Novel observing mode on XMM-Newton opens new perspectives on galaxy clusters

Surveying the sky, XMM-Newton has discovered two massive galaxy clusters, confirming a previous detection obtained through observations of the Sunyaev-Zel'dovich effect, the 'shadow' they cast on the Cosmic Microwave Background. The discovery, made possible thanks to a novel mosaic observing mode recently introduced on ESA's X-ray observatory, opens a new window to study the Universe's largest bound structures in a multi-wavelength approach.

Galaxy clusters are the largest gravitationally bound objects in the Universe. As such, they are extremely important probes of cosmic properties on very large scales, since they form in the densest knots of the large-scale structure, the cosmic web. Originally discovered as an excess density (or cluster) of galaxies located at the same redshift, hence the name, there is much more to these enormous structures than mere galaxies: in fact, only about one tenth of the entire mass of a galaxy cluster arises from galaxies (up to a thousand in the most massive cases), another tenth consists of hot gas, and the remainder can be attributed to dark matter.

The gas that fills galaxy clusters is hot enough to emit X-rays — with a temperature of more than 10 million Kelvin, the gas is ionised and electrons scattering off ions are decelerated, emitting radiation in the process. From measurements of the X-ray luminosity of galaxy clusters and of the gas temperature, the total mass of these structures can be estimated. This yields clear evidence that clusters are indeed gravitationally bound structures and that their mass is dominated by the elusive and invisible dark matter.

The two massive galaxy clusters discovered with XMM-Newton. Left: SPT-CL J2332-5358; Right: SPT-CL J2342-5411. (Click here and here, for extended captions and credit details.)

"Interestingly, the same hot gas we directly observe in X-rays also affects the photons of the Cosmic Microwave Background (CMB), which are passing through the cluster on their way to us," says Hans Böhringer from the Max-Planck Institute for Extraterrestrial Physics. The CMB photons interact with the extremely energetic electrons in the cluster plasma and in doing so their energy is modified in a very characteristic way, leaving a signature on the CMB — the so-called Sunyaev-Zel'dovich Effect (SZE). "We can then see clusters as 'shadows' cast on the CMB in the millimetre subset of radio wavelengths," Böhringer adds.

A survey of the sky at millimetre wavelengths, currently being carried out with the South Pole Telescope (SPT), has recently achieved its first results, detecting a dozen of previously unknown galaxy clusters by means of their SZE signature. Follow-up observations in the optical and X-rays are, however, needed in order to better characterise the physical properties of these structures and to probe how the observed SZE signal depends on the mass of the clusters.

"Using XMM-Newton, we have independently detected two of the newly discovered clusters found by the SPT," says Róbert Suhada, who led the study. Using the X-ray data, the mass of both clusters could be estimated, leading to values of over 1015 solar masses and about 3x1014 solar masses, respectively. "One of the clusters is exceptionally massive, and it ranks among the hottest clusters ever observed," adds Suhada.

The discovery was possible thanks to a new mode of observations recently implemented by the XMM-Newton Science Operations Centre. "The new mosaic observing mode enables us to survey large areas of the sky in a much more efficient way than previously," explains Maria Santos-Lleo, XMM-Newton Science Support Manager.

ESA's X-ray observatory has been operating for more than ten years, but the demand for observing time is still high and is often driven by new science goals — some of them unexpected during the project phase, over a decade ago. In some cases, the scientific objectives require the observation of sky regions larger than the field of view of the cameras aboard the spacecraft. This pushes the support scientists to implement new operating modes that optimise the performance of the instruments. "It is difficult, and very rare, to develop new modes when the spacecraft is already in orbit and operating. In this particular case, we succeeded in figuring out a novel way to exploit the instruments in order to satisfy new needs of the astronomical community," adds Santos-Lleo. Thanks to the mosaic mode, it was possible to extend the observed patch of the sky to about 14 square degrees, about 70 times the area of the full Moon.

Mosaic mode XMM-Newton image of the entire XMM-BCS survey field. (Click here for extended caption and credit details.)

Besides the SZE detection and X-ray data, optical observations of the galaxies in the two clusters enabled their redshifts to be established: z=0.3 (in the case of the more massive one) and z=1.0, respectively. This is the very first joint discovery of galaxy clusters in a sky survey combining data probing these three different wavebands.

"This survey not only shows that we can efficiently detect galaxy clusters in all these wavelengths, but also that the cluster redshifts reach easily as far as z=1, a necessary condition to follow structure evolution over an interesting cosmological time span," Hans Böhringer comments. The most distant of the two clusters is in fact seen as it was when the Universe was barely 6000 million years old, less than a half of its current age.

This result opens a new window to probe galaxy clusters to very high redshifts, which will be exploited by future missions examining different regions of the electromagnetic spectrum. One of the scientific goals of ESA's Planck mission, which is currently scanning the whole sky in microwaves, is to detect about 1000 galaxy clusters through their SZE signal imprinted on the CMB. The Euclid mission, a candidate Cosmic Vision M-class mission, is expected to detect a large number of clusters in optical and near-infrared wavelengths, thanks to its wide field of view, and to identify their redshifts. This first discovery is thus a preview of future galaxy cluster surveys and of the exciting scientific results they will bring, in the process expanding our knowledge about the evolution of cosmic structure.

Notes for editors

The two galaxy clusters detected in this study are SPT-CL J2332-5358 and SPT-CL J2342-5411, with photometric redshifts of z=0.32 and z=1.08, respectively. The photometric redshifts were obtained from optical data from the Blanco Cosmology Survey. The cluster temperatures are about T=9.3 keV (= 108 million Kelvin) and T= 4.5 keV (= 52 million Kelvin), respectively. With a mass of over 1015 solar masses, SPT-CL J2332-5358 is among the hottest and most massive clusters known; SPT-CL J2342-5411 is less massive (about 3x1014 solar masses) but is among the most distant known clusters to have been detected both through X-ray emission and SZE.

The new mosaic observing mode allows large areas of the sky, larger than the field of view of the cameras aboard the spacecraft, to be surveyed in a very efficient way. This is achieved by means of a single calibration measurement, which is performed at the beginning of the observing series and takes only up to one hour, and is then applied to all adjacent fields that are subsequently observed. This is clearly much cheaper, in terms of observing time, than the previous mode, in which the calibration measurements were performed for each field individually, consuming up to one hour for each estimate.

This new mode can be applied to observations of several astrophysical environments (for example galaxy clusters, supernova remnants, crowded fields) which require large areas of the sky to be surveyed with exposure times from a few minutes to a couple of hours.

The XMM-Newton spacecraft is controlled by the European Space Operations Centre (ESOC, Darmstadt, Germany) using ground stations at Perth (Australia) and Kourou (French Guiana). The XMM-Newton Science Operations Centre situated at ESAC in Villafranca, Spain, manages observation requests and receives XMM-Newton data. The XMM-Newton Survey Science Centre (SSC), at Leicester University, UK, processes and correlates all XMM-Newton observations with existing sky data held elsewhere in the world.

Related publications

Suhada, R., et al., "XMM-Newton detection of two clusters of galaxies with strong SPT Sunyaev-Zel'dovich effect signatures", Astronomy & Astrophysics, Vol. 514, L3, 2010. DOI: 10.1051/0004-6361/201014434

The paper appeared in May 2010 issue of Astronomy & Astrophysics.

Contacts

Róbert Suhada
Max-Planck Institute for Extraterrestrial Physics, Germany
Phone: +49-(0)89-30000-3892
Email: rsuhada@mpe.mpg.de

Hans Böhringer
Max-Planck Institute for Extraterrestrial Physics, Germany
Phone: +49-(0)89-30000-3347
Email: hxb@mpe.mpg.de

Maria Santos-Lleo, XMM-Newton Science Support Manager
XMM-Newton Science Operations Centre
Directorate of Science and Robotic Exploration
European Space Agency
Phone: +34-(0)91-8131-276
Email: Maria.Santos-Lleo@sciops.esa.int

Norbert Schartel, ESA XMM-Newton Project Scientist
Directorate of Science and Robotic Exploration European Space Agency
Phone: +34-(0)91-8131-184
Email: Norbert.Schartel@esa.int

NASA's Swift Survey finds 'Smoking Gun' of Black Hole Activation

The optical counterparts of many active galactic nuclei (circled) detected by the Swift BAT Hard X-ray Survey clearly show galaxies in the process of merging. These images, taken with the 2.1-meter telescope at Kitt Peak National Observatory in Arizona, show galaxy shapes that are either physically intertwined or distorted by the gravity of nearby neighbors. These AGN were known prior to the Swift survey, but Swift has found dozens of new ones in more distant galaxies. Credit: NASA/Swift/NOAO/Michael Koss and Richard Mushotzky (Univ. of Marylan)

Larger image | Unannotated image | Other Resolutions

Data from an ongoing survey by NASA's Swift satellite have helped astronomers solve a decades-long mystery about why a small percentage of black holes emit vast amounts of energy.

Only about one percent of supermassive black holes exhibit this behavior. The new findings confirm that black holes "light up" when galaxies collide, and the data may offer insight into the future behavior of the black hole in our own Milky Way galaxy. The study will appear in the June 20 issue of The Astrophysical Journal Letters.

The intense emission from galaxy centers, or nuclei, arises near a supermassive black hole containing between a million and a billion times the sun's mass. Giving off as much as 10 billion times the sun's energy, some of these active galactic nuclei (AGN) are the most luminous objects in the universe. They include quasars and blazars.

"Theorists have shown that the violence in galaxy mergers can feed a galaxy's central black hole," said Michael Koss, the study's lead author and a graduate student at the University of Maryland in College Park. "The study elegantly explains how the black holes switched on."

Until Swift's hard X-ray survey, astronomers never could be sure they had counted the majority of the AGN. Thick clouds of dust and gas surround the black hole in an active galaxy, which can block ultraviolet, optical and low-energy, or soft X-ray, light. Infrared radiation from warm dust near the black hole can pass through the material, but it can be confused with emissions from the galaxy's star-forming regions. Hard X-rays can help scientists directly detect the energetic black hole.

Since 2004, the Burst Alert Telescope (BAT) aboard Swift has been mapping the sky using hard X-rays.

"Building up its exposure year after year, the Swift BAT Hard X-ray Survey is the largest, most sensitive and complete census of the sky at these energies," said Neil Gehrels, Swift's principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Md.

The survey, which is sensitive to AGN as far as 650 million light-years away, uncovered dozens of previously unrecognized systems.

"The Swift BAT survey is giving us a very different picture of AGN," Koss said. The team finds that about a quarter of the BAT galaxies are in mergers or close pairs. "Perhaps 60 percent of these galaxies will completely merge in the next billion years. We think we have the 'smoking gun' for merger-triggered AGN that theorists have predicted."

Other members of the study team include Richard Mushotzky and Sylvain Veilleux at the University of Maryland and Lisa Winter at the Center for Astrophysics and Space Astronomy at the University of Colorado in Boulder.

"We've never seen the onset of AGN activity so clearly," said Joel Bregman, an astronomer at the University Michigan, Ann Arbor, who was not involved in the study. "The Swift team must be identifying an early stage of the process with the Hard X-ray Survey."

Swift, launched in November 2004, is managed by Goddard. It was built and is being operated in collaboration with Penn State, the Los Alamos National Laboratory in New Mexico, and General Dynamics in Falls Church, Va.; the University of Leicester and Mullard Space Sciences Laboratory in the United Kingdom; Brera Observatory and the Italian Space Agency in Italy; plus additional partners in Germany and Japan.

This simulation follows the collision of two spiral galaxies that harbor giant black holes. The merger stirs up gas in both galaxies. Infalling gas "switches on" the black hole and creates an active galactic nucleus (AGN). Credit: Volker Springel and Tiziana Di Matteo (Max Planck Institute for Astrophysics), Lars Hernquist (Harvard Univ.) Download Video

See the original animation at: http://web.phys.cmu.edu/~tiziana/BHGrow/

Click here for multimedia related to the May 26, 2010, NASA briefing on Swift's findings.

Francis Reddy

NASA's Goddard Space Flight Center

Astronomers Discover New Star-Forming Regions in Milky Way

Artist's Conception of the Milky Way

CREDIT: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

Astronomers studying the Milky Way have discovered a large number of previously-unknown regions where massive stars are being formed. Their discovery provides important new information about the structure of our home Galaxy and promises to yield new clues about the chemical composition of the Galaxy.

"We can clearly relate the locations of these star-forming sites to the overall structure of the Galaxy. Further studies will allow us to better understand the process of star formation and to compare the chemical composition of such sites at widely different distances from the Galaxy's center," said Thomas Bania, of Boston University.

Bania worked with Loren Anderson of the Astrophysical Laboratory of Marseille in France, Dana Balser of the National Radio Astronomy Observatory (NRAO), and Robert Rood of the University of Virginia. The scientists presented their findings to the American Astronomical Society's meeting in Miami, Florida.

The star-forming regions the astronomers sought, called H II regions, are sites where hydrogen atoms are ionized, or stripped of their electrons, by the intense radiation of the massive, young stars. To find these regions hidden from visible-light detection by the Milky Way's gas and dust, the researchers used infrared and radio telescopes.

"We found our targets by using the results of infrared surveys done with NASA's Spitzer Space Telescope and of surveys done with the National Science Foundation's (NSF) Very Large Array (VLA) radio telescope," Anderson said. "Objects that appear bright in both the Spitzer and VLA images we studied are good candidates for H II regions," he explained.

The astronomers then used the NSF's giant Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, an extremely sensitive radio telescope. With the GBT, they were able to detect specific radio frequencies emitted by electrons as they recombined with protons to form hydrogen. This evidence of recombination confirmed that the regions contained ionized hydrogen and thus are H II regions.

Further analysis allowed the astronomers to determine the locations of the H II regions. They found concentrations of the regions at the end of the Galaxy's central bar and in its spiral arms. Their analysis also showed that 25 of the regions are farther from the Galaxy's center than the Sun.

"Finding the ones beyond the solar orbit is important, because studying them will provide important information about the chemical evolution of the Galaxy. There is evidence that the abundance of heavy elements changes with increasing distance from the Galactic center. We now have many more objects to study and improve our understanding of this effect," Bania said.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Contact:

Dave Finley, Public Information Officer
Socorro, NM
(575) 835-7302
dfinley@nrao.edu

Astronomers Discover Clue to Origin of Milky Way Gas Clouds

Artist's conception shows Milky Way regions studied, with hydrogen clouds more abundant in region above area where central bar merges with spiral arm. Bright point at bottom center is location of our Solar System. CREDIT:Bill Saxton, NRAO/AUI/NSF

JPEG File (389 KB) | TIFF File (10.4 MB)

A surprising discovery that hydrogen gas clouds found in abundance in and above our Milky Way Galaxy have preferred locations has given astronomers a key clue about the origin of such clouds, which play an important part in galaxy evolution.

"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 H. Alyson Ford of the University of Michigan, whose Ph.D thesis research from Swinburne University formed the basis for this result. The team, consisting of Ford and collaborators Felix J. Lockman, of the National Radio Astronomy Observatory (NRAO), and Naomi Mclure-Griffiths of CSIRO Astronomy and Space Science, presented their findings to the American Astronomical Society's meeting in Miami, Florida.

The astronomers studied gas clouds in two distinct regions of the Galaxy. The clouds they studied are between 400 and 15,000 light-years outside the disk-like plane of the Galaxy. The disk contains most of the Galaxy's stars and gas, and is surrounded by a "halo" of gas more distant than the clouds the astronomers studied.

"These clouds were first detected with the National Science Foundation's Robert C. Byrd Green Bank Telescope, and are quite puzzling. They are in a transitional area between the disk and the halo, and their origin has been uncertain," Lockman explained. The research team used data from the Galactic All-Sky Survey, made with CSIRO's Parkes radio telescope in Australia.

When the astronomers compared the observations of the two regions, they saw that one region contained three times as many hydrogen clouds as the other. In addition, that region's clouds are, on average, twice as far above the Galaxy's plane.

The dramatic difference, they believe, is because the region with more clouds lies near the tip of the Galaxy's central "bar," where the bar merges with a major spiral arm. This is an area of intense star formation, containing many young stars whose strong winds can propel gas away from the region. The most massive stars also will explode as supernovae, blasting material outward. In the other region they studied, star formation activity is more sparse.

"The properties of these clouds show clearly that they originated as part of the Milky Way's disk, and are a major component of our Galaxy. Understanding these clouds is important in understanding how material moves between the Galaxy's disk and its halo, a critical process in the evolution of galaxies," Lockman said.

The clouds consist of neutral hydrogen gas, with an average mass equal to that of about 700 Suns. Their sizes vary greatly, but most are about 200 light-years across. The astronomers studied about 650 such clouds in the two widely-separated regions of the Galaxy.

The Parkes Radio Telescope is part of the Australia Telescope, which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Contact

Dave Finley, Public Information Officer

Socorro, NM

(575) 835-7302

dfinley@nrao.edu

Bright galaxies like to stick together

Astronomers using the European Space Agency's Herschel telescope have discovered that the brightest galaxies tend to be in the busiest parts of the Universe. This crucial piece of information will enable theorists to fix up their theories of galaxy formation. For over a decade, astronomers have been puzzled by some strange, bright galaxies in the distant Universe which appear to be forming stars at phenomenal rates. These galaxies are very hard to explain with conventional theories of galaxy formation. One important question has been the environments in which these galaxies are located, such as how close together they are. The Herschel Space Observatory, with its ability for very sensitive mapping over wide areas, has been able to see thousands of these galaxies and identify their location, showing for the first time that these galaxies are packed closely together in the centre of large galaxy clusters.

A project using the UK-led SPIRE instrument on board Herschel has been surveying large areas of the sky, currently totalling 15 square degrees – around 60 times the size of the Full Moon. The two regions mapped so far are in the constellations of Ursa Major and Draco, well away from the confusion of our own Galaxy. Galaxies which are brightest at Herschel’s far-infrared wavelengths are typically seen as they were around 10 billion years ago, the light having been travelling towards us since that time.

Hershcel's view of a patch of sky in the constellation of Ursa Major. Almost every one of the thousands of dots is a distant galaxy. Image credit: ESA / SPIRE / HerMES

The false-colour image above shows a small portion of the sky observed by Herschel. Almost every point of light is an entire galaxy, each containing billions of stars. The colours represent the far-infrared wavelengths measured by Herschel, with redder galaxies either being further away or containing colder dust, while brighter galaxies are forming stars more vigorously. While at a first glance the galaxies look to be scattered randomly over the image, in fact they are not. A closer look will reveals that there are regions which have more galaxies in, and regions that have fewer. This clustering of galaxies through space provides information about the way they have interacted over the history of the Universe.

The Antennae Galaxies as seen in the far-infrared by Herschel (left), and in visible light by the Hubble Space Telescope (right). The areas with most star formation are bright in the Herschel image, but hidden by dust in the Hubble image. Image credit: ESA / PACS / SHINING / U. Klaas & M. Nielbock, MPIA.

Herschel sees material that cannot be seen at visible wavelengths, namely cold gas and dust between the stars. This is well illustrated by looking at much closer galaxies, which can be seen in more detail. The Antennae Galaxies, lying a mere 50 million light years away, are actually two galaxies which are in the process of colliding, and were observed as part of a different observing programme. Herschel does not see the light from stars, but the clouds of dust within which new stars are forming. The collision of these galaxies has caused a surge in star formation, but such collisions are relatively rare in the Universe today. Billions of years ago, however, when galaxies were much more tightly packed, such events were much more common.

Despite the new window on the Universe afforded by the far-infrared light, Herschel is still not seeing the full picture. Three quarters of the matter in our Universe is made up of mysterious “dark matter”, which does not shine at all. Since we cannot see dark matter, we do not yet know what it is made of, but we can measure its effect on the matter around it. Although it does not emit or absorb light, dark matter does interact with the rest of the Universe through gravity, gradually pulling groups of galaxies together into huge clusters over the course of billions of years. While many computer simulations exist of how this occurs, the ability to measure this at different times through the history of the Universe allows astronomers to compare the simulations with real measurements.

These latest results from Herschel, part of the “HerMES” key programme, have shown that the bright galaxies detected with the SPIRE instrument preferentially occupy regions of the Universe that contain more dark matter. This seems to be especially true about 10 billion years ago, when these galaxies were forming stars at a much higher rate than most galaxies are today.

Our Galaxy, the Milky Way, resides on the suburbs of a large supercluster centred about 60 million light years away. The neighbouring supercluster of galaxies to us is around 300 million light years away. By comparison, 10 billion years ago galaxies were only 20 to 30 million light years apart on average. Their proximity means that many of the galaxies will eventually collide with one another. It is these collisions that stirs up the gas and dust in the galaxies and causes the rapid bouts of star formation. Professor Asantha Cooray, of the University of California, is one of the HerMES astronomers leading this investigation, and he commented on the latest HerMES results: "Thanks to the superb resolution and sensitivity of the SPIRE instrument on Herschel, we managed to map in detail the spatial distribution of massively starforming galaxies in the early universe. All indications are that these galaxies are busy. They are crashing, merging, and possibly settling down at centres of large dark matter halos."

It has required the sensitivity and resolution of Herschel to be able to identify the brightest galaxies and establish the way in which they are clustering. Dr Lingyu Wang, of the University of Sussex, said "we have known for a long time that environment plays an important role in shaping galaxies' evolution. With Herschel, we are able to pierce through huge amounts of dust and study the impact of the environment right from the birth of these massive galaxies forming stars at colossal rates. This is allowing us to witness the active past of today's dead elliptical galaxies at times when they were in rich environments."

Professor Seb Oliver, of the University of Sussex, who co-leads the HerMES project, presented this result last week at the Herschel First Results Symposium in the Netherlands. Professor Oliver said "this result from Asantha's team is fantastic, it is just the kind of thing we were hoping for from Herschel and was only possible because we can see so many thousands of galaxies, it will certainly give the theoretician's something to chew over".

This work, conducted as part of the Herschel Multi-tiered Extragalactic Survey (HerMES) Key Project of the Herschel mission, will be published in the international science journal “Astronomy & Astrophysics” in a special issue dedicated to the first science results from Herschel. The project will continue to collect more images over larger areas of the sky in order to build up a more complete picture of how galaxies have evolved and interacted over the past 10-12 billion years.

Supermassive Black Holes May Frequently Roam Galaxy Centers

A team of astronomy researchers at Florida Institute of Technology and Rochester Institute of Technology in the United States and University of Sussex in the United Kingdom, find that the supermassive black hole (SMBH) at the center of the most massive local galaxy (M87) is not where it was expected. Their research, conducted using the Hubble Space Telescope (HST), concludes that the SMBH in M87 is displaced from the galaxy center. The most likely cause for this SMBH to be off center is a previous merger between two older, less massive, SMBHs. The iconic M87 jet may have pushed the SMBH away from the galaxy center, say researchers. The research is being presented today at the 216th meeting of the American Astronomical Society in Miami. It will also be published in The Astrophysical Journal Lettters. For more information about this research, visit: http://www.fit.edu/newsroom/news/3917/

supermassive_black_holes_may_frequently_roam_galaxy_centers/

About this image: Astronomers find that the supermassive black hole at the center of the most massive local galaxy (M87) is not where it was expected. Their research, conducted using the Hubble Space Telescope, concludes that the supermassive black hole in M87 is displaced from the galaxy center.

At right is a large-scale image of galaxy M87 taken in 1998 with Hubble's Wide-Field Planetary Camera 2. The two images at left show an image taken in 2006 with Hubble's Advanced Camera for Surveys. The position of the supermassive black hole is indicated by the black dot in the lower left panel, and a knot in the jet (HST-1), which was flaring in 2006, is also indicated on this panel. The red dot indicates the center of the galaxy's light distribution, which is offset from the position of the black hole by about 22 light-years.

Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Biretta, W. Sparks, and F.D. Macchetto (STScI), and E. Perlman (Florida Institute of Technology)

For more information, contact:

Karen Rhine
Florida Institute of Technology Office of Communications
321-674-8964
krhine@fit.edu

Daniel Batcheldor
Florida Institute of Technology, Melbourne, Fla.
321-674-7717
dbatcheldor@fit.edu

Eric Perlman
Florida Institute of Technology, Melbourne, Fla.
321-674-7741
eperlman@fit.edu

Nearby Black Hole is Feeble and Unpredictable

The large image here shows an optical view, with the Digitized Sky Survey, of the Andromeda Galaxy, otherwise known as M31. The inset shows Chandra images of a small region in the center of Andromeda. The image on the left shows a sum of Chandra images taken before January 2006 and the image on the right shows a sum of images taken after January 2006. Before 2006, three X-ray sources are clearly visible, including one faint source close to the center of the image. After 2006, a fourth source, called M31*, appears just below and to the right of the central source, produced by material falling onto the supermassive black hole in M31. Credit: X-ray (NASA/CXC/SAO/Li et al.), Optical (DSS)

Miami, FL - For over 10 years, NASA's Chandra X-ray Observatory has repeatedly observed the Andromeda Galaxy for a combined total of nearly one million seconds. This unique data set has given astronomers an unprecedented view of the nearest supermassive black hole outside our own Galaxy.

Astronomers think that most galaxies - including the Milky Way - contain giant black holes at their cores that are millions of times more massive than the Sun. At a distance of just under 3 million light years from Earth, Andromeda (also known as M31) is relatively close and provides an opportunity to study its black hole in great detail.

Just like the one in the center of the Milky Way, the black hole in Andromeda is surprisingly quiet. In fact, Andromeda's black hole, known as M31*, is ten to one hundred thousand times fainter in X-ray light that astronomers might expect given the reservoir of gas around it.

"The black holes in both Andromeda and the Milky Way are incredibly feeble," said Zhiyuan Li of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass. "These two 'anti-quasars' provide special laboratories for us to study some of the dimmest type of accretion even seen onto a supermassive black hole."

The decade-long study by Chandra reveals that M31* was in a very dim, or quiet, state before 2006. However, on January 6, 2006, the black hole became more than a hundred times brighter, suggesting an outburst of X-rays. This was the first time such an event had been seen from a supermassive black hole in the nearby, local universe.

After the outburst, M31* entered another relatively dim state, but was almost ten times brighter on average than before 2006. The outburst suggests a relatively high rate of matter falling onto M31* followed by a smaller, but still significant rate.

"We have some ideas about what's happening right around the black hole in Andromeda, but the truth is we still don't really know the details," said Christine Jones, also of the CfA.

The overall brightening since 2006 could be caused by M31* capturing winds from an orbiting star, or by a gas cloud that spiraled into the black hole. The increase in the rate of material falling towards the black hole is thought to drive an X-ray brightening of a relativistic jet.

The cause of the outburst in 2006 is even less clear, but it could be due to a sudden release of energy, such as magnetic fields in a disk around the black hole that suddenly connect and become more powerful.

"It's important to figure out what's going on here because the accretion of matter onto these black holes is one of the most fundamental processes governing the evolution of galaxies," said Li who presented these results at the 216th meeting of the American Astronomical Society meeting in Miami, FL.

These results imply that the feeble, but erratic behavior of the black hole in the Milky Way may be typical for present-day supermassive black holes.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

Megan Watzke
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-496-7998
mwatzke@cfa.harvard.edu

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

WISE Makes Progress on its Space Rock Catalog

This animation shows asteroids and comets observed so far by NASA's Wide-field Infrared Survey Explorer, or WISE. View animation (mov)

NASA's Wide-field Infrared Survey Explorer, or WISE, is busy surveying the landscape of the infrared sky, building up a catalog of cosmic specimens -- everything from distant galaxies to "failed" stars, called brown dwarfs.

Closer to home, the mission is picking out an impressive collection of asteroids and comets, some known and some never seen before. Most of these hang out in the Main Belt between Mars and Jupiter, but a small number are near-Earth objects -- asteroids and comets with orbits that pass within about 48 million kilometers (30 million miles) of Earth's orbit. By studying a small sample of near-Earth objects, WISE will learn more about the population as a whole. How do their sizes differ, and how many objects are dark versus light?

"We are taking a census of a small sample of near-Earth objects to get a better idea of how they vary," said Amy Mainzer, the principal investigator of NEOWISE, a program to catalog asteroids seen with WISE.

So far, the mission has observed more than 60,000 asteroids, both Main Belt and near-Earth objects. Most were known before, but more than 11,000 are new.

"Our data pipeline is bursting with asteroids," said WISE Principal Investigator Ned Wright of UCLA. "We are discovering about a hundred a day, mostly in the Main Belt."

About 190 near-Earth asteroids have been observed to date, of which more than 50 are new discoveries. All asteroid observations are reported to the NASA-funded International Astronomical Union's Minor Planet Center, a clearinghouse for data on all solar system bodies at the Smithsonian Astrophysical Observatory in Cambridge, Mass.

"It's a really exciting time for asteroid science," said Tim Spahr, who directs the Minor Planet Center. "WISE is another tool to add to our tool belt of instruments to discover and study the asteroid population."

A network of ground-based telescopes follows up and confirms the WISE finds, including the NASA-funded University of Arizona Spacewatch and Catalina Sky Survey projects, both near Tucson, Ariz., and the NASA-funded Magdalena Ridge Observatory near Socorro, N.M.

Some of the near-Earth asteroids detected so far are visibly dark, but it's too early to say what percentage. The team needs time to properly analyze and calibrate the data. When results are ready, they will be published in a peer-reviewed journal. WISE has not found an asteroid yet that would be too dark for detection by visible-light telescopes on the ground.

"We're beginning the process of sorting through all the objects we're finding so we can learn more about their properties," said Mainzer. "How many are big or small, or light versus dark?"

WISE will also study Trojans, asteroids that run along with Jupiter in its orbit around the sun and travel in two packs -- one in front of and one behind the gas giant. It has seen more than 800, and by the end of the mission, should have observed about half of all 4,500 known Trojans. The results will address dueling theories about how the outer planets evolved.

With its infrared vision, WISE is good at many aspects of asteroid watching. First, infrared light gives a better estimate of an asteroid's size. Imagine a light, shiny rock lying next to a bigger, dark one in the sunshine. From far away, the rocks might look about the same size. That's because they reflect about the same amount of visible sunlight. But, if you pointed an infrared camera at them, you could tell the dark one is bigger. Infrared light is related to the heat radiated from the rock itself, which, in turn, is related to its size.

A second benefit of infrared is the ability to see darker asteroids. Some asteroids are blacker than coal and barely reflect any visible light. WISE can see their infrared glow. The mission isn't necessarily hunting down dark asteroids in hiding, but collecting a sample of all different types. Like a geologist collecting everything from pumice to quartz, WISE is capturing the diversity of cosmic rocks in our solar neighborhood.

In the end, WISE will provide rough size and composition profiles for hundreds of near-Earth objects, about 100 to 200 of which will be new.

WISE has also bagged about a dozen new comets to date. The icy cousins to asteroids are easy for the telescope to spot because, as the comets are warmed by the sun, gas and dust particles blow off and glow with infrared light. Many of the comets found by WISE so far are so-called long-period comets, meaning they spend billions of years circling the sun in the frigid hinterlands of our solar system, before they are shuttled into the inner, warmer parts. Others are termed short-period comets -- they spend most of their lives hanging around the space near Jupiter, occasionally veering into the space closer to the terrestrial planets. WISE's measurements of these snowy dirtballs will allow scientists to study their size, composition and density. Measurements of the comets' orbits will help explain what kicks these objects out of their original, more distant orbits and in toward the sun.

WISE will complete one-and-a-half scans of the sky in October of this year. Visit http://wise.astro.ucla.edu to see selected WISE images released so far.

JPL manages WISE for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. More information is online at http://www.nasa.gov/wise and http://wise.astro.ucla.edu .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

Out of Whack Planetary System Offers Clues to a Disturbed Past

This is an artist's illustration of the Upsilon Andromedae A planetary system, where three Jupiter-type planets orbit the yellow-white star Upsilon Andromedae A. Astronomers have recently discovered that not all planets orbit this star in the same plane, as the major planets in our solar system orbit the Sun. The orbits of two of the planets are inclined by 30 degrees with respect to each other. Such a strange orientation has never before been seen in any other planetary system. This surprising finding will impact theories of how planetary systems form and evolve, say researchers. It suggests that some violent events can happen to disrupt planets' orbits after a planetary system forms. The discovery was made by joint observations with the Hubble Space Telescope, the Hobby-Eberly Telescope, and other ground-based telescopes. Illustration Credit: NASA, ESA, and A. Feild (STScI). Science Credit: NASA, ESA, and B. McArthur (The University of Texas at Austin McDonald Observatory)

This is an artist's illustration that compares the solar system with the Upsilon Andromedae system. Astronomers have recently discovered that not all planets orbit the bright yellow-white star Upsilon Andromedae in the same plane, as the major planets in our solar system orbit the Sun. The orbits of two of the planets, c and d, are inclined by 30 degrees with respect to each other. Such a strange orientation has never before been seen in any other planetary system. This surprising finding will impact theories of how planetary systems form and evolve, say researchers. It suggests that some violent events can happen to disrupt planets' orbits after a planetary system forms. The discovery was made by joint observations with the Hubble Space Telescope, the Hobby-Eberly Telescope, and other ground-based telescopes. Illustration Credit: NASA, ESA, and A. Feild (STScI). Science Credit: NASA, ESA, and B. McArthur (The University of Texas at Austin McDonald Observatory)

Astronomers are reporting today the discovery of a planetary system way out of tilt, where the orbits of two planets are at a steep angle to each other. This surprising finding will impact theories of how multi-planet systems evolve, and it shows that some violent events can happen to disrupt planets' orbits after a planetary system forms, say researchers.

"The findings mean that future studies of exoplanetary systems will be more complicated. Astronomers can no longer assume all planets orbit their parent star in a single plane," says Barbara McArthur of The University of Texas at Austin's McDonald Observatory.

McArthur and her team used data from the Hubble Space Telescope, the giant Hobby-Eberly Telescope, and other ground-based telescopes combined with extensive modeling to unearth a landslide of information about the planetary system surrounding the nearby star Upsilon Andromedae.

McArthur reported these findings in a press conference today at the 216th meeting of the American Astronomical Society in Miami, along with her collaborator Fritz Benedict, also of McDonald Observatory, and team member Rory Barnes of the University of Washington. The work also will be published in the June 1 edition of the Astrophysical Journal.

For just over a decade, astronomers have known that three Jupiter-type planets orbit the yellow-white star Upsilon Andromedae. Similar to our Sun in its properties, Upsilon Andromedae lies about 44 light-years away. It's a little younger, more massive, and brighter than the Sun.

Combining fundamentally different, yet complementary, types of data from Hubble and ground-based telescopes, McArthur's team has determined the exact masses of two of the three known planets, Upsilon Andromedae c and d. Much more startling, though, is their finding that not all planets orbit this star in the same plane. The orbits of planets c and d are inclined by 30 degrees with respect to each other. This research marks the first time that the "mutual inclination" of two planets orbiting another star has been measured. And, the team has uncovered hints that a fourth planet, e, orbits the star much farther out.

"Most probably Upsilon Andromedae had the same formation process as our own solar system, although there could have been differences in the late formation that seeded this divergent evolution," McArthur said. "The premise of planetary evolution so far has been that planetary systems form in the disk and remain relatively co-planar, like our own system, but now we have measured a significant angle between these planets that indicates this isn't always the case."

Until now the conventional wisdom has been that a big cloud of gas collapses down to form a star, and planets are a natural byproduct of leftover material that forms a disk. In our solar system, there's a fossil of that creation event because all of the eight major planets orbit in nearly the same plane. The outermost dwarf planets like Pluto are in inclined orbits, but these have been modified by Neptune's gravity and are not embedded deep inside the Sun's gravitational field.

Several different gravitational scenarios could be responsible for the surprisingly inclined orbits in Upsilon Andromedae, "Possibilities include interactions occurring from the inward migration of planets, the ejection of other planets from the system through planet-planet scattering, or disruption from the parent star's binary companion star, Upsilon Andromedae B," McArthur said.

Barnes, an expert in the dynamics of extrasolar planetary systems, added, "Our dynamical analysis shows that the inclined orbits probably resulted from the ejection of an original member of the planetary system. However, we don't know if the distant stellar companion forced that ejection, or if the planetary system itself formed in such a way that some original planets were ejected. Furthermore, we find that the revised configuration still lies right on the precipice of instability: The planets pull on each other so strongly that they are almost able to throw each other out of the system."

The two different types of data combined in this research were astrometry from the Hubble Space Telescope and radial velocity from ground-based telescopes.

Astrometry is the measurement of the positions and motions of celestial bodies. McArthur's group used one of the Fine Guidance Sensors (FGSs) on the Hubble telescope for the task. The FGSs are so precise that they can measure the width of a quarter in Denver from the vantage point of Miami. It was this precision that was used to trace the star's motion on the sky caused by its surrounding — and unseen — planets.

Radial velocity makes measurements of the star's motion on the sky toward and away from Earth. These measurements were made over a period of 14 years using ground-based telescopes, including two at McDonald Observatory and others at Lick, Haute-Provence, and Whipple Observatories. The radial velocity provides a long baseline of foundation observations, which enabled the shorter duration, but more precise and complete, Hubble observations to better define the orbital motions.

The fact that the team determined the orbital inclinations of planets c and d allowed them to calculate the exact masses of the two planets. The new information told us that our view as to which planet is heavier has to be changed. Previous minimum masses for the planets given by radial velocity studies put the minimum mass for planet c at 2 Jupiters and for planet d at 4 Jupiters. The new, exact masses, found by astrometry are 14 Jupiters for planet c and 10 Jupiters for planet d.

"The Hubble data show that radial velocity isn't the whole story," Benedict said. "The fact that the planets actually flipped in mass was really cute."

The 14 years of radial velocity information compiled by the team uncovered hints that a fourth, long-period planet may orbit beyond the three now known. There are only hints about that planet because it's so far out that the signal it creates does not yet reveal the curvature of an orbit. Another missing piece of the puzzle is the inclination of the innermost planet, b, which would require precision astrometry 1,000 times greater than Hubble's, a goal attainable by a space mission optimized for interferometry.

The team's Hubble data also confirmed Upsilon Andromedae's status as a binary star. The companion star is a red dwarf less massive and much dimmer than the Sun.

"We don't have any idea what its orbit is," Benedict said. "It could be very eccentric. Maybe it comes in very close every once in a while. It may take 10,000 years." Such a close pass by the secondary star could gravitationally perturb the orbits of the planets.

CONTACT

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

Rebecca Johnson
McDonald Observatory, The University of Texas at Austin
512-475-6763
rjohnson@astro.as.utexas.edu


For additional information, contact:

Barbara McArthur
McDonald Observatory
The University of Texas at Austin
512-471-3411
mca@astro.as.utexas.edu

Fritz Benedict
McDonald Observatory
The University of Texas at Austin
512-471-3448
fritz@astro.as.utexas.edu

Rory Barnes
Department of Astronomy
The University of Washington, Seattle
206-543-8979
rory@astro.washington.edu

N49: Stellar Shrapnel Seen in Aftermath of Explosion

N49

Credit: X-ray (NASA/CXC/Penn State/S.Park et al.);

Optical: NASA/STScI/UIUC/Y.H.Chu & R.Williams et al

JPEG (678.1 kb)

Tiff (14.2 MB)

PS (14.8 MB)

Download Desktop

High-Quality Prints

More Images

Zoom-In (flash)

This beautiful composite image shows N49, the aftermath of a supernova explosion in the Large Magellanic Cloud. A new long observation from NASA's Chandra X-ray Observatory, shown in blue, reveals evidence for a bullet-shaped object being blown out of a debris field left over from an exploded star.

In order to detect this bullet, a team of researchers led by Sangwook Park of Penn State University used Chandra to observe N49 for over 30 hours. This bullet can be seen in the bottom right hand corner of the image (roll your mouse over the image above) and is rich in silicon, sulphur and neon. The detection of this bullet shows that the explosion that destroyed the star was highly asymmetric.

The bullet is traveling at a high speed of about 5 million miles an hour away from a bright point source in the upper left part of N49. This bright source may be a so-called soft gamma ray repeater (SGR), a source that emits bursts of gamma rays and X-rays. A leading explanation for these objects is that they are neutron stars with extremely powerful magnetic fields. Since neutron stars are often created in supernova explosions, an association between SGRs and supernova remnants is not unexpected. This case is strengthened by the apparent alignment between the bullet's path and the bright X-ray source. However, the new Chandra data also shows that the bright source is more obscured by gas than expected if it really lies inside the supernova remnant. In other words, it is possible that the bright X-ray source actually lies beyond the remnant and is projected along the line of sight. Another possible bullet is located on the opposite side of the remnant, but it is harder to see in the image because it overlaps with the bright emission - described below - from the shock-cloud interaction.

Optical data from the Hubble Space Telescope (yellow and purple) shows bright filaments where the shock wave generated by the supernova is interacting with the densest regions in nearby clouds of cool, molecular gas.

Using the new Chandra data, the age of N49 -- as it appears in the image -- is thought to be about 5,000 years and the energy of the explosion is estimated to be about twice that of an average supernova. These preliminary results suggest that the original explosion was caused by the collapse of a massive star.

Fast Facts for N49:

Scale: Image is 1.63 arcmin (about 75 light years) across
Category: Supernovas & Supernova Remnants
Coordinates: (J2000) RA 05h 25m 25.00s | Dec -65º 59' 22.00"
Constellation: Dorado
Observation Date: 4 pointings from Jul 18 to Sep 19, 2009
Observation Time: 43 hours (1 day 19 hours)
Obs. ID: 10123; 10806-10808
Color Code: X-ray (Blue); Optical (Yellow, Purple)
Instrument: ACIS
Distance Estimate: About 160,000 light years

WISE Telescope has Heart and Soul

The Heart and Soul nebulae are seen in this infrared mosaic from NASA's Wide-field Infrared Survey Explorer, or WISE. Image credit: NASA/JPL-Caltech/UCLA. Full resolution jpeg (26 Mb)

PASADENA, Calif. -- NASA's Wide-field Infrared Survey Explorer, or WISE, has captured a huge mosaic of two bubbling clouds in space, known as the Heart and Soul nebulae. The space telescope, which has completed about three-fourths of its infrared survey of the entire sky, has already captured nearly one million frames like the ones making up this newly released mosaic.

"This new image demonstrates the power of WISE to capture vast regions," said Ned Wright, the mission's principal investigator at UCLA, who presented the new picture today at the American Astronomical Society meeting in Miami. "We're looking north, south, east and west to map the whole sky."

The picture is online at http://www.nasa.gov/mission_pages/WISE/news/wise20100524.html.

The Heart nebula is named after its resemblance to a human heart; the nearby Soul nebula happens to resemble a heart too, but only the symbolic kind with two lobes. The nebulae, which lie about 6,000 light-years away in the constellation Cassiopeia, are both massive star-making factories, marked by giant bubbles blown into surrounding dust by radiation and winds from the stars. The infrared vision of WISE allows it to see into the cooler and dustier crevices of clouds like these, where gas and dust are just beginning to collect into new stars.

The new image was captured as WISE circled over Earth's poles, scanning strips of the sky. It is stitched together from 1,147 frames, taken with a total exposure time of three-and-a-half hours.

The mission will complete its first map of the sky in July 2010. It will then spend the next three months surveying much of the sky a second time, before the solid-hydrogen coolant needed to chill its infrared detectors runs dry. The first installment of the public WISE catalog will be released in summer 2011.

About 960,000 WISE images have been beamed down from space to date. Some show ethereal star-forming clouds, while others reveal the ancient light of very remote, powerful galaxies. And many are speckled with little dots that are asteroids in our solar system. So far, the mission has observed more than 60,000 asteroids, most of which lie in the main belt, orbiting between Mars and Jupiter. About 11,000 of these objects are newly discovered, and about 50 of them belong to a class of near-Earth objects, which have paths that take them within about 48 million kilometers (30 million miles) of Earth’s orbit.

One goal of the WISE mission is to study asteroids throughout our solar system and to find out more about how they vary in size and composition. Infrared helps with this task because it can get better size measurements of the space rocks than visible light.

"Infrared will help us understand more about the sizes, properties and origins of asteroids near and far," said Amy Mainzer, the principal investigator of NEOWISE, a program to study and catalog asteroids seen by WISE (the acronym comes from combining near-Earth object, or NEO, with WISE).

WISE will also study the Trojans, asteroids that run along with Jupiter in its orbit around the sun in two packs -- one in front of and one behind the gas giant. It has seen more than 800 of these objects, and by the end of the mission, should have observed about half of all 4,500 known Trojans. The results will address dueling theories about how the outer planets evolved.

"WISE is the first survey capable of observing the two clouds in a uniform way, and this will provide valuable insight into the early solar system," said astronomer Tommy Grav of Johns Hopkins University, Baltimore, Md., who presented the information today at the astronomy meeting.

Comets have also made their way into WISE images, with more than 72 observed so far, about a dozen of them new. WISE is taking a census of the types of orbits comets ride in. The data will help explain what kicks comets out of their original, more distant orbits and in toward the sun.

JPL manages WISE for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. More information is online at http://www.nasa.gov/wise and http://wise.astro.ucla.edu .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

The case of the grown-up galaxy

It seems, early on its life, our Universe was a place of extremes.

That’s the conclusion scientists are drawing from new infrared observations of a very distant, unusually bright and massive elliptical galaxy.

This galaxy [in the white square above] was spotted 10 billion light years away, and gives us a glimpse of what the Universe looked like when it was only about one-quarter of its current age.

Measurements show that the galaxy is as large and equally dense as elliptical galaxies that can be found much closer to us. Coupled with recent observations by a different research team - which found a very compact and extremely dense elliptical galaxy in the early Universe - the findings deepen the puzzle over how ‘fully grown’ galaxies can exist alongside seemingly ‘immature’ compact galaxies in the young Universe.

‘What our observations show is that alongside these compact galaxies were other ellipticals that were anything up to 100 times less dense and between two and five times larger – essentially ‘fully grown’ – and much more like the ellipticals we see in the local Universe around us,’ explains Michele Cappellari of Oxford University’s Department of Physics, an author of a report of the research in The Astrophysical Journal Letters.

‘The mystery is how these two different extremes, ‘grown up’ and seemingly ‘immature’ ellipticals, co-existed so early on in the evolution of the Universe.’

Elliptical galaxies, which are regular in shape, can be over ten times as massive as spiral galaxies such as our own Milky Way and contain stars which formed over 10 billion years ago. One way of checking the density of such galaxies is to use the infrared spectrum they emit to measure the spread of the velocities of their stars, which has to balance the pull of gravity.

Measurements of a distant compact elliptical galaxy have shown that its stars were dispersing at a velocity of about 500 km per second, consistent with its size but unknown in local galaxies.

The new study, using the 8.3-m Japanese Subaru telescope in Hawaii, found a ‘fully grown’ elliptical with stars dispersing at a velocity of lower than 300 km per second, much more like similar galaxies close to us.

‘Our next step is to use the Subaru telescope to find the relative proportion of these two extremes, fully grown and compact ellipticals, and see how they fit in with the timeline of the evolution of the young Universe,’ Michele tells us. ‘Hopefully this will give us new insights into solving this cosmic puzzle.’

Pete Wilton

Dr Michele Cappellari is based at Oxford’s Department of Physics.

The research was conducted by an international team led by Masato Onodera, CEA/Saclay, France.

Helium pair have regular violent flare ups

Images of KL Dra when it was in a low brightness state (left hand images) and a high brightness state (right hand images). The upper images were taken using the Liverpool Telescope to study the system in visible light while the lower images were made using the Swift satellite to observe the system in ultraviolet light. The position of KL Dra is located between the white lines. The galaxy in the mid-upper area of the image is a distant galaxy as is the fuzzy object close to KL Dra. Credit: Upper Images - Liverpool Telescope/Gavin Ramsay, lower Images - Swift Satellite-UVOT/Gavin Ramsay . http://www.arm.ac.uk/~gar/kldra-opt-uv-low-high.jpg

A team of astronomers led by Dr Gavin Ramsay of Armagh Observatory have spotted violent eruptions from an interacting pair of stars that orbit around each other every 25 minutes. Unusually, these outbursts take place at regular and predictable intervals, erupting every two months. The new observations were made using the fully robotic Liverpool Telescope sited in the Canary Islands and the orbiting Swift observatory. The results will appear in the journal Monthly Notices of the Royal Astronomical Society.

The stars are both helium-rich white dwarfs, the compact remnants that are the end state of stars like our Sun. Reflecting their location in the direction of the constellation of Draco, they are named KL Dra. They are separated by a distance equivalent to just half that between the Earth and Moon, close enough for the more massive partner to drag helium off its lighter companion.

The resulting stream of helium travels from one white dwarf and eventually lands on the other at speeds of millions of km per hour. Most of the time the material gets jammed up in a swirling disc around the accreting companion, with only a trickle landing on the star itself, causing it to quietly glow at optical, ultra-violet and X-ray energies. However, the team discovered that every two months the material in the disc gets suddenly released in a giant eruption that causes the stellar system to shine tens of times more brightly than before.

This binary is one of very few systems on a strict helium diet. The hydrogen which was originally in both stars has long been converted into helium and heavier elements. Almost all other interacting binary systems so far discovered transfer hydrogen material instead. Since helium is heavier and has different properties to hydrogen, the team expect the eruption properties of KL Dra to be different to those of the more familiar hydrogen eating binaries.

As KL Dra is a helium eating binary that erupts regularly and predictably, scientists can plan detailed and sensitive observations using a range of telescopes when it is in outburst. These observations will potentially have wide ranging implications since the same general process of accretion takes place in many astrophysical systems, ranging from young stars in the process of forming, to massive black holes found at the centre of galaxies.

The team of astronomers obtained complementary observations of KL Dra using the Swift observatory. This showed that the eruption was seen very strongly in ultraviolet (UV) light. Surprisingly, unlike the hydrogen eating binaries there was no change in the system's brightness in X-rays during the eruption.

Tom Barclay, a postgraduate student at Armagh Observatory and UCL's Mullard Space Science Laboratory said, "We have a programme to take observations of a dozen helium eating binaries using the Liverpool Telescope to see if they behave in the same way. It was a big surprise to see a second outburst from KL Dra just two months after the first. We then predicted the next outburst would start on December 7th of last year. It was very exciting when our observations showed that it went into outburst on exactly that date!"

Prof. Iain Steele, Director of the Liverpool Telescope commented, "This is another excellent example of the unique power of our robotic telescope that proves particularly effective when it works with space based observatories like Swift. In this case it helped us to discover a completely new type of celestial object. The flexible schedule of the Liverpool Telescope makes it easy for us to coordinate our observations with other facilities and monitor objects that vary on timescales from seconds to years. This approach is virtually impossible with a conventional professional observatory."

Dr Simon Rosen of the University of Leicester and part of the team who made the discovery added, "Thankfully, X-rays and most UV radiation doesn’t get through the Earth's atmosphere, so only space-based observatories can observe the high-energy emission from these extreme objects. With its unrivalled capability for making very frequent X-ray and UV observations, we were able to use the Swift to probe the system at high energies and confirm the Liverpool Telescope result.”

Dr Ramsay is delighted by the team’s work. “Projects like this can take several years to deliver results, so it was great to get such an interesting finding after just a few months.”

Contacts:

Dr Gavin Ramsay

Armagh Observatory

Northern Ireland

Tel: +44 (0)28 3751 2951

Mob: +44 (0)7974 810324

Email: gar@arm.ac.uk

Tom Barclay

Armagh Observatory

Northern Ireland,

Tel: +44 (0)28 2751 2967

Email: tsb@arm.ac.uk

Prof. Iain Steele

Director, Liverpool Telescope

Liverpool John Moores University

Email: ias@astro.livjm.ac.uk

Tel: +44 (0)151 231 2912

Dr Julian Osborne (Swift contact)

University of Leicester

Tel: +44 (0)116 252 3598

Email: julo@star.le.ac.uk

Dr Robert Massey

Royal Astronomical Society

Tel: +44 (0)20 7734 3307 x. 214

Mob: +44 (0)794 124 8035

Email: rm@ras.org.uk

Image and caption:

http://www.arm.ac.uk/~gar/kldra-impression.jpg

An artist’s impression of the helium eating binary KL Dra. The stream of helium can be seen flowing from the lighter star on the right to its more massive companion on the left. Credit: R. Hynes and G. Roelofs.

Notes for editors:

The research has been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society, under the title `Multi-wavelength observations of the helium dwarf nova KL Dra through its outburst cycle'. The authors are: Gavin Ramsay (Armagh Observatory), Iwona Kotko (Jagiellonian Observatory, Poland), Tom Barclay (Armagh and UCL/MSSL), Simon Rosen (University of Leicester), Chris Copperwheat, Tom Marsh, Danny Steeghs, Peter Wheatley (University of Warwick) and Simon Jeffery (Armagh). A pre-print can be seen at http://xxx.soton.ac.uk/abs/1005.3398

Liverpool Telescope:

The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. http://telescope.livjm.ac.uk/

Swift:

Swift is managed by NASA's Goddard Space Flight Center. It was built and is being operated in collaboration with Penn State University, University Park, Pa., the Los Alamos National Laboratory in New Mexico, and General Dynamics of Gilbert, Ariz., in the USA. International collaborators include the University of Leicester and University College London's Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy, and additional partners in Germany and Japan. http://www.swift.ac.uk/

Additional Facilities:

The research paper also presents data obtained using the William Herschel Telescope; the Isaac Newton Telescope on La Palma (both part of the Isaac Newton Group of Telescope's) and the Gemini Telescope North (located on Hawaii). All these facilities receive financial support from the UK Science and Technology Facilities Council.

Armagh Observatory receives core funding from the Northern Ireland Government via the Department of Culture, Arts and Leisure.

The Royal Astronomical Society

The Royal Astronomical Society (RAS: www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.