf being torn apart, but we're thinking hard about an explanation."

Jimmy Irwin, a former post-doc at UM and now at the University of Alabama, and Prof. Joel Bregman discussed their unexpected findings at a press conference at the American Astronomical Society meeting in Washington DC on Jan 4, 2010. 

Material for this article came from the AAS press kit for the AAS Winter 2010 meeting and the Chandra press release, http://chandra.harvard.edu/press/10_releases/press_010410.html.

The original publication on these observations is “Evidence for a Stellar Disruption by an IMBH in an Extragalactic Globular Cluster” by Irwin, Brink, Bregman and Robets, submitted to the Astrophysical Journal Letters and available at http://arxiv.org/abs/0908.1115

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New Model Of Water Formation In Planet Forming Disks

Astronomers Edwin Bergin and Thomas Bethell of the University of Michigan have a new model that can explain where the water for terrestrial planets came from.

Planet forming disks in the Orion nebulaPlanets form in the disk of dust and gas that forms along with a star.  The heaviest materials like dust tend to sink to the center of the disk, leaving lighter material like water and OH in the upper levels. Astronomers had thought that the water would be destroyed by UV light from the star, which can knock a hydrogen atom off the water leaving OH or free oxygen behind.  However, observations from the Spitzer Space telescope show that the amount of water does not decrease significantly as the dust decreases.

"When you're close to a star, the radiation is destructive to most molecules. But we were able to prove that water could form quickly enough to shield itself and other molecules from that radiation," said Ted Bergin in an interview with the UM news service.

At temperatures of around 300 K (a little warmer than room temperature), oxygen quickly combines with any available hydrogen, so water molecules re-form as quickly as they are broken apart. UV light hitting the newly re-formed water will break the water apart, but again it quickly reforms. The water in the highest layers forms a protective layer that shields the water and other molecules deeper down.  

In addition, the water will protect any organic molecules in the deeper layers where planets form. In the Science article, they wrote “Some of this water and organic material could potentially be incorporated into nascent Earth-like worlds.”

"There's a rich organic chemistry that precedes the birth of stars," Bergin said. "It's simpler, but similar to the chemistry of life. The behavior of water can allow that chemistry to proceed. Without the protection water vapor provides, those organic molecules would be destroyed."

The original paper "Formation and Survival of Water Vapor in the Terrestrial Planet–Forming Region" appeared in the 18 December 2009 issue of Science.

Information and quotes for this article were taken from the UM News Service story at http://www.ns.umich.edu/htdocs/releases/story.php?id=7461.
The image comes from the Astronomical Picture of the day, Image credit: NASA, ESA, M. Robberto (STScI/ESA), the HST Orion Treasury Project Team, & L. Ricci (ESO)

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Michigan Astronomer searches for the origins of organic molecules

Artist's concept of the Hershel Space TelescopeWhen the Herschel space telescope launches later this month, it will carry with it an instrument that will be used by a professor here at Michigan.

Associate Professor Edwin Bergin is co-investigator on the Heterodyne Instrument for the Far Infrared (HIFI) carried on board the Herschel Space Telescope. Heterodyne spectrometers allow very complex analysis of light by mixing the incoming signal with a reference source, so astronomers can determine not only what wavelength the incoming light is, but also other information like the phase and amplitude. This instrument will cover 157-625 microns, which is in the far infra-red region of the electromagnetic spectrum. Water and several organic molecules emit light in this region. Also, Herschel’s instruments will be the first to study the far infra-red region of the spectrum, which opens up the possibility of discovering new molecules.

"We'll be studying the full extent of chemistry in space and we hope to learn what types of organics are out there as a function of their distance from a star," Bergin said.

Previously, astronomers have detected organic molecules in interstellar gas clouds, and have found organic molecules, including amino acids, inside of meteorites. According to Bergin, “that leads to the intriguing possibility that the chemistry ongoing in space and associated with the birth of our planet may have aided in the formation of life.”

A planet forming diskWhat astrobiologists really want to know is whether or not those molecules could have made it to a planet like Earth. With Herschel and HIFI, they will be able to look at the distribution of molecules in the disks around young stars where planets are forming. They hope this information will help answer questions about how these molecules originated on Earth. In particular, could complex organic molecules be present on a planet from the time of its formation, or do the molecules need to develop on the planet.

"The chemistry of space makes molecules that are the precursors of life. It's possible that the Earth didn't have to make these things on its own, but that they were provided from space,"

Professor Bergin is also part of a project to look for water in the planetary disks.
The current model for planet formation says Earth was too warm to have water when it formed, so the water on the surface now had to be brought to Earth via impacts from asteroids and comets. Observations with Herschel will help test if this is true.

Astronomy may not be able to answer the question of how life started on Earth, but it will help. However, answering the question of how much is out there and how it’s distributed could tell us something about life in the rest of the universe. “Maybe the stuff that made us is common throughout the universe, and hence maybe we’re not alone.”

Information and quotes for this article were taken from the UM News Service story at http://www.ns.umich.edu/htdocs/releases/story.php?id=7122 and the podcast, available from that page.
Additional information came from the Herschel website: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=16

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Local Radio Observatory Important To Understanding Distant Galaxies

Two radio astronomers from Michigan have contributed to an international study of active galactic nuclei.

Mojave-fermi image

AGNs are galaxies whose cores emit more electromagnetic radiation than the rest of the galaxy. Many of these galaxies have radio jets, formed by a central massive black hole.

M87 image from HubbleAstronomers believe most galaxies have a massive black hole at their core. Massive black holes have strong magnetic fields, and charged particles can get caught in the magnetic field. If there is a lot of material falling into a black hole, some of if will get caught and flung out of the galaxy along the pole of the magnetic field. This results in two “beams” of charged particles that stream out from the center of the galaxy. The particles emit radio waves as they travel along the magnetic field, forming the radio jets.

Most AGNs also emit gamma-rays, and there has been a long debate about whether the gamma rays and radio waves are connected. A new paper led by Yuri Kovalev and co-authored by Professor Hugh Aller and research scientist Margo Aller indicates that they are indeed connected. It was published in the Astrophysical Journal Letters on May 1.

UMRAOAstronomers at the UM Radio Astronomy Observatory (UMRAO) participate in MOJAVE, a program for long term monitoring of active galaxies. Astronomers compared MOJAVE data to data collected by the Fermi Gamma Ray Space Telescope. What they found was a strong correlation between the gamma ray and radio observations. AGNs that are stronger radio sources are also stronger gamma ray emitters. The changes in emission occur on the same timescale for both types of radiation. Additionally, the source of radiation is a very compact region in the centers of the galaxies.

AGNs were much more common in the early universe, which means most of the ones we see now are very far away. The great distance makes them difficult to observe. It can be difficult to even tell what part of a galaxy the light is coming from.

According to Hugh Aller, "the findings help us begin to understand the physical processes going on in these remote active galactic nuclei, which have been very difficult to observe. These objects are a great mystery."

Paper:
http://www.iop.org/EJ/abstract/1538-4357/696/1/L17/
News story:
http://www.ns.umich.edu/htdocs/releases/story.php?id=7107
MOJAVE:
http://www.physics.purdue.edu/MOJAVE/
Fermi Space Telescope
http://fermi.gsfc.nasa.gov/
UMRAO
http://www.astro.lsa.umich.edu/obs/radiotel/index.php

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Professor Fred Haddock dies

Emeritus Professor Fred T Haddock died Feb. 20 2009.

Professor Haddock was a pioneer in many ways. During the second World War, he helped develop a radar antenna that could be used inside a submarine periscope. After the war, he started in the field of Radio Astronomy, and was the first to discover thermal radiation from the Orion nebula, and radio bursts from solar flares. He joined the faculty at Michigan in 1956, where he designed and managed the construction of the radio telescope at Peach Mountain. Under his direction the telescope observed everything from the Sun to pulsars to quasars. He had a hand in many space exploration programs as well, including Apollo and the Voyager programs.

Professor Richard L. Sears dies

Emeritus Professor Richard Langley Sears died on Jan. 25 2009.

Dick joined the faculty of the University of Michigan in 1965. In the 40 years he spent with this department, he taught introductory astronomy to thousands of undergrads. Decades later, some of them still fondly remember his rather dry sense of humor and the unassuming manner in which he could slip the jokes into his lectures. He is the professor alumni are most likely to ask after.

In the wider astronomical community, he is best remembered for his work with Bahcall, Fowler and Iben, computing what came to be called the standard solar model, and was involved in computing neutrino emission from the sun very early in that field's development.  

Dick got his undergraduate education at Harvard, and did his PhD thesis with Marshal Wrubel at Indiana.  He held research positions at Indiana, Princeton, UC and Caltech before coming to Michigan.

He is survived by his wife Yvonne and daughter Amber.

Share your memories and read what others have to say at http://www.astro.lsa.umich.edu/donors/remember/Sears.php

 

Charles Steidel delivers 2009 Mohler Prize lecture “Witnessing the formation of galaxies: Violence in the young universe”

Charles Steidel will speak about observations of the early universe, and how that affects what we see in the universe today. Since light takes time to reach us, we see distant objects as they were long ago. The farthest objects we can see are so far away, we see them as they were 13 billion years ago. In his description of his talk, he says “… we can observe directly what the universe looked like up to about 13 billion years ago, and all times in between, up to the present. We now know that there was a particularly spectacular, and sometimes violent, period when the Universe was in its youth… where the process of galaxy formation was especially intense.”

Charles C. Steidel is the Lee A. DuBridge Professor of Astronomy at the California Institute of Technology. He received an A.B. from Princeton University and a Ph.D. in Astronomy from the California Institute of Technology. He has been a hubble Fellow at UC Berkeley, and was an Assistant Professor at MIT before moving to Caltech. He specializes in galaxy formation, and uses both large ground based and space based telescopes for his observations. He has received numerous awards, and was elected to the National Academy of Sciences in 2006. On Jan 23, he will receive the Orren C Mohler Prize.

Orren C. Mohler was a former department chair, and was director of the McMath-Hulbert Observatory in Lake Angelus Michigan. The Mohler prize was established in 1986 after his death.  Three past Mohler prize recipients have gone on to win Nobel or Crafoord Prizes.

The 2009 Mohler Prize lecture is scheduled for Friday, January 23 at 7:30 PM in 1800 Chem. This is the first in the Distinguished Lecture Series, part of the Astronomy Theme Semester. Directions and links to maps are at http://uuis.umich.edu/cic/buildingproject/index.cfm?BuildingID=34.  An open house at the Angell Hall Observatory follows the lecture.

More information and resources:

Galactic Russian Dolls Stop Star formation

M84 in X-ray (blue) radio (red) and visible (yellow and white)Astronomers have long puzzled over why some elliptical galaxies stop forming many new stars, despite having the materials to do so.  Now, an observation using NASA’s Chandra X-ray Observatory by a team of astronomers including assistant professor Mateusz Ruszkowski has an answer.

X-ray observations of galaxies show that many galaxies are surrounded by halos of hot gas. “For decades astronomers were puzzled by the presence of the warm gas around these objects. The gas was expected to cool down and form a lot of stars” said Prof. Ruszkowski in an interview with the UofM News Service.

M 84 x-ray image with circles indicating the location of bubblesThe X-ray observation of M84, a giant elliptical galaxy in the Virgo cluster around 55 million light years away, show how the supermassive black hole at the center of the galaxy may be heating the gas. The image shows that the black hole has regular, repeated outbursts, which heats the gas in the halo. “Now, we see clear and direct evidence that the heating mechanism of black holes is persistent, producing enough heat to significantly suppress star formation. These plasma bubbles are caused by bursts of energy that happen one after another rather than occasionally, and the direct evidence for such periodic behavior is difficult to find.”

The image to the right is an x-ray image of M84, with red lines showing the location of the bubbles. Some of the bubbles are inside others, like a Russian matryoshka doll. In the X-ray image, the topmost bubble appears to be in the process of popping, releasing new superheated gas into the halo and the space between galaxies.

Simulation of bubbles blown by a supermassive black holeThe team also produced a numerical simulation of the waves produced as the bubbles expand.  The simulation shows that multiple outbursts can lead to the nested bubbles in the observation. Click the image at right to see the animation of the simulation.

The repeated outbursts pump energy into the gas and dust on the galaxy and between it and other galaxies. This prevents the gas from cooling enough to form new stars. The lead author of the paper in the astrophysical journal, Alexis Finoguenov, of UMBC and the Max-Planck Institute for Extraterrestrial Physics in Germany, compares the actions of the black hole to a human heart. “Just like our hearts periodically pump our circulatory systems to keep us alive, black holes give galaxies a vital warm component. They are a careful creation of nature, allowing a galaxy to maintain a fragile equilibrium.”

The paper “In-Depth Chandra Study of the AGN Feedback in Virgo Elliptical Galaxy M84” appears in The Astrophysical Journal, 686:911–917, 2008 October 20.
additional material for this articles comes from http://www.ns.umich.edu/htdocs/releases/story.php?id=6837 and
http://chandra.harvard.edu/photo/2008/m84/

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Two Michigan Astronomers Selected to Help Guide New X-ray Observatory

Michigan Astronomy professors Joel Bregman and Jon Miller have been selected to serve on the Science Definition Team for the International X-ray Observatory (Formerly Constellation-X).

IXO will is a joint venture between the United States (NASA), Europe (ESA), and Japan (JAXA). It will study some of the most compelling ideas and problems in the universe, including the evolution of large-scale structure, the nature of space and time close to black holes, ultra-dense states of matter, feedback cycles, and the first quasars. Michigan is the only US institution to have two scientists on the team.

Visit the IXO website at http://ixo.gsfc.nasa.gov/

Installation of Dennison Mural Begins

line drawing of radio telescope on Dennison windowInstallation of the astronomy Chemed window mural began on September 26 with a line drawing of a radio telescope on the eastern-most windows (Click the images for a bigger version).

Jim Cogswell working on the muralOver the next several weeks, Prof. Jim Cogswell will add several more images, ranging from equations to a gamma-ray image of the Milky Way.  The images were provided by faculty in the astronomy department, based on their current projects and research.

The window mural is the first of many projects planned for the Winter ’09 Theme Semester and International Year of Astronomy. 

the gamma ray Milky Way

Astronomers Rediscover Young Supernova Remnant

One type of supernova occurs when a massive star dies: its outer layers collapse then bounce off the core causing a massive explosion. Normally, a supernova should occur roughly every 50 years in our galaxy.  The last time a supernova was observed in our galaxy was Kepler’s supernova in 1604, and there are only a few dozen supernova remnants (SNRs) known to have occurred during all of human history. Astronomers have long believed the “missing” supernovas occurred in dusty regions that block the visible light.

When massive stars collapse, the outer layers expand away, forming the SNR. A typical SNR expands away from the center point in roughly spherical shells, so they have a roughly spherical shape. The core of the star is usually left behind, as a central compact object (CCR).

Radio and X-ray composit image of SNR350.0-0.3When astronomers first pointed their radio telescopes at G350.1-0.3 in the early 70s, the light coming from it indicated it might be a SNR. But radio observations in the mid-80s showed an irregular shape that didn't really look like a SNR (the white lines in the image at left).  Many astronomers thought it was more likely a background galaxy, so it was downgraded to a SNR candidate and was even taken off many lists of SNRs. G350.1-0.3 was mostly forgotten.

Then in 2005, new data were published, which indicated that G350.1-0.3 had to be between 15 and 34.9 thousand light years away.   Astronomically speaking, that’s practically on our back doorstep, and definitely in our own galaxy.  There was no way this could be a background galaxy. 

A team of astronomers, which included Jon Miller of UofM, led by Bryan Gaensler and Anant Tanna of the University of Sydney used the European Space Agency’s XMM-Newton X-ray observatory to look at G350.1-0.3, and reviewed some earlier radio observations.  Their observations lead them to conclude that G350.1-0.3 is in fact a SNR.

The light coming from G350.1-0.3 indicates that it is exactly the kind of material you expect from a supernova caused by the collapse of a massive star.  They found it is a mere 15 thousand light years away and is roughly 900 years old. The strange shape comes from the surrounding material. G350.1-0.3 is in a dense, dusty area of the galaxy, so the material did not expand evenly.  It is so dusty in fact, that according to Gaensler “Even if you'd been looking straight at it when it exploded, it would've been invisible to the naked eye.”

G350.1-0.3 in x-rayAdditionally, there is an object very close to G350.1-0.3, the round blue object on the right side of the image, called XMMU J172054.5-372652 that appears to be a neutron star, a common type of CCR. It may seem odd that the CCO is not actually at the center of G350.1-0.3, but there are two possible explanations for this.  In other supernovas, the CCO has been “kicked out” of the central region by the explosion, so that after a few thousand years it is no longer anywhere near the center. XMMU J172054.5-372652 is rather far from G350.1-0.3 for this to be the case, but it isn't impossible.  The other possible explanation is that XMMU J172054.5-372652 is actually at the center of the SNR, and the region is so dusty that another component of the SNR is actually still hidden from our view.

G350.1-0.3 is the most recent of several young SNRs discovered in recent years in our galaxy.  So far, all the newly discovered young SNRs have been in dusty regions, and were only discovered after observations with x-ray and gamma ray telescopes.

This research was published as “The (Re-)Discovery of G350.1−0.3: A Young, Luminous Supernova Remnant and Its Neutron Star”, B. M. Gaensler, A. Tanna, P. O. Slane, C. L. Brogan, J. D. Gelfand, N. M. McClure-Griffiths, F. Camilo, C.-Y. Ng, and J. M. Miller; The Astrophysical Journal Letters, 680:L37–L40, 2008 June 10
Additional information and quotes for this article were taken from the ESA news article “Detective astronomers unearth hidden celestial gem” at http://www.esa.int/esaCP/SEM1OPUG3HF_index_0.html
The radio and x-ray composite image came from http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=42879

Related stories:
Neutron star observations provide groundbreaking test of relativity.
 

Imaging Stars with CHARA

main dome and some of the small telescopes at Mt WilsonThe Center for High Angular Resolution Astronomy (CHARA) is a six telescope optical/infrared array on Mount Wilson in California. Astronomers the University of Michigan designed and built the infrared combiner used to image the surfaces of stars and close binaries. John Monnier gave an invited talk at the summer 2008 meeting of the American Astronomical Society (AAS) on “Imaging with the CHARA Interferometer.”

Hubble deep fieldProfessor Monnier began his talk with the Hubble Deep Field image, to illustrate how difficult it is to study stars.  In this image, galaxies billions of light years distant are resolved well enough to distinguish their types and basic characteristics.  However, the one star in the image, identifiable by the diffraction spikes, is a single point of light. That star is within our own galaxy, a few thousand light years distant at most.  In order to resolve even the closest stars, we need 10 times better resolution than the resolution we need to identify most distant galaxies in the universe.

The CHARA interferometer has a resolution of 0.3 – 1 milli-arc-second. That’s roughly the same as being able to distinguish a human hair at a distance of 10 football fields, and is small enough to resolve large surface features on nearby large stars. The first star imaged by CHARA was Altair, and the results were published in Science in May 2007.

According to the Von Zeipel model, massive stars that rotate rapidly should exhibit gravity darkening.  The equatorial region of a rapidly rotating star will bulge out, allowing it to cool, which causes it to become somewhat dimmer. This effect is known as gravity darkening. Since the equator is dimmer than the pole, the angle of the star with respect to us can affect how bright the star looks.  For example if we are looking at the star’s pole, it will look brighter than it should, which will cause astronomers to underestimate its distance from us, and overestimate its mass.

ALtair and modelCHARA images of Altair show it is longer on one axis than the other and exhibits equatorial darkening, clearly indicating it is a rapid rotator. However, the amount of darkening seen in the observations is greater than that predicted by the Von Zeipel model. This is probably because the model assumes the stars rotate like a solid body, like the Earth.  The observations fit better with models that assume differential rotation, like the Sun, where the equator actually rotates faster than the poles. 
CHARA has also imaged Vega, Achenar, Regulus, and Aldeberan, and shown all of them are rapid rotators that exhibit gravity darkening.  Papers on these stars are forthcoming.

These models could eventually be used to measure the mass of individual stars.  The temperature gradation shows the star’s inclination and shape.  The shape can be used to determine the centrifugal force, which is determined by gravity.  Since gravity depends only on the mass, knowing the force of gravity leads to the star’s mass. Observations to test this are being planned.

In addition to imaging individual stars, CHARA holds great promise for imaging tight binary systems. A team headed by graduate student Ming Zhao recently imaged beta-Lyrae, the tightest binary system ever resolved. Their image partially resolves the accretion disk between the two stars. CHARA can resolve features as small as 150 micro-arc-seconds for close binary stars.

More information and images will be coming out soon, in the paper “First Resolved Images of the Eclipsing and interacting binary \beta Lyrae” by M. Zhao, D. Gies, J. D. Monnier, N. Thureau, E. Pedretti, F. Baron, A. Merand, T. ten Brummelaar, H. McAlister, S. T. Ridgway, N. Turner, J. Sturmann, and L. Sturmann, which is currently undergoing review.

Related stories:
Astronomers Capture First Image of the Surface of a Sun-Like Star

Student Image Included In Podcast

L1157 in Infra-redThe image of a young star system taken by a team of astronomers that included graduate student John Tobin was recently included in a Spitzer Space telescope HD video podcast on protostellar jets. The podcast tells about what we can learn from infra-red images of very young star systems. The image was used as an example of a jet that can only be seen by observing in the infra red. 

Download and view the podcast at http://www.spitzer.caltech.edu/features/hd/files/HUHD_019_ProtostellarJets.m4v.  You can view other Hidden Universe High Definition vodcasts or subscribe to he series by going to http://www.spitzer.caltech.edu/features/hd/index.shtml.

The original image press release and full credits are available at http://www.spitzer.caltech.edu/Media/releases/ssc2007-19/ssc2007-19b.shtml
Also, check out the original article about this under Related Stories below.

Related stories:
A Protostellar Envelope in a Young Stellar System
 

UM astronomers help reveal origin of black hole jet

Blazars are some of the most energetic objects in the universe.  They are a type of active galaxy similar to a quasar, powered by massive black holes at their core, and fueled by the stars and gas near the center of the galaxy.  The exact mechanism for their exceptionally bright jets was uncertain until recently.

artist's rendition of a blazarWhen the stars and gas get too close to a black hole, they get caught in its gravity.  The gravity of the black hole is so great it rips the material apart, eventually turning it into plasma.  The material has too much inertia to fall straight into the black hole.  Instead it orbits several times before falling in, forming something astronomers call an accretion disk. The orbiting plasma generates a magnetic field, which is twisted into a corkscrew pattern by the rotation of the accretion disk and black hole. Some of the charged particles get caught in the magnetic field before they get too close to the black hole and are flung out at near light speed along the twisted magnetic field.  The image at left shows an artist's concept of a black hole with an accretion disk and jets.

The theoretical models for blazars predict that the supermassive black hole at the center of the galaxy should have an incredibly strong magnetic field and a huge accretion disk. The particles should emit light as they travel along the magnetic field, appearing as a jet from the center of the galaxy. Astronomers should be able to observe the change in polarization of the light from the jets – the same property of light that allows polarizing sunglasses to cut down on glare from horizontal surfaces.  Additionally, the particles should brighten drastically when they hit a shock wave, creating a temporary brightening in one location along the jet. An animation is available at http://www.bu.edu/blazars/bllac_files/agn_nature_cam3_360sqpix.mov

An international team of astronomers headed by Alan Marscher of Boston University observed BL Lacertae, a blazar about 950 million light years from Earth.  The team included University of Michigan radio astronomers Margo and Hugh Aller, as well as visible, x-ray and gamma ray observers.  The results are amazing.

"This is the first observational evidence that really fits with the picture that the theoreticians have had," said Margo Aller, a University of Michigan radio astronomer. According to Alan Marscher "We have gotten the clearest look yet at the innermost portion of the jet, where the particles actually are accelerated"

Other observations have been unclear about what was happening. "What's really been a mystery was that we could see there were these really high-energy particles, but we didn't know how they were created, how they were accelerated. It turns out that the model matches the data. We can actually see the particles gaining velocity as they are accelerated along this magnetic field,” said Hugh Aller. 
According to Margo Aller, "The reason we have this evidence is a very fine sampling of a large number of instruments, including the Michigan radio telescope." 

The Michigan Radio Telescope is located at the Peach Mountain Observatory in Dexter.  It has been in operation since 1958.  It is open to the public on the third Sunday of September every year, from 2 - 4:30 in the afternoon.

More on this topic is available from
http://www.ns.umich.edu/htdocs/releases/story.php?id=6499
http://www.reuters.com/article/scienceNews/idUSN2338757920080424
http://www.space.com/scienceastronomy/080428-mm-black-hole-blazar.html
Images and animations are from
http://www.bu.edu/blazars/BLLac.html
The letter "The inner jet of an active galactic nucleus as revealed by a radio-to-big gamma-ray outburst" appeared in the 24 April 2008 Nature, vol 452 pp 966-9 available at
http://www.nature.com/nature/journal/v452/n7190/full/nature06895.html

Related stories:
New Movies Help Astronomers Understand Active Galactic Nuclei
Triple Quasar Systems Common in the Early Universe
Black Holes Light Up the Universe

 

New Movies Help Astronomers Understand Active Galactic Nuclei

M87 in radioUniversity of Michigan radio astronomers Hugh and Mago Aller are members of the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) program. MOJAVE recently released movies of 100 jets from active galactic nuclei.

Centaurs A composit: optical, radio, 21 cm and x-rayActive galaxies have unusually bright centers (galactic nuclei).  Quasars are the most well known and brightest type of active galaxy.  Active galactic nuclei are typically much brighter than average at shorter wavelengths, and usually have a radio lobe directed perpendicular to the plane of the galaxy.  (The image at right is a multi-wavelength composite of the Centaurs A galaxy.  The dusty disk runs lower left to upper right, and the green colored radio jet runs upper left to lower right.  Click the image to go to the Chandra page to see the individual images that went into the composite.)

Active galactic nuclei are driven by a black hole with an accretion disk.  Material will orbit a black hole several times before falling in. The orbiting material tends to form into a disk around the black hole, called an accretion disk.  Before falling in, some of the material can be accelerated enough to get kicked up out of the accretion disk.  This material emits radio waves, and forms the radio jets.  Understanding these jets helps astronomers understand the black holes and accretion disks that power the active galactic nuclei.

There have been some surprises in the observations. For example, some components of the jets appear to be moving faster than the speed of light.  Other jets appear to twist around erratically, change direction, or show sudden changes in their magnetic field. A few galaxies even appear to have only one radio lobe instead of two. Detailed observations are needed to understand what is really happening in all these cases.

The MOJAVE project regularly images jets from active galaxies.  It began in 2002, and is a successor to an earlier VLBA (Very Long Baseline Array) that ran from 1994 to 2002.  In January ’08 it released data from over 100 objects as time-lapse movies.

In particular, astronomers hope to combine these data with observations from NASA’s GLAST satellite, which is expected to launch in May ’08.

More on the MOJAVE program, and the movies, are available at http://www.physics.purdue.edu/MOJAVE/
The press release about the movies is at http://www.nrao.edu/pr/2008/mojave

U of M astronomers detect young solar systems

Graduate student Catherine Espaillat and professor Nuria Calvet are part of a group to detect what may be the youngest solar systems ever detected.

The group used the Spitzer Space Telescope’s infra-red cameras to study two systems, UX Tauri A and LkCa 15. Both are very young systems, and the stars are still surrounded by a protoplanetary disk. “They’re baby stars” according to Calvet.

Artists representation of system UX Tau APrevious observations of other young star systems have turned up disks with large empty regions in them. There are two leading hypotheses about how these gaps form. One idea is that protoplanets in the disk sweep up material, clearing a path. Another idea is that photoevaporation clears the disk.

In photoevaporation, light from the star hits the material in the disk causing it to evaporate and dissipate into space. In this model, the disk would slowly clear from the center out. The hole would gradually increase in size until the system is cleared of dust and gas. Astronomers would expect to observe a solid disk with a big hole in the center.

If instead, protoplanets sweep up the material in the disk, astronomers would expect to see material close to the star, then almost nothing in the region where the planets are forming, then the disk would pick up again. Astronomers would expect to see a disk with gap in it.

Using detailed measurements of the light coming from these two systems, astronomers determined the disks around these systems have the beginnings of a gap. “It's more like a lane has been cleared within the disk. That is not consistent with photoevaporation. The existence of planets is the most probable theory that can explain this structure." Said Espaillat.

This helps astronomers understand more about the formation of stars and solar systems, including our own. "We are looking for our history," Calvet said. "We are looking for the history of solar systems, trying to understand how they form."

The study “On the Diversity of the Tarus Transitiona Disks: UX Tauri A and LkCa 15” appeared in the December 1 Astrophysical Journal Letters.
Associated Stories appear at
http://www.spitzer.caltech.edu/Media/happenings/20071128/
http://www.ns.umich.edu/htdocs/releases/story.php?id=6205

The research has also garnered a lot of press in Spanish language media. You can read more at any of these Spanish language sites:
La investigación también ha recibido muchos de atención en la media español. Lea más en estos sitios españoles:
http://www.ns.umich.edu/Es/_story.php?id=6206
http://actualidad.terra.es/ciencia/articulo/astronomas_via_lactea_2072564.htm
http://www.farodevigo.es/secciones/noticia.jsp?pRef=3188_26_182600__Ciencia-y-Tecnologia-astronomas-Michigan-encuentran-sistemas-solares-bebe-Lactea
http://www.diariocordoba.com/noticias/noticia.asp?pkid=366580
http://www.lavozdeasturias.es/noticias/noticia.asp?pkid=381598
http://www.esmas.com/noticierostelevisa/internacionales/681837.html
http://www.tiempo.com.mx/not_detalle.php?id_n=39178
http://www.elimparcial.com/EdicionEnLinea/Notas/Cienciaytecnologia/28112007/275551.aspx
http://www.lostiempos.com/noticias/28-11-07/28_11_07_ultimas_vyf5.php

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A Protostellar Envelope in a Young Stellar System
Water vapor observed in young star system
Solution to Cometary Puzzle Found in Interstellar Clouds

A Protostellar Envelope in a Young Stellar System

L1157 in Infra-redGraduate student John Tobin is part of a team that recently used the Spitzer Space Telescope to capture an infra-red image of dark cloud L1157 in the constellation Cepheus, and shed new light on star formation.

Most star formation models begin with a roughly spherical envelope of gas and dust that eventually collapses into a flat disk with a new star at the center. Many flat, protoplanetary disks have been observed around young stars, but this is the first observation of a flattened envelope. Models also predict that as the envelope collapses, material from the envelope falls onto the protostar. Some of that material is blown out into space in jets that flow perpendicular to the envelope. By this model, protostars with jets should have flattened envelopes laying perpendicular to the jets.

The dark cloud L1157In visible light, L1157 appears as a dark cloud because the dust in the area absorbs the visible light. At other wavelengths, L1157 is much more interesting. The jets glow brightly at radio wavelengths and in the infra-red. In areas where the dust is thin, infra-red light is emitted. However, where the dust is very thick, even the infra-red light is blocked.

Spitzer’s infra-red image of L1157 show the bright jets previously observed in radio, and a dark feature perpendicular to those jets. The jets are so long that light would take nine months to travel from the star to the ends of the jets. The dark feature looks like a thick disk oriented perpendicular to the jets. It is large: more than a thousand times bigger than our entire solar system. Its appearance matches well with current theories of star formation. Asrtonomers estimate the protostar at the center should begin fusion and become a star similar to our Sun in about a million years.

The study, titled “A Flattened Protostellar Envelope in Absorption Around L1157”, was published in the December 1 edition of the Astrophysical Journal Letters. The study authors are Leslie Looney, John Tobin and Woojin Kwon.

Material for this article was taken from the ApJl, and from a Sptzer press release, available at http://www.spitzer.caltech.edu/Media/releases/ssc2007-19/release.shtml

Related stories:
Water vapor observed in young star system
Solution to Cometary Puzzle Found in Interstellar Clouds

Featured Image includes data from UM astronomer

M74 Spiral GalaxyThe Hubble Heritage site recently featured an image of M74 that includes data taken by Prof. Jon Miller. The image was chosen for its "[resemblance to] festive lights on a holiday wreath" by the Hubble Heritage team.

Dust in the disk of the spiral galaxy scatters blue light more than the other colors, giving the dusty arms their blue color. Hot young stars ionize the hydrogen gas around them. The gas glows a pinkish red, like holiday lights on a wreath.

Other versions of the image are available on the Hubble Heritage sight, at http://hubblesite.org/newscenter/archive/releases/2007/41/

 

Comet Holmes Joins the Autumn Skies

The Autumn skies hold many favorites for amateur and professionals alike. The only galaxy visible to the naked eye in the northern hemisphere (not counting the one we're in) resides in the constellation Andromeda. A jewel for small telescopes, the Perseus double cluster sits nearby. Perseus also holds the disappearing "demon star" Algol, next scheduled to vanish in the evening on November 7.

Comet Holmes and part of PerseusThis year, comet 17P/Holmes joins the group, and it's the first naked eye comet we've had in the northern hemisphere in a couple years. Graduate student John Tobin snapped a couple pictures of comet Holmes on Oct 26 using a standard digital camera piggybacked on a small telescope while working at the MMT. Before Oct 24, Holmes was a dim 17th magnitude object, undetectable without at least a very good backyard telescope. But on the 24th, Holmes suddenly brightened to 2nd magnitude, making it about as bright as the stars in the Big Dipper. And it's not the first time that's happened. Holmes was originally discovered in 1892, when it also suddenly brightened.

Although astronomers aren't sure why this happens, they do have a working hypothesis. Comets have a nucleus made of a mix of ices and rock. When the nucleus gets close to the Sun, the ice sublimates, creating a gaseous shell, or coma around the nucleus, and two tails: the ion tail that points away from the Sun and the dust tail that lays back along the path of the comet. The more gas there is, the bigger and brighter the coma and ion tail are. Some comets show signs of being porous, like swiss cheese. Those holes sometimes collapse, suddenly exposing a lot more ice to the Sun. The coma can suddenly become a lot bigger. To actually test this hypotheses, space scientists need to send out more probes, like Deep Impact.

Although visible to the naked eye, comet Holmes is best viewed with a good pair of binoculars. You don't need anything powerful, 7x50 will do quite nicely, but you do want something that gives you a clear image without distortion. To find comet Holmes, you'll need clear skies to the northeast. Head outside after about 8 PM through the first week in November and find the "W" shape of Cassiopeia. Drop straight down from Cassiopeia toward the NE horizon to a star that doesn't twinkle. If you look that way with binoculars, you should see a fuzzy blob.

Additional reading:

University of Michigan faculty publish three chapters in "Annual Reviews of Astronomy and Astrophysics" (Vol 45, 2007)

Annual Reviews publish articles on the current state of research in many fields.  These are some of the most highly cited articles in their fields.  The 2007 Astronomy and Astrophysics version, published in September, included 3 articles from University of Michigan Department of astronomy faculty:

"Cold Dark Clouds" Edwin Bergin
"The Warm-Hot InterGalactic Medium" Joel Bregman
"Relativistic X-ray Lines form the Inner Accretion Disks Around Black Holes" Jon Miller

Additionally, the article "A New View of the Coupling of the Sun and the Heliosphere" by Thomas Zurbuchen of the Department of Atmospheric, Oceanic, and Space Sciences at the University of Michigan also appeared, giving the university more than 1/4 of the articles in the Annual Reviews.

 

Water vapor observed in young star system

Diagram of IRAS 4B system NGC 1333-IRAS 4B, a protostellar system

A team of astronomers including Nuria Calvet and Lee Hartmann observed 30 young stellar systems using the Spitzer Space Telescope.  One of the objects, NGC 1333-IRAS 4B, showed a significant amount of water in its spectrum.

Water is a common molecule, found throughout the universe.  It has been observed throughout our solar system, in giant molecular clouds in deep space, in the atmospheres of planets orbiting other stars, and even in some cool giant stars.  It is a necessary ingredient for life.  It also thought to be necessary for planet formation: the cooling effect from water vaporization allows the gas in a protoplanetary disk to condense into the seeds that eventually form into planets.  However, until now, water has never been detected in a protoplanetary disk.

The NGC 1333-IRAS 4 system is a multiple protostar system at a distance of about 320 pc (1040 light-years). Previous observations indicated this protostellar system might have water, making it a candidate for the more recent observations.  The more recent observations show one of the protostars in the system, NGC 1333-IRAS 4B actually has a lot of water in a disk around the protostar.

Spectrum of IRAS 4B and a model water spectrumWhen star systems form, they being as roughly spherical clouds of gas and dust.  The cloud begins to rotate and collapses into a disk. For systems with a single star, such as our solar system or NGC 1333-IRAS 4B, a protostar forms near the center of the disk, and materials in the disk clump together, eventually developing into planets.  What astronomers are seeing in NGC 1333-IRAS 4B is the early formation of the disk inside the spherical envelope.  Water ice is falling out of the envelope and onto the disk, where it vaporizes. The water vapor will refreeze farther out, eventually forming into comets. In our own solar system, comets must have delivered most of Earth’s water after the planet finished forming. This is the first observation showing a water-rich disk near the protostar, and is an important step in understanding the formation of planets.

The spectrum tells astronomers a lot about the disk.  The lines indicate the temperature is about 170 K or minus 150 degrees Fahrenheit.  There is about 7.5x1024 g of water in the disk, about 5 times more water than in all the ocean of Earth. The total mass of the disk is about 6x1026 g, roughly the same mass as Earth. 

NGC 1333-IRAS 4B was the only object in the set of 30 to show significant amounts of water.  This could be due to the orientation of the system.  The light needs a clear path to escape from the disk and make it to the telescope to be detected, and NGC 1333-IRAS 4B appears to be nearly face on, so there is nothing in the way of the light.  The other possible explanation is that this process is very short-lived and happens very early in disk formation.  That would make NGC 1333-IRAS 4B a very young system.

Information for this article was taken from
http://www.nasa.gov/mission_pages/spitzer/news/spitzer-20070829.html
and the letter, published in Nature 448, 1026-1028 (30 August 2007)
http://www.nature.com/nature/journal/v448/n7157/full/nature06087.html

Neutron star observations provide groundbreaking test of relativity.

neutron star in binary systemA team of astronomers led by research fellow Edward Cackett and professor Jon Miller of the University of Michigan made observations of neutron stars.  Their observations show that the distortion of space-time predicted by Einstein’s general theory of relativity occurs around these dense objects, and provides newer and more precise techniques of measuring the properties of neutron stars.

A neutron star is the dense core left behind by the death of a massive star. A single cup of the material in a neutron star would outweigh Mt. Everest.  Adding just a little bit more mass to a neutron star could actually cause it to collapse into a black hole.

Neutron stars are the densest observable matter in the universe.  They are denser than anything scientists can create in the lab on Earth, and that makes them the best natural laboratory to study physics at extreme pressures.  Exotic particles and unusual states of matter that don’t exist anywhere else in the universe may be found in neutron stars.

Some neutron stars occur in binary systems.  Matter from the companion star may leak onto the neutron star in these systems.  However, the matter doesn’t fall straight onto the neutron star.  Instead, it may make several orbits before finally falling onto the star, forming into an accretion disk.  The gas in the accretion disk is hot, so it emits light, and the different elements in the disk emit different colors of light.

neutron star with accretion diskIron atoms in the accretion disk emit light in the x-ray region.  In a stationary lab on Earth, the light emitted by the superheated iron would form a single narrow spectral line. Cackett and Miller measured the iron line using the JAXA/NASA x-ray satellite Suzaku.  They found the line was much broader than it would be in the stationary lab.  This line broadening is caused by the Doppler effect, and provides a way to measure how fast the disk is rotating.  They also found the center of line was shifted to a longer wavelength, which is what Einstein’s theory of general relativity predicts for an accretion disk close to a dense source.  Finally, they found that the line is brighter at shorter wavelengths, which is predicted by Einstein’s theory of special relativity for anything being beamed toward the Earth.

The resolution of these measurements exceeds past measurements, allowing the first direct measurements of the inner edge of the accretion disk.  Matter in the accretion disk is moving at about 40% of the speed of light, or about a quarter of a million miles per hour.

"We’re seeing the gas whipping around just outside the neutron star’s surface," says Cackett. "And since the inner part of the disk obviously can’t orbit any closer than the neutron star’s surface, these measurements give us a maximum size of the neutron star’s diameter. The neutron stars can be no larger than 18 to 20.5 miles across, results that agree with other types of measurements."

"Now that we’ve seen this relativistic iron line around three neutron stars, we have established a new technique," adds Miller. "It’s very difficult to measure the mass and diameter of a neutron star, so we need several techniques to work together to achieve that goal."

Knowing a neutron star’s size and mass allows physicists to describe the "stiffness," or "equation of state," of matter packed inside these incredibly dense objects. Besides using these iron lines to test Einstein’s general theory of relativity, astronomers can probe conditions in the inner part of a neutron star’s accretion disk.

Cackett and Miller observed three neutron stars, Serpens X-1, GX 349+2, and 4U 1820-30. Serpens X-1 was observed earlier by Sudip Bhattacharyya and Tod Strohmayer at NASA’s Goddard Space Flight Center using the European Space Agency’s XMM-Newton x-ray satellite.  The Suzaku observations are nearly identical to the XMM-Newton observation.

Material for this article was taken from

Related papers:

 

New Observations Tell About the Origins of Stars in Our Neighborhood

View of Milky Way from the ClayStellar streams are collections of stars that move with the same speed and in the same general direction.  Recently, a group of astronomers including Thomas Bensby and Sally Oey of the University of Michigan took a closer look at one of these, the Hercules Stream.

60 stars in the local neighborhood that are part of the Hercules Stream were selected for observation last year using the Magellan Inamori Kyocera Echelle (MIKE) spectrograph (built by UM Professor Rebecca Bernstein) on the Magellan Clay 6.5-m telescope at Los Campanas Observatory in Chile.  The spectrograph allows astronomers to determine what chemical elements are present in the stars, and to estimate their ages. (Image at right is the view of the Milky Way from the Clay, Copyright R. Simcoe of MIT.)

One of the hypotheses for the origin of these streams is that they were once dwarf galaxies cannibalized by the Milky Way.  According to Oey, "[t]here is no reason to believe that the star formation history in a different galaxy with completely different conditions should be similar to the star formation history in our galaxy".  However, the observations of element abundances in the Hercules Stream stars “…show the same pattern known to exist in [our] galaxy.”  This strongly suggests the stars in the Hercules stream were not part of any dwarf galaxy, but rather formed here, in the Milky Way.

Another hypothesis for the origin of these streams is that they were large star clusters on the outskirts of the galaxy, which are now being torn apart.  However, the composition and ages of the stars appears to more closely match that of the inner part of our galaxy.  More observations are needed to confirm this. 

ngc 1672, a barred spiral galaxyThese observations strongly support the hypothesis that these streams actually result from disturbance by the bar at the center of our galaxy. Several spiral galaxies such as ngc 1672 pictured at left, appear to have a bar across the center of the galaxy.  As the bar rotates, it creates a ripple that pushes stars outward, forming a stream.  In the case of the Hercules stream, they were pushed out toward the Sun.

Further study of the Hercules stream will shed light on the dynamics of the inner galaxy, and could be a probe to measure the distribution of dark matter in the galaxy. 

This work was presented by Professor Oey in the summer meeting of the American Astronomical Society on June 6.  S. Feltzing of Lund Observatory and B. Gustafsson of the Department of Astronomy and Space Physics at the University of Uppsala also contributed to this research.  Additional information can be found at http://space.newscientist.com/article/dn11956-core-of-the-galaxy-catapults-stars-our-way.html and http://www.ns.umich.edu/htdocs/releases/story.php?id=5870.  The original paper published in the Astrophysical Journal Letters titled “Disentangling the Hercules Stream” can be downloaded from http://arxiv.org/abs/astro-ph/0612658.

Astronomers Capture First Image of the Surface of a Sun-Like Star

Normally when stars are viewed through a telescope, they appear only as pinpoints of light.  However, recent advances in optical interferometry have allowed astronomers to resolve stars as a disk and now, to actually resolve features on the surface of the star.

Altair is a relatively nearby star bright blue star in the constellation Aquila and rotates very rapidly.  In 1924, Hugo von Zeipel predicted that rapidly rotating stars would be wider across the equator than across the poles.  He also predicted that these stars would appear darker along the equator because it is farther from the star's core and therefore cooler than the poles.  This effect was dubbed “gravity darkening”.

Comparasin of CHARA Altair observation with terrestrial observationThe first resolved images of Altair were taken in 2001 and showed the star was indeed longer in one dimension than the other.  That made it an excellent target for the recently commissioned Michigan Infrared Combiner (MIRC), an instrument installed on Georgia State University’s Center for High Angular Resolution Astronomy (CHARA) interferometer on Mount Wilson on California. 

The CHARA array consists of four telescopes separated by nearly 300 yards.  Light from each telescope is sent through vacuum tubes to the MIRC, which is able to take the infrared light from all four telescopes and combine it onto one image.  The resulting images is as sharp as if it were taken by a telescope almost 300 yards wide, roughly 100 times sharper than the Hubble Space Telescope.  It is equivalent to viewing a single letter from a newspaper at a distance of 100 miles (see image at right)

Altair - model prediction and actual observationThe results of this observation show that Altair also shows the gravity darkening predicted by von Zeipel.  However, the darkening does not match the predicted values.  The image at left shows the appearance of the star as predicted by model on the left. On the right is the result of the observations.  The image shows that the area around the equator is about 60 to 70% of the brightness at the pole, which is actually darker than expected based on the theory.  In addition, the image shows some asymmetry (the change from bright to dark is not perfectly smooth).  However, these features are at the limit of the resolution for CHARA, so they may be artifacts of the instrument, not actual features.

The basic von Zeipel theory relies on some simplifications, like solid body rotation and no convection.  However, it may be that the equator rotates faster than the poles, just as the Sun does.  This observation clearly shows that while the basics of the von Zeipel theory are correct – the star is oblate and shows gravity darkening – the details of the gravity darkening laws still need to be worked out.

The next big thing for the MIRC and CHARA will include searching for earth- sized planets around other stars by looking for the minute change in the star’s brightness as the planet passes in front of, or transits, the star.

The next big thing for MIRC and CHARA will be to search for the hot glow of "hot Jupiter" planets around nearby stars.  These large planets orbit within 1/20 AU from their host star and their infrared glow should be detectable -- allowing astronomers to make an image of the planet as it orbits its star!

U-M astronomer David Berger was a co-author of the Science paper. The team also included researchers from St. Andrews University, Cambridge University, Georgia State University, California Institute of Technology, Cornell University, the Laboratoire d'Astrophysique de Grenoble in France, the Michelson Science Center, and the National Optical Astronomy Observatory. Funding for the Altair project was provided by the National Science Foundation and NASA.

Material for this article comes from the University of Michigan News Service, Science, and the National Science Foundation Press release.  Additional Materials can be found at http://www.astro.lsa.umich.edu/~monnier/Local/altair2007.html

Triple Quasar Systems Common in the Early Universe

Quasars are among the brightest and most distant objects in the universe. They form when large amounts of gas and dust fall into a supermassive black hole (SMBH), releasing enormous amounts of electro-magnetic radiation. In fact, a single quasar can outshine the entire parent galaxy.  Of the roughly 100,000 known quasars, about a hundred are binary systems.  Recently, a triple quasar system was discovered, at about 10.7 billion light years from Earth.  The light we currently receive from it left when the universe was only about 3 billion years old.

Until recently, the existence of a triple-quasar system was thought to be unlikely if not impossible.  However, a new model predicts how this system could have formed and evolved.  This theoretical work is headed by Frederic Rasio of the Weinberg College of Arts and Sciences at Northwestern, and includes Marta Volonteri of the University of Michigan, Loren Hoffman, a doctoral student at Harvard University, and Stefan Umbreit, a postdoctoral fellow at Northwestern

Galaxies in the early universe were much closer together than they are now, making mergers between galaxies commonplace.  When galaxies pass close to each other, the SMBHs at their center interact with each other, and may even go into orbit around each other.  The gas and dust in the parent galaxies may fall into the black hole, turning both SMBHs into quasars.  The SMBHs eventually merge, forming a single quasar at the center of a single galaxy.  Eventually, the gas and dust run out, leaving only the SMBH at the center, similar to our own Milky Way.

If a third galaxy with a SMBH happens by before the two black holes have had the chance to merge, a system with three SMBHs develops, possibly resulting in a triple-quasar system. The theoretical model actually predicts that interactions between three SMBHs should occur at a rate of a few per year in the early universe, making three black hole systems relatively common.

Triple systems are very unstable.  After several million years (just a few moments in astronomical terms), one of the black holes is ejected into space, leaving only a binary pair behind. Eventually, the binary pair merges into a single SMBH, just as if the third SMBH had never dropped in.

“The detection of wandering black hole binaries flying in empty space would give us a unique signature of triple interactions in the early universe” said Volonteri. “Gravitational waves emission seems to be the only way of spotting these wandering binaries.”

Detecting these gravitational waves is one of the goals of the Laser Interferometer Space Antenna (LISA) mission, currently in development by NASA and ESA.  Doug Richstone of the University of Michigan is one of the science team members for this mission.

The theoretical work was presented by Rasio at the annual meeting of the American Astronomical Society (AAS), which took place in Seattle Jan 5 – 10 2007.  Observational evidence for a three-quasar system was presented by George Djorgovski, of Caltech on the same day.  Material for this article was taken from Physorg.com http://www.physorg.com/news87493181.html, Space.com http://space.com/scienceastronomy/070108_blackhold_triple.html, New Scientist Space News http://space.newscientist.com/article/dn10915-tightknit-trio-of-%20quasars-discovered.html and Nature http://www.nature.com/news/2007/070108/full/070108-3.html (subscription required).

Comet IngredientsSolution to Cometary Puzzle Found in Interstellar Clouds

Sébastien Maret and Edwin Bergin from the University of Michigan have found evidence of atomic nitrogen in interstellar gas clouds, a finding which substantially changes our understanding of chemistry in space.

The question of why molecular nitrogen hasn't been detected in comets and meteorites has puzzled scientists for years. Because comets are born in the cold, dark, outer reaches of the solar system they are believed to be the least chemically altered during the formation of the Sun and its planets.

Studies of comets are thought to provide a "fossil" record of the conditions that existed within the gas cloud that collapsed to form the solar system a little more than 4.6 billion years ago. In this cloud, since nitrogen was thought to be in molecular form, and it follows that comets should contain molecular nitrogen as well.

But the reason it isn't there is because it isn't present in the gas clouds whose microscopic solid particles eventually form comets, said Sébastien Maret and Edwin Bergin, a professor of astronomy at the University of Michigan. Those clouds contain mostly atomic nitrogen, not molecular nitrogen, as previously thought.

This discovery also suggest that pre-life molecules may be present in comets. If nitrogen in its simplest form, the atomic form, it is much more reactive and can more easily form complex prebiotic organics in space. These complex organics were incorporated into comets and were provided to the Earth.

For more information, read the university press release at
http://www.umich.edu/news/index.html?Releases/2006/Jul06/r072606 or click the image to read about it in Astrobiology Magazine.

imageBlack Holes Light Up the Universe

A team of astronomers led by Jon Miller at the University of Michigan may know how black holes are lighting up the Universe. New data from NASA's Chandra X-ray Observatory show, for the first time, that powerful magnetic fields are the key to these brilliant and startling light shows. It is estimated that up to half of the radiated energy in the universe since the Big Bang comes from material falling towards super-massive black holes, including those powering quasars, the brightest known objects. Chandra observed a black hole system in our galaxy, known as GRO J1655-40, where a black hole was pulling material from a companion star into a disk. Miller and his team showed that the speed and density of the wind from the disk in J1655 corresponded to computer simulation predictions for winds driven by magnetic fields. The spectra from Chandra rule out the two other major competing theories to magnetically-driven winds.

The image at right is an illustration of a black hole in a binary star system similar to GRO J1655-40. The inset is a spectrum take by the U of M team. Click the image for more information, images and animations. Read the university press release at http://www.umich.edu/news/index.html?Releases/2006/Jun06/r062006