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Featured Image includes data from UM astronomer

M74 Spiral Galaxy The 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.

This 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:

Images and maps (at least while the comet is still bright) will be at http://spaceweather.com/
More on observing the comet: http://www.space.com/spacewatch/071025-comet-holmes.html and
http://www.skyandtelescope.com/observing/home/10775326.html

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

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.

When 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.

A 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.

Iron 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

New Observations Tell About the Origins of Stars in Our Neighborhood

Stellar 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.

These 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 observation The 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 observation The 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).

Solution 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.

Black 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