Wednesday, February 29, 2012

Young Stars Flicker Amidst Clouds of Gas and Dust

This new view of the Orion nebula highlights fledging stars hidden in the gas and clouds. Image credit: NASA/ESA/JPL-Caltech/IRAM. Full image and caption

PASADENA, Calif. - Astronomers have spotted young stars in the Orion nebula changing right before their eyes, thanks to the European Space Agency's Herschel Space Observatory and NASA's Spitzer Space Telescope. The colorful specks -- developing stars strung across the image -- are rapidly heating up and cooling down, speaking to the turbulent, rough-and-tumble process of reaching full stellar adulthood.

The image can be viewed at:

The rainbow of colors represents different wavelengths of infrared light captured by both Spitzer and Herschel. Spitzer is designed to see shorter infrared wavelengths than Herschel. By combining their observations, astronomers get a more complete picture of star formation. NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the Spitzer mission for NASA, and also plays an important role in the European Space Agency-led Herschel mission.

In the portion of the Orion nebula pictured, the telescopes' infrared vision reveals a host of embryonic stars hidden in gas and dust clouds. These stars are at the very earliest stages of evolution.

A star forms as a clump of this gas and dust collapses, creating a warm glob of material fed by an encircling disk. In several hundred thousand years, some of the forming stars will accrete enough material to trigger nuclear fusion at their cores, and then blaze into stardom.

Herschel mapped this region of the sky once a week for six weeks in the late winter and spring of 2011. To monitor for activity in protostars, Herschel's Photodetector Array Camera and Spectrometer probed long infrared wavelengths of light that trace cold dust particles, while Spitzer gauged the warmer dust emitting shorter infrared wavelengths. In this data, astronomers noticed that several of the young stars varied in their brightness by more than 20 percent over just a few weeks. As this twinkling comes from cool material emitting infrared light, the material must be far from the hot center of the young star, likely in the outer disk or surrounding gas envelope. At that distance, it should take years or centuries for material to spiral closer in to the growing starlet, rather than mere weeks.

A couple of scenarios under investigation could account for this short span. One possibility is that lumpy filaments of gas funnel from the outer to the central regions of the star, temporarily warming the object as the clumps hit its inner disk. Or, it could be that material occasionally piles up at the inner edge of the disk and casts a shadow on the outer disk.

"Herschel's exquisite sensitivity opens up new possibilities for astronomers to study star formation, and we are very excited to have witnessed short-term variability in Orion protostars," said Nicolas Billot, an astronomer at the Institut de Radioastronomie Millimétrique (IRAM) in Grenada, Spain who is preparing a paper on the findings along with his colleagues. "Follow-up observations with Herschel will help us identify the physical processes responsible for the variability."

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at JPL. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the United States astronomical community. Caltech manages JPL for NASA.

More information is online at , and .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

Tuesday, February 28, 2012

XMM-Newton measures the power of black-hole driven outflows in galaxies

Artist's impression of ultra-fast outflows and relativistic jets driven by a supermassive black hole at the centre of a galaxy. Credit: ESA/AOES Medialab. Hi-Res [jpg] 4,402.79 kb

Astronomers using ESA's XMM-Newton X-ray Observatory have discovered that ultra-fast outflows are quite common in active galaxies. About 40 per cent of the sources in their sample show outflows that arise from the vicinity of the central black holes. By estimating the mass and energy released by the outflows, the astronomers have identified them as major agents in the feedback processes required by models of galactic evolution to explain the observed correlation between the mass of black holes and the stellar content of their host galaxies.

What determines the mass of galaxies and of the supermassive black holes residing at their cores? Is there a universal physical mechanism that regulates the growth of both components? These are among the most hotly debated topics concerning galactic evolution scenarios, and a new study, reporting on the detection of massive outflows streaming away from the centres of galaxies, is shedding new light on these issues.

In recent years, astronomers have noticed a strong correlation between the mass of a black hole and the stellar content of its host galaxy: more massive black holes appear to reside in galaxies whose bulges contain more stars that also move faster, on average. These empirical relations are quite puzzling, given that they connect two extremely different scales – the close environment of the black hole and the entire extent of the galaxy that harbours it. In fact, the enormous gravitational attraction exerted by the black hole is only effective in the vicinity of the black hole and has hardly any impact on the galaxy at large.

To explain these observed relations astronomers often invoke some sort of feedback: a matter remixing mechanism that originates in the accretion disc feeding the black hole and then propagates throughout the entire galaxy. It had been thought that relativistic jets of highly energetic particles, such as those observed streaming from the centres of almost all active galaxies at radio wavelengths, could play this role. However, simulations show that these jets, which are strongly collimated, cannot provide enough feedback and only have a major impact on the outskirts of their host galaxy; neither is the radiative feedback produced by the intense luminosity of the active galactic nucleus (AGN) sufficient to regulate global galactic properties. The results of simulations seem to point to the need for an additional feedback agent besides these two: wide-angle galactic outflows that arise from ionised material in the accretion disc.

Such outflows can be observed by detecting blue-shifts in the absorption lines of the galaxy spectra. These lines arise from highly ionised iron atoms in clouds located in the very centre of a galaxy, in the immediate surroundings of the black hole. In recent years, astronomers have identified such outflows in a few galaxies, but the observations have thus far been too sparse to allow a quantitative analysis of the phenomenon. Now, the first systematic scrutiny of these outflows in a sample of 42 nearby AGN-hosting galaxies has been performed using data from ESA's XMM-Newton X-ray Observatory. The study, led by Francesco Tombesi from NASA's Goddard Space Flight Center in Greenbelt, USA, demonstrates for the first time that these outflows have the 'right' characteristics to produce the feedback effects required to reconcile observations with the predictions from simulations.

"We have seen these outflows in 40 per cent of the galaxies in our sample, thus demonstrating that they are quite a common phenomenon in these sources," comments Tombesi, lead author of the three papers reporting the results. Analysing the spectroscopic data and comparing them to models of the inner regions of AGN, Tombesi and his colleagues estimated the physical parameters of the outflows: velocity, density and ionisation properties. "We call them ultra-fast outflows, or UFOs, because their velocities are very large – between 10 000 and 100 000 kilometres per second. With these mildly-relativistic velocities, UFOs are much faster, hence much more powerful, than other, ordinary galactic outflows, although they are still slower than relativistic jets," he adds.

The analysis shows that these UFOs consist of highly ionised plasma, which locates their origin extremely close to the black hole as the material must have been exposed to the intense radiation emitted by the accretion disc in order to reach such high levels of ionisation. The high column density of the outflowing material, on the other hand, suggests that the quantities of matter released via the UFOs are substantial, up to one solar mass per year.

"We then used the velocity, density and ionisation level of the outflows estimated from the data to assess the strength of their impact on the host galaxies," notes co-author Massimo Cappi from Istituto Nazionale di Astrofisica – Istituto di Astrofisica Spaziale e Fisica Cosmica in Bologna, Italy. The kinetic power of the UFOs appears to be a few per cent of the total luminosity of the AGN, which is enough to exert sufficient feedback on the host galaxy, as simulations suggest. Moreover, by comparing the density and velocity of the outflowing material, the astronomers have determined the mass loss rate caused by the UFOs. "Interestingly, the rate at which mass is released in the outflows is of the same order as the black-hole accretion rate, and might even exceed it in some cases," Cappi adds.

The result demonstrates, for the first time, that a major mass recycling process is taking place between the dense galactic centres and the diffuse interstellar medium of the host galaxies. This synergy between accretion and ejection processes suggests that something does link AGN and galactic processes on much larger scales. "The outflows studied in our work exert a more intense feedback on the host galaxy than do jets. Since they are more massive, slower and have wider opening angles, they are bound to interact more significantly with the interstellar medium," explains Tombesi. These feedback mechanisms may be able to quench star formation in the bulge and the growth of the black hole at the same time, thus contributing to establishing the observed correlations between the properties of these two components.

"Astronomers have been using XMM-Newton to study these outflows since their earliest detections," comments Norbert Schartel, XMM-Newton Project Scientist at ESA. The observatory's unprecedented spectral resolution is instrumental in measuring with great precision the blue-shifted lines caused by outflows. "It is very satisfying to see how the accumulation of such a large sample has provided the body of data needed to establish the role of these outflows in the context of cosmological feedback," he adds.

After having demonstrated that these outflows are common in active galaxies and that they can have a major role in feedback processes, Tombesi and his colleagues plan to investigate them in greater detail by comparing the data with models and simulations of accretion around black holes. "We intend now to focus on figuring out the detailed physical mechanisms that generate the outflows in the first place. This will represent a further, valuable step towards a full understanding of how active galaxies work and evolve," concludes Tombesi.

Notes for editors

The findings presented here are based on the analysis of a sample of 42 nearby radio-quiet active galactic nuclei (AGN) with redshifts up to z=0.1 observed with ESA's XMM-Newton.

The sample of radio-quiet AGN has been drawn from the Rossi X-ray Timing Explorer (RXTE) All-Sky Slew Survey Catalog, which provides a list of 294 sources serendipitously detected in the hard X-rays. The survey is 90% complete to a 4-sigma limiting flux of ~10-11 erg/s/cm² in the 4-10 keV band. From this survey, the team of astronomers have selected all sources identified as Seyfert galaxies and for which good-quality observations with XMM-Newton were available; this resulted in a sample of 42 sources.

The study presents analyses of X-ray spectra of these 42 AGN taken with the EPIC pn instrument on XMM-Newton. In particular, the astronomers searched for absorption lines of highly ionised iron atoms at energies between 7 and 10 keV, as the blue-shift of these lines provides evidence of outflowing material from the vicinity of the galactic nuclei.

Related publications

F. Tombesi, et al., "Evidence for ultra-fast outflows in radio-quiet AGNs. III. Location and energetics", 2012, Monthly Notices of the Royal Astronomical Society, in press

F. Tombesi, et al., "Evidence for ultra-fast outflows in radio-quiet Active Galactic Nuclei. II. Detailed photo-ionization modeling of Fe K-shell absorption lines", 2011, The Astrophysical Journal, 742, 44

F. Tombesi, et al., "Evidence for ultra-fast outflows in radio-quiet AGNs. I. Detection and statistical incidence of Fe K-shell absorption lines", 2010, Astronomy and Astrophysics, 521, A57


Francesco Tombesi
X-ray Astrophysics Laboratory and CRESST
NASA/Goddard Space Flight Center
and Department of Astronomy
University of Maryland, MD, U.S.A.
Phone: +1-301-405-3615

Massimo Cappi
Istituto Nazionale di Astrofisica
Istituto di Astrofisica Spaziale e Fisica Cosmica

Bologna, Italy
Phone: +39-051-639-8689

Norbert Schartel
ESA XMM-Newton Project Scientist
Directorate of Science and Robotic Exploration
European Space Agency
Phone: +34-91-8131-184

Saturday, February 25, 2012

Discovering New Frontiers in Astronomy with TMT/IRMS

Figure 1: The Arches Cluster Images
The Arches cluster images, as seen in increasing resolution from left-to-right: Lick 3m (Figer 1995), Keck (Serabyn et al 1998), HST (Figer et al 1999), VLT (Stolte et al 2005) and Keck/LGSAO (Kim et al 2006), (Figure provided by D. Figer, private communication).

Figure 2: Metallicity-SFR relation in stellar mass bins
The small points (open boxes) are low-z galaxies from the SDSS. Lines are the fits to these data. The filled circles are high-z galaxies in the same mass bin, with their red-shifts labeled (the figure is from Mannucci et al 2010).

Figure 3: Galaxy Image and Simulations
Left: real WFC2 image showing mergers of U6471 and U6472 at z=0.01. Middle: simulated image showing how this system would look like with JWST at 1.76 micron at z=5.0. Right: simulated JWST image of the galaxy at 3.81 micron at z=12.0

With the commissioning of the Thirty Meter Telescope (TMT) later this decade, a new era in observational astronomy will begin.

Among the first-light instruments planned for the TMT, is the Infra-Red Multi-object Spectrograph (IRMS), which would enable detail study of the nature and properties of the faintest objects in our Universe. The IRMS will be placed behind an Adaptive Optics system on TMT and will provide much sharper images with higher sensitivity over 2 arcmin diameter field-of-view (FoV). The combination of the multiplexing capability of the IRMS, its sensitivity and TMT aperture, provides a unique opportunity to address the most fundamental questions in astronomy.

Understanding properties of massive star clusters is essential in addressing a range of questions from establishing local distance scale and studying star formation activity, to the early Universe where the first generation of stars were formed and contributed to the re-ionization process. They control the dynamical and chemical evolution of their local environment through their effect on the interstellar medium, dominate early evolution of the first galaxies and are likely progenitors of the most energetic processes in the Universe, the Gamma Ray Bursts. The most massive of these objects end their lives as supernovae, producing the heavy elements that build the elements for formation of planets and eventually, life. These star clusters are expected to be in Galactic disks, where detailed observations are difficult due to high extinction and limited spatial and spectral resolution available (Figure 1). The combination of IRMS and TMT will be a powerful tool for discovering new massive star clusters in our Galaxy. With only a few minutes of exposure time, we can easily verify the presence of massive stars down to a mass of ~10 Msun, within 8 kpc from the center of the star clusters. This allows measurement of the stellar content, age, mass and metallicity of a currently unidentified population of massive clusters in the Galaxy.

One outstanding question in observational cosmology is the evolution of star formation, metallicity and stellar mass in galaxies with cosmic time. Star formation in galaxies builds up their stellar mass and enriches their metal content. Therefore, these parameters are inter-related. Figure 2 shows changes in metallicity with star formation for galaxies in different mass intervals, taken from the Sloan Digital Sky Survey (SDSS). A clear trend exists for nearby galaxies in that, galaxies with lower star formation rate (SFR) have higher stellar mass and higher metallicities. The trend appears to continue to z~2, although with larger scatter (Figure 2). However, there is very little overlap between the low- and high-redshift galaxies, with high-redshift objects only sampling the high SFR and high mass end of the distribution. It is not clear how the mass-metallicity relation behaves for low star forming and low mass galaxies at high redshifts (where the bulk of star formation activity is taking place). Furthermore, there are some indications for evolution in the mass-metallicity-SFR relation beyond z~3, but there are only a handful of sources with available data at that redshift. The TMT aperture, combined with the sensitivity, wavelength coverage and multiplexing capability of the IRMS allows, via measurement of the [OII], [OIII], and H-beta line fluxes, a determination of the oxygen abundances in galaxies up to z~3.8. This also enables study of the metallicity-mass-SFR relation for low star-forming/low mass galaxies at high-redshifts.

Over the last decade, a large number of discoveries were made by complementary observations between the Hubble Space Telescope (HST) and ground-based Keck telescopes. Similarly, the combined capabilities of the James Webb Space Telescope (JWST) and the TMT/IRMS could provide exceptional opportunity for discovery. Compared to the JWST, the TMT will provide ~25 times larger light collecting area. Furthermore, the relatively small field of view of the IRMS with adaptive optics, limits the contamination by sky background when long exposures are taken. This makes the TMT/IRMS an ideal instrument for high S/N ratio follow-up spectroscopy of high redshift candidates found by JWST. Many of these sources have Lyman-alpha emission lines. Figure 3 shows the simulated image of a nearby merging system, shifted to z=5 and 12, as expected to be seen at 3.8 microns by JWST. Follow-up high spatial resolution spectroscopy with IRMS of such merging systems allows study of the nature of individual components (i.e. by searching for He 1640 lines), which would grow to form larger and more massive galaxies we observe today. The IRMS will enable measurement of velocity dispersions of UV lines in both absorption and emission, probing gas infall/outflow and winds in multi-component systems at z>4. This will reveal the nature of the first generation of galaxies.

Figer, D. 1995 ApJ. 447, , 29
Figer, D. et al 1999 Ap.J 525, 750
Kim, S. et al 2006 ApJ 653, 113

Mannucci, F. et al 2010 MNRAS
astro-ph 1005.0006
Serabyn, E. et al 1998 Nature 394, 448
Stolte et al 2005 ApJ 628, L113

By Bahram Mobasher
The author would also like to acknowledge helpful discussions with Don Figer and Brian Siana.

Preview of a Forthcoming Supernova

Eta Carinae
Credit: ESA/Hubble & NASA

At the turn of the 19th century, the binary star system Eta Carinae was faint and undistinguished. In the first decades of the century, it became brighter and brighter, until, by April 1843, it was the second brightest star in the sky, outshone only by Sirius (which is almost a thousand times closer to Earth). In the years that followed, it gradually dimmed again and by the 20th century was totally invisible to the naked eye.

The star has continued to vary in brightness ever since, and while it is once again visible to the naked eye on a dark night, it has never again come close to its peak of 1843.

The larger of the two stars in the Eta Carinae system is a huge and unstable star that is nearing the end of its life, and the event that the 19th century astronomers observed was a stellar near-death experience. Scientists call these outbursts supernova impostor events, because they appear similar to supernovae but stop just short of destroying their star.

Although 19th century astronomers did not have telescopes powerful enough to see the 1843 outburst in detail, its effects can be studied today. The huge clouds of matter thrown out a century and a half ago, known as the Homunculus Nebula, have been a regular target for Hubble since its launch in 1990. This image, taken with the Advanced Camera for Surveys High Resolution Channel is the most detailed yet, and shows how the material from the star was not thrown out in a uniform manner, but forms a huge dumbbell shape.

Eta Carinae is not only interesting because of its past, but also because of its future. It is one of the closest stars to Earth that is likely to explode in a supernova in the relatively near future (though in astronomical timescales the “near future” could still be a million years away). When it does, expect an impressive view from Earth, far brighter still than its last outburst: SN 2006gy, the brightest supernova ever observed, came from a star of the same type.

This image consists of ultraviolet and visible light images from the High Resolution Channel of Hubble’s Advanced Camera for Surveys. The field of view is approximately 30 arcseconds across.


Previous images of Eta Carinae from the Hubble Space Telescope:

Source: ESA/Hubble - Space Telescope

Thursday, February 23, 2012

The Many Moods of Titan

This series of false-color images obtained by NASA's Cassini spacecraft shows the dissolving cloud cover over the north pole of Saturn's moon Titan. Image credit: NASA/JPL-Caltech/University of Arizona/CNRS/LPGNantes. Full image and caption

This series of images obtained by NASA's Cassini spacecraft shows several views of the north polar cloud covering Saturn's moon Titan. Image credit: NASA/JPL-Caltech/University of Arizona/CNRS/LPGNantes/SSI. Full image and caption - enlarge image

This artist's concept shows a possible model of Titan's internal structure that incorporates data from NASA's Cassini spacecraft. In this model, Titan is fully differentiated, which means the denser core of the moon has separated from its outer parts. Image credit: A. D. Fortes/UCL/STFC. Full image and caption -Full image with labels - enlarge image

A set of recent papers, many of which draw on data from NASA's Cassini spacecraft, reveal new details in the emerging picture of how Saturn's moon Titan shifts with the seasons and even throughout the day. The papers, published in the journal Planetary and Space Science in a special issue titled "Titan through Time", show how this largest moon of Saturn is a cousin - though a very peculiar cousin - of Earth.

"As a whole, these papers give us some new pieces in the jigsaw puzzle that is Titan," said Conor Nixon, a Cassini team scientist at the NASA Goddard Space Flight Center, Greenbelt, Md., who co-edited the special issue with Ralph Lorenz, a Cassini team scientist based at the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. "They show us in detail how Titan's atmosphere and surface behave like Earth's - with clouds, rainfall, river valleys and lakes. They show us that the seasons change, too, on Titan, although in unexpected ways."

A paper led by Stephane Le Mouelic, a Cassini team associate at the French National Center for Scientific Research (CNRS) at the University of Nantes, highlights the kind of seasonal changes that occur at Titan with a set of the best looks yet at the vast north polar cloud.

A newly published selection of images - made from data collected by Cassini's visual and infrared mapping spectrometer over five years - shows how the cloud thinned out and retreated as winter turned to spring in the northern hemisphere.

Cassini first detected the cloud, which scientists think is composed of ethane, shortly after its arrival in the Saturn system in 2004. The first really good opportunity for the spectrometer to observe the half-lit north pole occurred on December 2006. At that time, the cloud appeared to cover the north pole completely down to about 55 degrees north latitude. But in the 2009 images, the cloud cover had so many gaps it unveiled to Cassini's view the hydrocarbon sea known as Kraken Mare and surrounding lakes.

"Snapshot by snapshot, these images give Cassini scientists concrete evidence that Titan's atmosphere changes with the seasons," said Le Mouelic. "We can't wait to see more of the surface, in particular in the northern land of lakes and seas."

In data gathered by Cassini's composite infrared mapping spectrometer to analyze temperatures on Titan's surface, not only did scientists see seasonal change on Titan, but they also saw day-to-night surface temperature changes for the first time. The paper, led by Valeria Cottini, a Cassini associate based at Goddard, used data collected at a wavelength that penetrated through Titan's thick haze to see the moon's surface. Like Earth, the surface temperature of Titan, which is usually in the chilly mid-90 kelvins (around minus 288 degrees Fahrenheit), was significantly warmer in the late afternoon than around dawn.

"While the temperature difference - 1.5 kelvins - is smaller than what we're used to on Earth, the finding still shows that Titan's surface behaves in ways familiar to us earthlings," Cottini said. "We now see how the long Titan day (about 16 Earth days) reveals itself through the clouds."

A third paper by Dominic Fortes, an outside researcher based at University College London, England, addresses the long-standing mystery of the structure of Titan's interior and its relationship to the strikingly Earth-like range of geologic features seen on the surface. Fortes constructed an array of models of Titan's interior and compared these with newly acquired data from Cassini's radio science experiment.

The work shows the moon's interior is partly or possibly even fully differentiated. This means that the core is denser than outer parts of the moon, although less dense than expected. This may be because the core still contains a large amount of ice or because the rocks have reacted with water to form low-density minerals.

Earth and other terrestrial planets are fully differentiated and have a dense iron core. Fortes' model, however, rules out a metallic core inside Titan and agrees with Cassini magnetometer data that suggests a relatively cool and wet rocky interior. The new model also highlights the difficulty in explaining the presence of important gases in Titan's atmosphere, such as methane and argon-40, since they do not appear to be able to escape from the core.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory manages the mission for NASA's Science Mission Directorate, Washington, D.C. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center in Greenbelt, Md., where the instrument was built. The radio science subsystem has been jointly developed by NASA and the Italian Space Agency.

Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.

Elizabeth Zubritsky 301-614-5438
Goddard Space Flight Center, Greenbelt, Md.

Spectacularly bright object in Andromeda caused by 'normal' black hole

A Hubble Space Telescope optical image of our nearest neighbour galaxy, Andromeda (M31), with the inset an X-ray image of the active centre made with the XMM-Newton observatory. The newly discovered ULX is highlighted. Credit: MPE

An animated gif based on X-ray images from XMM-Newton, showing the ULX from the time it was first seen to enter outburst at the end of 2009 and its decay until it 'switched off' sometime in 2010. Credit: MPE

A spectacularly bright object recently spotted in one of the Milky Way's neighbouring galaxies is the result of a "normal" stellar black hole, astronomers have found.

An international team of scientists, led by Dr Matt Middleton, of Durham University, analysed the Ultraluminous X-ray Source (ULX), which was originally discovered in the Andromeda galaxy by NASA's Chandra x-ray observatory. They publish their results in the journals Monthly Notices of the Royal Astronomical Society and Astronomy and Astrophysics.

Many ULXs are too far away for astronomers to study, but the relatively close proximity of Andromeda to the Milky Way – around 2.5 million light years – gave the team opportunity to study the phenomenon.

The researchers say their study could begin to answer the question about what causes ULXs. Some scientists believe they are caused by relatively small black holes, a few times the mass of our Sun. These black holes rapidly pull in gas and dust which forms an "accretion disc" and heats up causing the material to emit X-rays.

Other scientists say ULXs are caused by material being dragged in by an intermediate-sized black hole formed from the merger of many stellar black holes with a mass perhaps 1,000 times bigger than the Sun.

The Durham-led findings link the ULX spotted in Andromeda to a normal stellar black hole formed after a massive star exploded as a supernova.

Dr Middleton, of Durham University's Department of Physics, said: "ULX sources are still pretty exotic.

"But our work shows that at least some are linked to the normal black holes left behind after the death of massive stars, objects that are found throughout the Universe, and the way that they drag in surrounding material.

"The ULX in Andromeda flared up because of the black hole's voracious appetite for new material."

Using data from Chandra, the XMM-Newton X-ray observatory, the Swift gamma ray observatory and the Hubble Space Telescope the research team were able to watch a sharp decline in the outburst from the ULX that took place over the next few months.

This decline had not been seen in any ULX before, but is common in stellar-mass X-ray binaries in the Milky Way where a normal star is in close orbit around a black hole. Measurement of energy emissions from the ULX also allowed the team to rule out low rates of accretion that would be expected from an intermediate-mass black hole.

They concluded that the Andromeda ULX had the mass of a large star, in this case about 13 times the mass of the Sun.

Dr Middleton said: "We would like to follow up this work by watching another outburst from the Andromeda ULX. The problem is that these are likely to happen only every few decades so we could be in for a long wait before this source erupts again."

The team hope that the ongoing monitoring of Andromeda by orbiting X-ray observatories may find other ULXs in the same galaxy, giving them another chance to test their theory.

Dr Middleton said: "If we do manage to spot another ULX outburst in Andromeda it will be a big help in understanding the extreme behaviour of black holes and the way they pull in matter – something of great importance in shaping the wider universe."

The research work in the UK was funded by the Science and Technology Facilities Council.


Dr Matt Middleton
Department of Physics
Durham University
Tel: +44 (0)191 334 3728


Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 x214
Mob: +44 (0)794 124 8035

Leighton Kitson
Media Relations Officer
Durham University
Tel: +44 (0)191 334 6074/+44 (0)191 334 6075
Email: /

Dr Hannelore Hämmerle
Press officer
Max-Planck Institute for Astrophysics
Garching, Germany
Tel: +49 (0)89 30000 3980


The new work will be published in "The missing link: a low mass X-ray binary in M31 seen as an ultraluminous X-ray source", Middleton, M. J. et al, Monthly Notices of the Royal Astronomical Society, in press.

A preprint can be downloaded from

A copy of the paper is available on request from Durham University Media Relations Office on +44 (0)191 334 6075 or email

German and English language versions of the release are also available from the Max-Planck-Institut für extraterrestrische Physik (MPE, Garching, Germany) and


Durham University

Durham University is a World Top-100 university with a global reputation in research and education across the arts and humanities, sciences and social sciences. It is England's third oldest university and Durham has been a leading centre of scholarship for a thousand years. At the University's heart is a UNESCO World Heritage site which it owns, together with Durham Cathedral. Durham is consistently ranked in the top few universities in the UK and the leading university in the North. Its residential Collegiate system enables the University to recruit some of the most talented and motivated students from around the world to develop transferable skills such as leadership, alongside academic excellence, which place Durham graduates in the World Top-15 for global student employability.*

* 2011 QS World University Rankings

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The Royal Astronomical Society (RAS,, 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.

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Wednesday, February 22, 2012

NASA's Spitzer Finds Solid Buckyballs in Space

NASA's Spitzer Space Telescope has detected the solid form of buckyballs in space for the first time. To form a solid particle, the buckyballs must stack together, as illustrated in this artist's concept showing the very beginnings of the process. Image credit: NASA/JPL-Caltech. Full image and caption

NASA's Spitzer Space Telescope has detected the solid form of buckyballs in space for the first time. To form a solid particle, the buckyballs must stack together like oranges in a crate, as shown in this illustration. Image credit: NASA/JPL-Caltech. Larger image

PASADENA, Calif. -- Astronomers using data from NASA's Spitzer Space Telescope have, for the first time, discovered buckyballs in a solid form in space. Prior to this discovery, the microscopic carbon spheres had been found only in gas form in the cosmos.

Formally named buckministerfullerene, buckyballs are named after their resemblance to the late architect Buckminster Fuller's geodesic domes. They are made up of 60 carbon molecules arranged into a hollow sphere, like a soccer ball. Their unusual structure makes them ideal candidates for electrical and chemical applications on Earth, including superconducting materials, medicines, water purification and armor.

In the latest discovery, scientists using Spitzer detected tiny specks of matter, or particles, consisting of stacked buckyballs. They found the particles around a pair of stars called "XX Ophiuchi," 6,500 light-years from Earth, and detected enough to fill the equivalent in volume to 10,000 Mount Everests.

"These buckyballs are stacked together to form a solid, like oranges in a crate," said Nye Evans of Keele University in England, lead author of a paper appearing in the Monthly Notices of the Royal Astronomical Society. "The particles we detected are miniscule, far smaller than the width of a hair, but each one would contain stacks of millions of buckyballs."

Buckyballs were detected definitively in space for the first time by Spitzer in 2010. Spitzer later identified the molecules in a host of different cosmic environments. It even found them in staggering quantities, the equivalent in mass to 15 Earth moons, in a nearby galaxy called the Small Magellanic Cloud.

In all of those cases, the molecules were in the form of gas. The recent discovery of buckyballs particles means that large quantities of these molecules must be present in some stellar environments in order to link up and form solid particles. The research team was able to identify the solid form of buckyballs in the Spitzer data because they emit light in a unique way that differs from the gaseous form.

"This exciting result suggests that buckyballs are even more widespread in space than the earlier Spitzer results showed," said Mike Werner, project scientist for Spitzer at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "They may be an important form of carbon, an essential building block for life, throughout the cosmos."

Buckyballs have been found on Earth in various forms. They form as a gas from burning candles and exist as solids in certain types of rock, such as the mineral shungite found in Russia, and fulgurite, a glassy rock from Colorado that forms when lightning strikes the ground. In a test tube, the solids take on the form of dark, brown "goo."

"The window Spitzer provides into the infrared universe has revealed beautiful structure on a cosmic scale," said Bill Danchi, Spitzer program scientist at NASA Headquarters in Washington. "In yet another surprise discovery from the mission, we're lucky enough to see elegant structure at one of the smallest scales, teaching us about the internal architecture of existence."

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

For information about previous Spitzer discoveries of buckyballs, visit hand .

For more information about Spitzer, visit and .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

Trent J. Perrotto 202-358-0321
NASA Headquarters, Washington

Tuesday, February 21, 2012

IGR J17091-3624: NASA'S Chandra Finds Fastest Wind From Stellar-Mass Black Hole

IGR J17091-3624
Credit Illustration: NASA/CXC/M.Weiss

This artist's impression shows a binary system containing a stellar-mass black hole called IGR J17091-3624, or IGR J17091 for short. The strong gravity of the black hole, on the left, is pulling gas away from a companion star on the right. This gas forms a disk of hot gas around the black hole, and the wind is driven off this disk.

New observations with NASA's Chandra X-ray Observatory have clocked the fastest wind ever seen blowing off a disk around this stellar-mass black hole. Stellar-mass black holes are born when extremely massive stars collapse and typically weigh between five and 10 times the mass of the Sun.

The record-breaking wind is moving about twenty million miles per hour, or about three percent the speed of light. This is nearly ten times faster than had ever been seen from a stellar-mass black hole, and matches some of the fastest winds generated by supermassive black holes, objects millions or billions of times more massive.

Another unanticipated finding is that the wind, which comes from a disk of gas surrounding the black hole, may be carrying away much more material than the black hole is capturing.

The high speed for the wind was estimated from a spectrum made by Chandra in 2011. A spectrum shows how intense the X-rays are at different energies. Ions emit and absorb distinct features in spectra, which allow scientists to monitor them and their behavior. A Chandra spectrum of iron ions made two months earlier showed no evidence of the high-speed wind, meaning the wind likely turns on and off over

Fast Facts for IGR J17091-3624:

Category: Black Holes
Coordinates: (J2000) RA 17h 09m 07.92s | Dec -36° 24' 25.20"
Constellation: Scorpius
Observation Dates: 2 pointings on Aug 1 and Oct 6, 2011
Observation Time: 16 hours 40 min
Obs. IDs: 12405, 12406
Instrument: ACIS
References: King, A. et al, 2012, ApJ, 746, L20; arXiv:1112.3648
Distance Estimate: About 28,000 light years

NASA's Hubble Reveals a New Class of Extrasolar Planet

Artist's View of Extrasolar Planet GJ1214b
GJ1214b, shown in this artist's view, is a super-Earth orbiting a red dwarf star 40 light-years from Earth. New observations from NASA's Hubble Space Telescope show that it is a waterworld enshrouded by a thick, steamy atmosphere. GJ1214b represents a new type of planet, like nothing seen in our solar system or any other planetary system currently known. Credit: NASA, ESA, and D. Aguilar (Harvard-Smithsonian Center for Astrophysics) Release Images

Observations by NASA's Hubble Space Telescope have come up with a new class of planet, a waterworld enshrouded by a thick, steamy atmosphere. It's smaller than Uranus but larger than Earth.

Zachory Berta of the Harvard-Smithsonian Center for Astrophysics (CfA) and colleagues made the observations of the planet GJ1214b.

"GJ1214b is like no planet we know of," Berta said. "A huge fraction of its mass is made up of water."

The ground-based MEarth Project, led by CfA's David Charbonneau, discovered GJ1214b in 2009. This super-Earth is about 2.7 times Earth's diameter and weighs almost seven times as much. It orbits a red-dwarf star every 38 hours at a distance of 1.3 million miles, giving it an estimated temperature of 450 degrees Fahrenheit.

In 2010, CfA scientist Jacob Bean and colleagues reported that they had measured the atmosphere of GJ1214b, finding it likely that it was composed mainly of water. However, their observations could also be explained by the presence of a planet-enshrouding haze in GJ1214b's atmosphere.

Berta and his co-authors used Hubble's Wide Field Camera 3 (WFC3) to study GJ1214b when it crossed in front of its host star. During such a transit, the star's light is filtered through the planet's atmosphere, giving clues to the mix of gases.

"We're using Hubble to measure the infrared color of sunset on this world," Berta explained.

Hazes are more transparent to infrared light than to visible light, so the Hubble observations help tell the difference between a steamy and a hazy atmosphere.

They found the spectrum of GJ1214b to be featureless over a wide range of wavelengths, or colors. The atmospheric model most consistent with the Hubble data is a dense atmosphere of water vapor.

"The Hubble measurements really tip the balance in favor of a steamy atmosphere," Berta said.

Since the planet's mass and size are known, astronomers can calculate the density, of only about 2 grams per cubic centimeter. Water has a density of 1 gram per cubic centimeter, while Earth's average density is 5.5 grams per cubic centimeter. This suggests that GJ1214b has much more water than Earth does, and much less rock.

As a result, the internal structure of GJ1214b would be an extraordinarily different world than our world.

"The high temperatures and high pressures would form exotic materials like 'hot ice' or 'superfluid water,' substances that are completely alien to our everyday experience," Berta said.

Theorists expect that GJ1214b formed farther out from its star, where water ice was plentiful, and migrated inward early in the system's history. In the process, it would have passed through the star's habitable zone, where surface temperatures would be similar to Earth's. How long it lingered there is unknown.

GJ1214b is located in the direction of the constellation Ophiuchus, and just 40 light-years from Earth. Therefore, it's a prime candidate for study by the planned James Webb Space Telescope.

A paper reporting these results has been accepted for publication in The Astrophysical Journal and is available online.


Ray Villard
Space Telescope Science Institute, Baltimore, Md.

David Aguilar / Christine Pulliam
Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.
617-495-7462 / 617-495-7463 /

Zachory Berta
Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.

Sunday, February 19, 2012

Unique Kuiper Belt Binary Has Unscathed Orbit

Figure 1: Gemini Multi-Object Spectrograph (on Gemini North, GMOS-N) observation of the “Plutino” binary system 2007 TY430, which is located nearly 40 astronomical units (AU) from the Sun. (The average distance between the Earth and Sun is 1 AU.) The pair is separated by about 42,000 km, which appears here at maximum separation of only 0.7 arcsecond on the sky.

Figure 2: The smooth line shows the model of the orbit of the 2007 TY430 binary, displayed as the motion of one body around the other. Individual observations are marked with crosses (the Subaru discovery and subsequent Gemini observations) and a circle (from the Hubble Space Telescope).

Small icy bodies are the remnant leftovers from the formation of planets in the Solar System. Ongoing observations made with Gemini of an extremely red pair of such Kuiper Belt objects (KBOs) in an orbiting binary system offer an indirect glimpse into the past. Scott Sheppard (Carnegie Institution of Washington), Darin Ragozzine (Harvard-Smithsonian Center for Astrophysics), and Chad Trujillo (Gemini Observatory) obtained nearly monthly observations of the pair, named 2007 TY430, to yield precise measurements of their orbital motion. Uniquely, compared with other Kuiper Belt binaries, this pair’s current mutual orbit is likely primordial, unchanged since the formation of the system. The primordial orbit reveals the binary’s formation mechanism, and therefore provides hints of past conditions during the formation of the Solar System itself. The research team concludes that this system may have formed in a more complex interaction involving yet another body. The composition of the bodies’ ultra-red material is unknown, but it may be associated with organic material and it depends upon the pair’s formation site.

The members of the pair otherwise have the characteristics similar to ordinary KBOs. They are roughly equally sized (at a radius of about 50 km each), with a total mass of nearly 1018 kg, and their mutual orbits are nearly circular. However, the overall location of the pair is somewhat closer to the Sun than the classical Kuiper Belt boundaries. The system likely moved out of the classical Kuiper Belt and then got stuck in their current location, which is favored because of a resonance with Neptune’s gravitational pull. For every three orbits around the Sun that Neptune makes, 2007 TY430 will complete two. This so-called “3:2 resonance” is the same relationship Pluto has with Neptune, so such objects are also known as “Plutinos.”

A widely separated binary pair like 2007 TY430 is not very stable, and indeed this is the first wide, equal-sized binary found in this resonance with Neptune. Most other similar systems have likely disintegrated. Thus, 2007 TY430 is possibly one of the few remaining examples of the type.

Members of the team previously reported the discovery of this system based on observations from the Subaru Telescope. The new work appearing in the March 2012 Astronomical Journal takes advantage of Gemini’s capabilities, using the Gemini Multi-Object Spectrograph to measure the system precisely, despite the apparent separation of the bodies by only 0.7 arcseconds or less on the sky (Figures 1 and 2). This corresponds to the apparent size of a dime at a distance of 3 miles. Capturing such fine measurements requires excellent image quality, which Gemini delivers.

Thursday, February 16, 2012

A Sheep in Wolf-Rayet’s Clothing

Hen 3-1333
Credit: ESA/Hubble & NASA

It’s well known that the Universe is changeable: even the stars that appear static and predictable every night are subject to change.

This image from the NASA/ESA Hubble Space Telescope shows planetary nebula Hen 3-1333. Planetary nebulae are nothing to do with planets — they actually represent the death throes of mid-sized stars like the Sun. As they puff out their outer layers, large, irregular globes of glowing gas expand around them, which appeared planet-like through the small telescopes that were used by their first discoverers.

The star at the heart of Hen 3-1333 is thought to have a mass of around 60% that of the Sun, but unlike the Sun, its apparent brightness varies substantially over time. Astronomers believe this variability is caused by a disc of dust which lies almost edge-on when viewed from Earth, which periodically obscures the star.

It is a Wolf–Rayet type star — a late stage in the evolution of Sun-sized stars. These are named after (and share many observational characteristics with) Wolf–Rayet stars, which are much larger. Why the similarity? Both Wolf–Rayet and Wolf–Rayet type stars are hot and bright because their helium cores are exposed: the former because of the strong stellar winds characteristic of these stars; the latter because the outer layers of the stars have been puffed away as the star runs low on fuel.

The exposed helium core, rich with heavier elements, means that the surfaces of these stars are far hotter than the Sun, typically 25 000 to 50 000 degrees Celsius (the Sun has a comparatively chilly surface temperature of just 5500 degrees Celsius).

So while they are dramatically smaller in size, the Wolf–Rayet type stars such as the one at the core of Hen 3-1333 effectively mimic the appearance of their much bigger and more energetic namesakes: they are sheep in Wolf–Rayet clothing.

This visible-light image was taken by the high resolution channel of Hubble’s Advanced Camera for Surveys. The field of view is approximately 26 by 26 arcseconds.

 Source: ESA/Hubble - Space Telescope

Wednesday, February 15, 2012

Astronomers Watch Delayed Broadcast of a Powerful Stellar Eruption

Carina Nebula
Credit:NASA,NOAO, and A. Rest (Space Telescope Science Institute, Baltimore, Md.)
Acknowledgment: NOAO,AURA, NSF, and N. Smith (University of Arizona)

Astronomers are watching a delayed broadcast of a spectacular outburst from the unstable, behemoth double-star system Eta Carinae, an event initially seen on Earth nearly 170 years ago.

Dubbed the "Great Eruption," the outburst first caught the attention of sky watchers in 1837 and was observed through 1858. But astronomers didn't have sophisticated science instruments to accurately record the star system's petulant activity.

Luckily for today's astronomers, some of the light from the eruption took an indirect path to Earth and is just arriving now, providing an opportunity to analyze the outburst in detail. The wayward light was heading in a different direction, away from our planet, when it bounced off dust clouds lingering far from the turbulent stars and was rerouted to Earth, an effect called a "light echo." Because of its longer path, the light reached Earth 170 years later than the light that arrived directly.

The observations of Eta Carinae's light echo are providing new insight into the behavior of powerful massive stars on the brink of detonation. The views of the nearby erupting star reveal some unexpected results, which will force astronomers to modify physical models of the outburst.

"When the eruption was seen on Earth 170 years ago, there were no cameras capable of recording the event," explained the study's leader, Armin Rest of the Space Telescope Science Institute in Baltimore, Md. "Everything astronomers have known to date about Eta Carinae's outburst is from eyewitness accounts. Modern observations with science instruments were made years after the eruption actually happened. It's as if nature has left behind a surveillance tape of the event, which we are now just beginning to watch. We can trace it year by year to see how the outburst changed."

The team's paper will appear Feb. 16 in a letter to the journal Nature.

Located 7,500 light-years from Earth, Eta Carinae is one of the largest and brightest star systems in our Milky Way galaxy. Although the chaotic duo is known for its petulant outbursts, the Great Eruption was the biggest ever observed. During the 20-year episode, Eta Carinae shed some 20 solar masses and became the second brightest star in the sky. Some of the outflow formed the system's twin giant lobes. Before the epic event, the stellar pair was 140 times heftier than our Sun.

Because Eta Carinae is relatively nearby, astronomers have used a variety of telescopes, including the Hubble Space Telescope, to document its escapades. The team's study involved a mix of visible-light and spectroscopic observations from ground-based telescopes.

The observations mark the first time astronomers have used spectroscopy to analyze a light echo from a star undergoing powerful recurring eruptions, though they have measured this unique phenomenon around exploding stars called supernovae. Spectroscopy captures a star's "fingerprints," providing details about its behavior, including the temperature and speed of the ejected material.

The delayed broadcast is giving astronomers a unique look at the outburst and turning up some surprises. The turbulent star system does not behave like other stars of its class. Eta Carinae is a member of a stellar class called Luminous Blue Variables, large, extremely bright stars that are prone to periodic outbursts. The temperature of the outflow from Eta Carinae's central region, for example, is about 8,500 degrees Fahrenheit (5,000 Kelvin), which is much cooler than that of other erupting stars. "This star really seems to be an oddball," Rest said. "Now we have to go back to the models and see what has to change to actually produce what we are measuring."

Rest's team first spotted the light echo while comparing visible-light observations he took of the stellar duo in 2010 and 2011 with the U.S. National Optical Astronomy Observatory's Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. He obtained another set of CTIO observations taken in 2003 by astronomer Nathan Smith of the University of Arizona in Tucson, which helped him piece together the whole 20-year outburst.

The images revealed light that seemed to dart through and illuminate a canyon of dust surrounding the doomed star system. "I was jumping up and down when I saw the light echo," said Rest, who has studied light echoes from powerful supernova blasts. "I didn't expect to see Eta Carinae's light echo because the eruption was so much fainter than a supernova explosion. We knew it probably wasn't material moving through space. To see something this close move across space would take decades of observations. We, however, saw the movement over a year's time. That's why we thought it was probably a light echo."

Although the light in the images appears to move over time, it's really an optical illusion. Each flash of light is reaching Earth at a different time, like a person's voice echoing off the walls of a canyon.

The team followed up its study with spectroscopic observations, using the Carnegie Institution of Washington's Magellan and du Pont telescopes at Las Campanas Observatory in Chile. That study helped the astronomers decode the light, revealing the outflow's speed and temperature. The observations showed that ejected material was moving at roughly 445,000 miles an hour (more than 700,000 kilometers an hour), which matches predictions.

Rest's group monitored changes in the intensity of the light echo using the Las Cumbres Observatory Global Telescope Network's Faulkes Telescope South in Siding Spring, Australia. The team then compared those measurements with a plot astronomers in the 1800s made of the light brightening and dimming over the course of the 20-year eruption. The new measurements matched the signature of the 1843 peak in brightness.

The team will continue to follow Eta Carinae because light from the outburst is still streaming to Earth. "We should see brightening again in six months from another increase in light that was seen in 1844," Rest said. "We hope to capture light from the outburst coming from different directions so that we can get a complete picture of the eruption."

Rest's team consists of J.L. Prieto, Carnegie Observatories, Pasadena, Calif.; N.R. Walborn and H.E. Bond, Space Telescope Science Institute, Baltimore, Md.; N. Smith, Steward Observatory, University of Arizona, Tucson; F.B. Bianco and D.A. Howell, Las Cumbres Observatory Global Telescope Network, Goleta, Calif., and University of California, Santa Barbara; R. Chornock, R.J. Foley, and W. Fong, Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.; D.L. Welch and B. Sinnott, McMaster University, Hamilton, Ontario; M.E. Huber, Johns Hopkins University, Baltimore, Md.; R.C. Smith, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, La Serena, Chile; I. Toledo, Atacama Large Millimeter Array (ALMA), Chile; D. Minniti, Pontifica Universidad Catolica, Santiago, Chile; and K. Mandel, Harvard-Smithsonian Center for AstroLinkphysics, Cambridge, Mass., and Imperial College London, U.K.


Donna Weaver
Space Telescope Science Institute, Baltimore, Md.

Armin Rest
Space Telescope Science Institute, Baltimore, Md.

Black Hole Came from a Shredded Galaxy

This spectacular edge-on galaxy, called ESO 243-49, is home to an intermediate-mass black hole that may have been stripped off of a cannibalized dwarf galaxy. The estimated 20,000-solar-mass black hole lies above the galactic plane. This is an unlikely place for such a massive back hole to exist, unless it belonged to a small galaxy that was gravitationally torn apart by ESO 243-49. The circle identifies a unique X-ray source that pinpoints the black hole. The X-rays are believed to be radiation from a hot accretion disk around the black hole. The blue light not only comes from the disk, but also from a cluster of hot young stars that formed around the black hole. The galaxy is 290 million light-years from Earth. Hubble can't resolve the stars individually because the suspected cluster is too far away. Their presence is inferred from the color and brightness of the light coming from the black hole's location. Credit: NASA, ESA, and S. Farrell (Sydney Institute for Astronomy, University of Sydney). High Resolution Image (jpg)-Low Resolution Image (jpg)

Cambridge, MA - Astronomers using NASA's Hubble Space Telescope have found a cluster of young, blue stars encircling the first intermediate-mass black hole ever discovered. The presence of the star cluster suggests that the black hole was once at the core of a now-disintegrated dwarf galaxy. The discovery of the black hole and the star cluster has important implications for understanding the evolution of supermassive black holes and galaxies.

"For the first time, we have evidence on the environment, and thus the origin, of this middle-weight black hole," said Mathieu Servillat, who worked at the Harvard-Smithsonian Center for Astrophysics when this research was conducted.

Astronomers know how massive stars collapse to form stellar-mass black holes (which weigh about 10 times the mass of our sun), but it's not clear how supermassive black holes (like the four million solar-mass monster at the center of the Milky Way) form in the cores of galaxies. One idea is that supermassive black holes may build up through the merger of smaller, intermediate-mass black holes weighing hundreds to thousands of suns.

Lead author Sean Farrell, of the Sydney Institute for Astronomy in Australia, discovered this unusual black hole in 2009 using the European Space Agency's XMM-Newton X-ray space telescope. Known as HLX-1 (Hyper-Luminous X-ray source 1), the black hole weighs in at 20,000 solar masses and lies towards the edge of the galaxy ESO 243-49, which is 290 million light-years from Earth.

Farrell and his team then observed HLX-1 simultaneously with NASA's Swift observatory in X-ray and Hubble in near-infrared, optical, and ultraviolet wavelengths. The intensity and the color of the light shows a cluster of young stars, 250 light-years across, encircling the black hole. Hubble can't resolve the stars individually because the suspected cluster is too far away. The brightness and color are consistent with other clusters of young stars seen in other galaxies.

Farrell's team detected blue light from hot gas in the accretion disk swirling around the black hole. However, they also detected red light produced by much cooler gas, which would most likely come from stars. Computer models suggested the presence of a young, massive cluster of stars encircling the black hole.

"What we can definitely say with our Hubble data is that we require both emission from an accretion disk and emission from a stellar population to explain the colors we see," said Farrell.

Such young clusters of stars are commonly seen in nearby galaxies, but not outside the flattened starry disk, as found with HLX-1. The best explanation is that the HLX-1 black hole was the central black hole in a dwarf galaxy. The larger host galaxy then captured the dwarf. Most of the dwarf's stars were stripped away through the collision between the galaxies. At the same time, new young stars were formed in the encounter. The interaction that compressed the gas around the black hole also triggered star formation.

Farrell and Servillat found that the star cluster must be less than 200 million years old. This means that the bulk of the stars were formed following the dwarf's collision with the larger galaxy. The age of the stars tells how long ago the two galaxies crashed into each other.

The future of the black hole is uncertain at this stage. It depends on its trajectory, which is currently unknown. It's possible the black hole may spiral in to the center of the big galaxy and eventually merge with the supermassive black hole there. Alternately, the black hole could settle into a stable orbit around the galaxy. Either way, it's likely to fade away in X-rays as it depletes its supply of gas.

"This black hole is unique in that it's the only intermediate-mass black hole we've found so far. Its rarity suggests that these black holes are only visible for a short time," said Servillat.

More observations are planned this year to track the history of the interaction between the two galaxies.

The new findings are being published in the February 15 issue of the Astrophysical Journal Letters. The journal paper is available online.

This release is being issued jointly with NASA.

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:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics

APEX Turns its Eye to Dark Clouds in Taurus

PR Image eso1209a
APEX image of a star-forming filament in Taurus

Millimetre-range and visible-light views of a star-forming filament in Taurus

PR Image eso1209c
Diagram showing the position of Barnard 211 and Barnard 213 in Taurus

PR Image eso1209d
Digitized Sky Survey Image of part of the Taurus Molecular Cloud


PR Video eso1209a
APEX Turns its Eye to Dark Clouds in Taurus (zoom)

PR Video eso1209b
APEX Turns its Eye to Dark Clouds in Taurus (pan)

Mouseover comparison of a star-forming filament in Taurus
seen at millimetre-range wavelengths and in visible light

Star formation in “dark markings of the sky”

A new image from the APEX (Atacama Pathfinder Experiment) telescope in Chile shows a sinuous filament of cosmic dust more than ten light-years long. In it, newborn stars are hidden, and dense clouds of gas are on the verge of collapsing to form yet more stars. It is one of the regions of star formation closest to us. The cosmic dust grains are so cold that observations at wavelengths of around one millimetre, such as these made with the LABOCA camera on APEX, are needed to detect their faint glow.

The Taurus Molecular Cloud, in the constellation of Taurus (The Bull), lies about 450 light-years from Earth. This image shows two parts of a long, filamentary structure in this cloud, which are known as Barnard 211 and Barnard 213. Their names come from Edward Emerson Barnard’s photographic atlas of the “dark markings of the sky”, compiled in the early 20th century. In visible light, these regions appear as dark lanes, lacking in stars. Barnard correctly argued that this appearance was due to “obscuring matter in space”.

We know today that these dark markings are actually clouds of interstellar gas and dust grains. The dust grains — tiny particles similar to very fine soot and sand — absorb visible light, blocking our view of the rich star field behind the clouds. The Taurus Molecular Cloud is particularly dark at visible wavelengths, as it lacks the massive stars that illuminate the nebulae in other star-formation regions such as Orion (see for example eso1103). The dust grains themselves also emit a faint heat glow but, as they are extremely cold at around -260 degrees Celsius, their light can only be seen at wavelengths much longer than visible light, around one millimetre (see image eso1209b and the mouseover comparison eso1209ea to see how the millimetre-range view appears bright where the visible-light view appears dark and obscured).

These clouds of gas and dust are not merely an obstacle for astronomers wishing to observe the stars behind them. In fact, they are themselves the birthplaces of new stars. When the clouds collapse under their own gravity, they fragment into clumps. Within these clumps, dense cores may form, in which the hydrogen gas becomes dense and hot enough to start fusion reactions: a new star is born. The birth of the star is therefore surrounded by a cocoon of dense dust, blocking observations at visible wavelengths. This is why observations at longer wavelengths, such as the millimetre range, are essential for understanding the early stages of star formation.

The upper-right part of the filament shown here is Barnard 211, while the lower-left part is Barnard 213. The millimetre-range observations from the LABOCA camera on APEX, which reveal the heat glow of the cosmic dust grains, are shown here in orange tones, and are superimposed on a visible light image of the region, which shows the rich background of stars. The bright star above the filament is φ Tauri, while the one partially visible at the left-hand edge of the image is HD 27482. Both stars are closer to us than the filament, and are not associated with it.

Observations show that Barnard 213 has already fragmented and formed dense cores — as illustrated by the bright knots of glowing dust — and star formation has already happened. However, Barnard 211 is in an earlier stage of its evolution; the collapse and fragmentation is still taking place, and will lead to star formation in the future. This region is therefore an excellent place for astronomers to study how Barnard’s “dark markings of the sky” play a crucial part in the lifecycle of stars.

The observations were made by Alvaro Hacar (Observatorio Astronómico Nacional-IGN, Madrid, Spain) and collaborators. The LABOCA camera operates on the 12-metre APEX telescope, on the plateau of Chajnantor in the Chilean Andes, at an altitude of 5000 metres. APEX is a pathfinder for the next generation submillimetre telescope, the Atacama Large Millimeter/submillimeter Array (ALMA), which is being built and operated on the same plateau.

More information

APEX is a collaboration between the Max-Planck-Institut für Radioastronomie (MPIfR), the Onsala Space Observatory (OSO), and ESO, with operations of the telescope entrusted to ESO.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Information about APEX
Images related to APEX


Alvaro Hacar González
Observatorio Astronómico Nacional (OAN-IGN)
Madrid, Spain
Tel: +34 915270107 ext 326

Mario Tafalla
Observatorio Astronómico Nacional (OAN-IGN)
Madrid, Spain
Tel: +34 915270107 ext 337

Douglas Pierce-Price
ESO ALMA/APEX Public Information Officer
Garching, Germany
Tel: +49 89 3200 6759