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Student Image Included In Podcast
The 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 thisunder 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.
When 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 animationa 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
University 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.
Active 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.
Previous 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
- Related stories:
- 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
Graduate 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.
In 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
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/
