Friday, May 29, 2009

Suzaku Snaps First Complete X-ray View of a Galaxy Cluster

This Suzaku image shows X-ray emission from hot gas throughout the galaxy cluster PKS 0745-191. Brighter colors indicate greater X-ray emission. The circle is 11.2 million light-years across and marks the region where cold gas is now entering the cluster. Inset: A Hubble optical image of the cluster's central galaxies is shown at the correct scale. Credit: NASA/ISAS/Suzaku/M. George, et al.

The massive radio galaxy PKS 0745-191, for which the cluster is named, appears at the center of this Hubble Space Telescope image. The picture forms the inset in the Suzaku image above. Credit: NASA/STScI/Fabian, et al.

The joint Japan-U.S. Suzaku mission is providing new insight into how assemblages of thousands of galaxies pull themselves together. For the first time, Suzaku has detected X-ray-emitting gas at a cluster's outskirts, where a billion-year plunge to the center begins.

"These Suzaku observations are exciting because we can finally see how these structures, the largest bound objects in the universe, grow even more massive," said Matt George, the study's lead author at the University of California, Berkeley.

The team trained Suzaku's X-ray telescopes on the cluster PKS 0745-191, which lies 1.3 billion light-years away in the southern constellation Puppis. Between May 11 and 14, 2007, Suzaku Justificaracquired five images of the million-degree gas that permeates the cluster.

By looking at a cluster in X-rays, astronomers can measure the temperature and density of the gas, which provides clues about the gas pressure and total mass of the cluster. Astronomers expect that the gas in the inner part of a galaxy cluster has settled into a "relaxed" state in equilibrium with the cluster's gravity. This means that the hottest, densest gas lies near the cluster's center, and temperatures and densities steadily decline at greater distances.

In the cluster's outer regions, though, the gas is no longer in an orderly state because matter is still falling inward. "Clusters are the most massive, relaxed objects in the universe, and they are continuing to form now," said team member Andy Fabian at the Cambridge Institute of Astronomy in the UK. The distance where order turns to chaos is referred to as the cluster's "virial radius."

For the first time, this study shows the X-ray emission and gas density and temperature out to -- and even beyond -- the virial radius, where the cluster continues to form. "It gives us the first complete X-ray view of a cluster of galaxies," Fabian said.

In PKS 0745-191, the gas temperature peaks at 164 million degrees Fahrenheit (91 million C) about 1.1 million light-years from the cluster's center. Then, the temperature declines smoothly with distance, dropping to 45 million F (25 million C) more than 5.6 million light-years from the center. The findings appear in the May 11 issue of Monthly Notices of the Royal Astronomical Society.

To discern the cluster's outermost X-ray emission requires detectors with exceptionally low background noise. Suzaku's advanced X-ray detectors, coupled with a low-altitude orbit, give the observatory much lower background noise than other X-ray satellites. The low orbit means that Suzaku is largely protected by Earth's magnetic field, which deflects energetic particles from the sun and beyond.

"With more Suzaku observations in the outskirts of other galaxy clusters, we'll get a better picture of how these massive structures evolve," added George.

Suzaku ("red bird of the south") was launched on July 10, 2005. The observatory was developed at the Japanese Institute of Space and Astronautical Science (ISAS), which is part of the Japan Aerospace Exploration Agency (JAXA), in collaboration with NASA and other Japanese and U.S. institutions.

Francis Reddy
NASA's Goddard Space Flight Center

Thursday, May 28, 2009

HDF 130 - Ghost Remains After Black Hole Eruption

Credit: X-ray (NASA/CXC/IoA/A.Fabian et al.);
Optical (SDSS), Radio (STFC/JBO/MERLIN)

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This is a composite image showing a small region of the Chandra Deep Field North. Shown in blue is a deep image from the Chandra X-ray Observatory and in red is an image from the Multi-Element Radio Linked Interferometer Network (MERLIN) an array of radio telescopes based in Great Britain. An optical image from the Sloan Digital Sky Survey (SDSS) is shown in white, yellow and orange.

The diffuse blue object near the center of the image is believed to be a cosmic "ghost" generated by a huge eruption from a v in a distant galaxy. This X-ray ghost, a.k.a. HDF 130, remains after powerful radio waves from particles traveling away from the black hole at almost the speed of light, have died off. As the electrons radiate away their energy they produce X-rays by interacting with the pervasive sea of photons remaining from the Big Bang - the cosmic background radiation. Collisions between these electrons and the background photons can impart enough energy to the photons to boost them into the X-ray energy band. The cigar-like shape of HDF 130 and its length of about 2.2 million light years are consistent with the properties of radio jets.

HDF 130 is over 10 billion light years away and existed at a time 3 billion years after the Big Bang, when galaxies and black holes were forming at a high rate. Near the center of the X-ray ghost is a radio point source indicating the presence of a growing supermassive black hole. This source corresponds to the location of a massive elliptical galaxy visible in very deep optical images (not shown here). The nearby red object in the SDSS image located immediately above and to the right of the radio source is another, unrelated galaxy located closer to the Earth.

Fast Facts for HDF 130:

Scale: Image is 8.2 arcmin across
Category: Cosmology/Deep Fields/X-ray Background, Groups & Clusters of Galaxies
Coordinates: (J2000) RA 12h 36m 17.6s | Dec +62° 15' 44.5"
Constellation: Ursa Major
Observation Date: 11/20/2000-02/22/2002
Observation Time: 514
Obs. ID: 167, 238, 234, 957, 2232-2234, 2421, 2423, 3294, 3388-3391, 3408-3409
Color Code: X-ray (Blue); Optical (White, Yellow, Orange); Radio (Red)
Instrument: ACIS
References: Fabian et al. 2009, MNRAS, 395, L67
Distance Estimate: About 10 billion light years

Media contacts:

Janet Anderson
NASA Marshall Space Flight Center, Ala.

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.

More information, including images and other multimedia, can be found at: and

Press Release:

Planet-Hunting Method Succeeds at Last

This artist's concept shows the smallest star known to host a planet. The planet, called VB 10b, was discovered using astrometry, a method in which the wobble induced by a planet on its star is measured precisely on the sky.

The dim, red star, called VB 10, is a so-called M-dwarf, located 20 light-years away in the constellation Aquila. It has only one-twelfth the mass, and one-tenth the size, of our sun. The planet is a gas giant similar in size to Jupiter but with six times the mass. Though the planet is less massive than its star, the two orbs would have a similar diameter.

VB 10b orbits its star about every 9 months at a distance of 50 million kilometers (30 million miles). Image credit: NASA/JPL-Caltech

This artist's diagram compares our solar system (below) to the VB 10 star system. Astronomers successfully used the astrometry planet-hunting method for the first time to discover a gas planet, called VB 10b, around a very tiny star, VB 10. All of the bodies in this diagram are shown in circular insets at the same relative scales.

The VB 10 star is one of the smallest known -- and holds the record for the smallest known to host a planet. It's a dim, red M-dwarf with only one-tenth the size, and one-twelfth the mass, of our sun. Its planet, on the other hand, is quite hefty, with six times the mass of Jupiter. Though the planet is less massive than the star, the two orbs would be about the same size.

The VB 10 system is essentially a shrunken version of our solar system. Even though its planet is at a similar distance from its star as Mercury is from our sun, it wouldn't receive as much heat and would be classified as a "cold Jupiter" similar to our own. If any rocky planets do orbit in the VB 10 system, they would be located even closer in than VB 10b, and could lie within the star's habitable zone -- a region where temperatures are right for water to be liquid.

Astrometry involves measuring the wobble of a star on the sky, caused by an unseen planet yanking it back and forth. Because the VB 10b planet is so big relative to its star, it really tugs the star around. The red circle seen at the center of the VB 10 system shows just how big this wobble is. Because our sun is more massive than VB 10, its planets do not cause it to wobble nearly as much.
Image credit: NASA/JPL-Caltech

This movie shows the star VB 10 moving across the sky over a period of nine years. Image credit: NASA/JPL-Caltech/Palomar

A long-proposed tool for hunting planets has netted its first catch -- a Jupiter-like planet orbiting one of the smallest stars known.

The technique, called astrometry, was first attempted 50 years ago to search for planets outside our solar system, called exoplanets. It involves measuring the precise motions of a star on the sky as an unseen planet tugs the star back and forth. But the method requires very precise measurements over long periods of time, and until now, has failed to turn up any exoplanets.

A team of two astronomers from NASA's Jet Propulsion Laboratory, Pasadena, Calif., has, for the past 12 years, been mounting an astrometry instrument to a telescope at the Palomar Observatory near San Diego. After careful, intermittent observations of 30 stars, the team has identified a new exoplanet around one of them -- the first ever to be discovered around a star using astrometry.

"This method is optimal for finding solar-system configurations like ours that might harbor other Earths," said astronomer Steven Pravdo of JPL, lead author of a study about the results to be published in the Astrophysical Journal. "We found a Jupiter-like planet at around the same relative place as our Jupiter, only around a much smaller star. It's possible this star also has inner rocky planets. And since more than seven out of 10 stars are small like this one, this could mean planets are more common than we thought."

The finding confirms that astrometry could be a powerful planet-hunting technique for both ground- and space-based telescopes. For example, a similar technique would be used by SIM Lite, a NASA concept for a space-based mission that is currently being explored.

The newfound exoplanet, called VB 10b, is about 20 light-years away in the constellation Aquila. It is a gas giant, with a mass six times that of Jupiter's, and an orbit far enough away from its star to be labeled a "cold Jupiter" similar to our own. In reality, the planet's own internal heat would give it an Earth-like temperature.

The planet's star, called VB 10, is tiny. It is what's known as an M-dwarf and is only one-twelfth the mass of our sun, just barely big enough to fuse atoms at its core and shine with starlight. For years, VB 10 was the smallest star known -- now it has a new title: the smallest star known to host a planet. In fact, though the star is more massive than the newfound planet, the two bodies would have a similar girth.

Because the star is so small, its planetary system would be a miniature, scaled-down version of our own. For example, VB 10b, though considered a cold Jupiter, is located about as far from its star as Mercury is from the sun. Any rocky Earth-size planets that might happen to be in the neighborhood would lie even closer in.

"Some other exoplanets around larger M-dwarf stars are also similar to our Jupiter, making the stars fertile ground for future Earth searches," said Stuart Shaklan, Pravdo's co-author and the SIM Lite instrument scientist at JPL. "Astrometry is best suited to find cold Jupiters around all kinds of stars, and thus to find more planetary systems arranged like our home."

Two to six times a year, for the past 12 years, Pravdo and Shaklan have bolted their Stellar Planet Survey instrument onto Palomar's five-meter Hale telescope to search for planets. The instrument, which has a 16-megapixel charge-coupled device, or CCD, can detect very minute changes in the positions of stars. The VB 10b planet, for instance, causes its star to wobble a small fraction of a degree. Detecting this wobble is equivalent to measuring the width of a human hair from about three kilometers away.

Other ground-based planet-hunting techniques in wide use include radial velocity and the transit method. Like astrometry, radial velocity detects the wobble of a star, but it measures Doppler shifts in the star's light caused by motion toward and away from us. The transit method looks for dips in a star's brightness as orbiting planets pass by and block the light. NASA's space-based Kepler mission, which began searching for planets on May 12, will use the transit method to look for Earth-like worlds around stars similar to the sun.

"This is an exciting discovery because it shows that planets can be found around extremely light-weight stars," said Wesley Traub, the chief scientist for NASA's Exoplanet Exploration Program at JPL. "This is a hint that nature likes to form planets, even around stars very different from the sun."

JPL is a partner with the California Institute of Technology in Pasadena in the Palomar Observatory. Caltech manages JPL for NASA. More information about exoplanets and NASA's planet-finding program is at . More information about the Palomar Observatory is at

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

J.D. Harrington 202-358-5241
NASA Headquarters, Washington

Wednesday, May 27, 2009

XMM-Newton takes astronomers to a black hole’s edge

Illustration of a supermassive black hole at the centre of a galaxy. Using new data from ESA’s XMM-Newton spaceborne observatory, astronomers have probed closer than ever to a supermassive black hole lying deep at the core of a distant active galaxy. The black hole at the centre of the galaxy – known as 1H0707-495 – was thought to be partially obscured from view by intervening clouds of gas and dust, but the current observations have revealed the innermost depths of the galaxy. Credits: ESA (Image by C. Carreau)

Using new data from ESA’s XMM-Newton spaceborne observatory, astronomers have probed closer than ever to a supermassive black hole lying deep at the core of a distant active galaxy.

The galaxy – known as 1H0707-495 – was observed during four 48-hr-long orbits of XMM-Newton around Earth, starting in January 2008. The black hole at its centre was thought to be partially obscured from view by intervening clouds of gas and dust, but these current observations have revealed the innermost depths of the galaxy.

“We can now start to map out the region immediately around the black hole,” says Andrew Fabian, at the University of Cambridge, who headed the observations and analysis.

X-rays are produced as matter swirls into a supermassive black hole. The X-rays illuminate and are reflected from the matter before its eventual accretion. Iron atoms in the flow imprint characteristic iron lines on the reflected light. The iron lines are distorted in a number of characteristic ways: they are affected by the speed of the orbiting iron atoms, the energy required for the X-rays to escape the black hole’s gravitational field, and the spin of the black hole. All these features show that the astronomers are tracking matter to within twice the radius of the black hole itself.

XMM-Newton detected two bright features of iron emission in the reflected X-rays that had never been seen together in an active galaxy. These bright features are known as the iron L and K lines, and they can be so bright only if there is a high abundance of iron. Seeing both in this galaxy suggests that the core is much richer in iron than the rest of the galaxy.

The direct X-ray emission varies in brightness with time. During the observation, the iron L line was bright enough for its variations to be followed.

A painstaking statistical analysis of the data revealed a time lag of 30 seconds between changes in the X-ray light observed directly, and those seen in its reflection from the disc. This delay in the echo enabled the size of the reflecting region to be measured, which leads to an estimate of the mass of the black hole at about 3 to 5 million solar masses.

The observations of the iron lines also reveal that the black hole is spinning very rapidly and eating matter so quickly that it verges on the theoretical limit of its eating ability, swallowing the equivalent of two Earths per hour.

The team are continuing to track the galaxy using their new technique. There is a lot for them to study. Far from being a steady process, like water slipping down a plughole, a feeding black hole is a messy eater. “Accretion is a very messy process because of the magnetic fields that are involved,” says Fabian.

Their new technique will enable the astronomers to map out the process in all its glorious complexity, taking them to previously unseen regions at the very edges of this and other supermassive black holes.

Notes for editors:

'The detection of Broad Iron K and L line emission in the Narrow-Line Seyfert 1 Galaxy 1H0707-495 using XMM-Newton', by A. Fabian et al. will be published in Nature tomorrow.

An exploding star in an "exploding" galaxy

Discovery of radio supernova SN 2008iz in the nearby starburst galaxy M82

An international team of radio astronomers have discovered the secret explosion of a massive star, a new supernova, in the nearby galaxy M82. Despite being the closest supernovae discovered in the last five years, the explosion is exclusively detectable at radio wavelengths since the dense gas and dust surrounding the exploding star leave it invisible in other wavebands. Without the obscuration, this explosion would have been visible even with amateur telescopes. The results are published in this week's release of Astronomy & Astrophysics Letters.

Figure 1: Zooming into the center of the galaxy M82, one of the nearest starburst galaxies at a distance of only 12 Million light years. The left image, taken with the Hubble Space Telescope (HST), shows the body of the galaxy in blue and hydrogen gas breaking out from the central starburst in red. The VLA image (top left) clearly shows the supernova (SN 2008iz), taken in May 2008. The high-resolution VLBI images (lower right) shows an expanding shell at the scale of a few light days and proves the transient source as the result of a supernova explosion in M82.
Graphics: Milde Science Communication, HST Image: /NASA, ESA, and The Hubble Heritage Team (STScI/AURA); Radio Images: A. Brunthaler, MPIfR. (Click image for higher resolution).

M82 is an irregular galaxy in a nearby galaxy group located 12 million lightyears from Earth. Despite being smaller than the Milky Way, it harbors a vigorous central starburst in the inner few hundred lightyears. In this stellar factory more stars are presently born than in the entire Milky Way. M82 is often called an 'exploding galaxy', because it looks as if being torn apart in optical and infrared images as the result of numerous supernova explosions from massive stars (see Fig. 1, left). Many remnants from previous supernovae are seen on radio images of M82 and a new supernova explosion was long overdue. For a quarter of century astronomers have tried to catch this cosmic catastrophe in the act and have started to wonder why the galaxy has been so silent in recent years.
The new discovery was first made in April 2009 when the MPIfR's Dr. Andreas Brunthaler examined data just taken (on April 8) with the Very Large Array (VLA) of the National Radio Astronomy Observatory, an interferometer of 27 identical 25 meter telescopes in New Mexico, USA. "I then looked back into older data we had from March and May last year, and there it was as well, outshining the entire galaxy!", he says (see Fig 1, top). Observations taken before 2008 showed neither pronounced radio nor X-ray emission at the position of this supernova.

On the other hand, observations of M82 taken last year with optical telescopes to search for new supernovae showed no signs of this explosion. Furthermore, the supernova is hidden on ultraviolet and X-ray images. The supernova exploded close to the center of the galaxy in a very dense interstellar environment. This could also reveal the mystery about the long silence of M82: many of these events may actually be something like "underground explosions", where the bright flash of light is covered under huge clouds of gas and dust and only radio waves can penetrate this dense material. "This cosmic catastrophe shows that using our radio telescopes we have a front-row seat to observe the otherwise hidden universe", Prof. Heino Falcke from Radboud University/Nijmegen & ASTRON explains. If not obscured, the explosion could have been visible even in a medium-sized amateur telescope.

Radio emission can be detected only from core collapse supernovae, where the core of a massive star collapses and produces a black hole or a neutron star. It is produced when the shock wave of the explosion propagates into dense material surrounding the star, usually material that was shed from the massive progenitor star before it exploded.

By combining data from the ten telescopes of the Very Long Baseline Array (VLBA), the VLA, the Green Bank Telescope in the USA, and the Effelsberg 100m telescope in Germany, using the technique of Very Long Baseline Interferometry (VLBI), the team was able to produce images that show a ring-like structure expanding at more than 40 million km/h or 4% of the speed of light, typical for supernovae. "By extrapolating this expansion back in time, we can estimate the explosion date. Our current data indicate that the star exploded in late January or early February 2008.", explains Dr. Andreas Brunthaler.

Only three months after the explosion, the ring was already 650 times larger than Earth's orbit around the Sun. It takes the extremely sharp view of VLBI observations to resolve this structure which is as large as a 1 Euro coin seen from a distance of 13.000 km.

The asymmetric appearance of the supernova on the VLBI images indicates also that either the explosion was highly asymmetric or the surrounding material unevenly distributed. "Using the super sharp vision of VLBI we can follow the supernova expanding into the dense interstellar medium of M82 over the coming years and gain more insight on it and the explosion itself.", says Prof. Karl Menten, director at the MPIfR.

Discoveries like this supernova will be routine with the next generation of radio telescopes, such as the Low Frequency Array (LOFAR) which is currently under construction in Europe, the Allen Telescope Array (ATA) in the USA, or the planned Square Kilometer Array (SKA). These will have the capability to observe large parts of the sky continously.

Team members were Andreas Brunthaler, Karl M. Menten, Christian Henkel from the MPIfR, Mark J. Reid from the CfA, Geoffrey C. Bower from Berkeley, and Heino Falcke from the University of Nijmegen/ASTRON.

Figure 2: The Very Large Array (left) in New Mexico/USA was used for the initial discovery of the new supernova 2008iz in the galaxy M82. This telescope, together with the Effelsberg 100m telescope (center) and the Green Bank Telescope (right) in West Virginia/USA, complemented the high-resolution VLBA array for the observations of the expanding shell of the supernova.
Images: NRAO, MPIfR Bonn (Click for higher resolution).

Original Publication:

Discovery of a bright radio transient in M82: a new radio supernova?, A. Brunthaler, K.M. Menten, M.J. Reid, C. Henkel, G.C. Bower, H. Falcke, Astronomy & Astrophysics, 2009, Vol. 499, L17 (May 28 issue).

Further Information:

Additional Images

Harvard-Smithsonian Center for Astrophysics (CfA)

Berkeley Astronomy Department University of California

Astrophysics Department
, Radboud University Nijmegen & ASTRON

Very Large Array (VLA)

Very Long Baseline Array (VLBA)

Effelsberg 100m telescope

Green Bank Telescope (GBT, Robert C. Byrd Telescope)


Dr. Andreas Brunthaler,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-377

Prof. Dr. Karl Menten,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-297

Dr. Norbert Junkes,
Public Outreach,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-399

Monday, May 25, 2009

Most Efficient Spectrograph to Shoot the Southern Skies

ESO PR Photo 20a/09
An X-shooter spectrum

ESO PR Photo 20b/09
The X-shooter instrument

ESO PR Photo 20c/09
First Light of X-shooter

ESO’s Very Large Telescope — Europe’s flagship facility for ground-based astronomy — has been equipped with the first of its second generation instruments: X-shooter. It can record the entire spectrum of a celestial object in one shot — from the ultraviolet to the near-infrared — with high sensitivity. This unique new instrument will be particularly useful for the study of distant exploding objects called gamma-ray bursts.

“X-shooter offers a capability that is unique among astronomical instruments installed at large telescopes,” says Sandro D’Odorico, who coordinated the Europe-wide consortium of scientists and engineers that built this remarkable instrument. “Until now, different instruments at different telescopes and multiple observations were needed to cover this kind of wavelength range, making it very difficult to compare data, which, even though from the same object, could have been taken at different times and under different sky conditions.”

X-shooter collects the full spectrum from the ultraviolet (300 nm) to the near-infrared (2400 nm) in parallel, capturing up to half of all the light from an object that passes through the atmosphere and the various elements of the telescope. “All in all, X-shooter can save us a factor of three or more in terms of precious telescope time and opens a new window of opportunity for the study of many, still poorly understood, celestial sources,” says D’Odorico.

The name of the 2.5-ton instrument was chosen to stress its capacity to capture data highly efficiently from a source whose nature and energy distribution are not known in advance of the observation. This property is particularly crucial in the study of gamma-ray bursts, the most energetic explosions known to occur in the Universe (ESO 17/09). Until now, a rough estimate of the distance of the target was needed, so as to know which instrument to use for a detailed study. Thanks to X-shooter, astronomers won’t have to go through this first observing step. This is particularly relevant for gamma-ray bursts, which fade away very quickly and where being fast is the key to understanding the nature of these elusive cosmic sources.

“I am very confident that X-shooter will discover the most distant gamma-ray bursts in the Universe, or in other words, the first objects that formed in the young Universe,” says François Hammer, who leads the French efforts in X-shooter.

X-shooter was built by a consortium of 11 institutes in Denmark, France, Italy and the Netherlands, together with ESO. In total 68 person-years of work by engineers, technicians and astronomers and a global budget of six million Euros were required. The development time was remarkably fast for a project of this complexity, which was completed in just over five years, starting from the kick-off meeting held in December 2003.

“The success of X-shooter and its relatively short completion time are a tribute to the quality and dedication of the many people involved in the project,” says Alan Moorwood, ESO Director of Programmes.

The instrument was installed at the telescope at the end of 2008 and the first observations in its full configuration were made on 14 March 2009, demonstrating that the instrument works efficiently over the full spectral range with unprecedented resolution and quality. X-shooter has already proved its full capability by obtaining the complete spectra of low metallicity stars, of X-ray binaries, of distant quasars and galaxies, of the nebulae associated with Eta Carinae and the supernova 1987A, as well as with the observation of a distant gamma-ray burst that coincidently exploded at the time of the commissioning run.

X-shooter will be offered to the astronomical community from 1 October 2009. The instrument is clearly answering a need in the scientific community as about 150 proposals were received for the first runs of X-shooter, for a total of 350 observing nights, making it the second most requested instrument at the Very Large Telescope in this period.

More information

ESO’s Very Large Telescope (VLT) is the world’s most advanced optical instrument. It is an ensemble of four 8.2-metre telescopes located at the Paranal Observatory on an isolated mountain peak in the Atacama Desert in North Chile. The four 8.2-metre telescopes have a total of 12 focal stations where different instruments for imaging and spectroscopic observations are installed and a special station where the light of the four telescopes is combined for interferometric observations.

The first VLT instrument was installed in 1998 and has been followed by 12 more in the last 10 years, distributed at the different focal stations. X-shooter is the first of the second generation of VLT instruments and replaces the workhorse-instrument FORS1, which has been successfully used for more than ten years by hundreds of astronomers. X-shooter operates at the Cassegrain focus of the Kueyen telescope (UT2).

In response to an ESO Call for Proposals for second generation VLT instrumentation, ESO received three proposals for an intermediate resolution, high efficiency spectrograph. These were eventually merged into a single proposal around the present concept of X-shooter, which was approved for construction in November 2003. The Final Design Review, at which the instrument design is finalised and declared ready for construction, took place in April 2006. The first observations with the instrument at the telescope in its full configuration were on 14 March 2009.

X-shooter is a joint project by Denmark, France, Italy, the Netherlands and ESO. The collaborating institutes in Denmark are the Niels Bohr and the DARK Institutes of the University of Copenhagen and the National Space Institute (Technical University of Denmark); in France GEPI at the Observatoire de Paris and APC at the Université D. Diderot, with contributions from the CEA and the CNRS; in Italy the Osservatorio di Brera, Trieste, Palermo and Catania; and in the Netherlands, the University of Amsterdam, the University of Nijmegen and ASTRON. Beside the participating institutes and ESO, the project was supported by the National Agencies of Italy (INAF), the Italian Ministry for Education, University and Research (MIUR), the Netherlands (NOVA and NWO) and by the Carlsberg Foundation in Denmark. The project was also supported in Denmark and the Netherlands with funds from the EU Descartes prize, the highest European prize for science, awarded in 2002 to the European collaboration on gamma-ray burst research headed by Professor Ed van den Heuvel.

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe. It is supported by 14 countries: Austria, Belgium, 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 the Atacama Desert region of Chile: La Silla, Paranal and Chajnantor.

Sandro D’Odorico
Phone: +49 89 32 00 62 39

François Hammer
Paris Observatory
Phone: +33 1 45 07 74 08

Per Kjærgaard Rasmussen
Niels Bohr Institute, Copenhagen University, Denmark
Phone: +45 353 259 87

Sofia Randich
INAF-Osservatorio di Arcetri
Phone: +39 055 27 52 251

Lex Kaper
Astronomical Institute "Anton Pannekoek"
Amsterdam, The Netherlands
Phone: +31 20 52 57 474

ESO La Silla - Paranal - ELT Press Officer: Dr. Henri Boffin - +49 89 3200 6222 -
ESO Press Officer in Chile: Valeria Foncea - +56 2 463 3123 -

National contacts for the media:

Thursday, May 21, 2009

Missing Link" Revealing Fast-Spinning Pulsar Mysteries

Astronomers have discovered a unique double-star system that representsa "missing link" stage in what they believe is the birth process of the most rapidly-spinning stars in the Universe -- millisecond pulsars.

"We've thought for some time that we knew how these pulsars get 'spun up' to rotate so swiftly, and this system looks like it's showing us the process in action," said Anne Archibald, of McGill University in Montreal, Canada.

Neutron star with accretion disk (left)
drawing material from companion star (right).
Animations of this system and its evolution.

Pulsars are superdense neutron stars, the remnants left after massive stars have exploded as supernovae. Their powerful magnetic fields generate lighthouse-like beams of light and radio waves that sweep around as the star rotates. Most rotate a few to tens of times a second, slowing down over thousands of years.

However, some, dubbed millisecond pulsars, rotate hundreds of times a second. Astronomers believe the fast rotation is caused by a companion star dumping material onto the neutron star and spinning it up. The material from the companion would form a flat, spinning disk around the neutron star, and during this period, the radio waves characteristic of a pulsar would not be seen coming from the system. As the amount of matter falling onto the neutron star decreased and stopped, the radio waves could emerge, and the object would be recognized as a pulsar.

This sequence of events is apparently what happened with a binary-star system some 4000 light-years from Earth. The millisecond pulsar in this system, called J1023, was discovered by the National Science Foundation's (NSF) Robert C. Byrd Green Bank Telescope (GBT) in West Virginia in 2007 in a survey led by astronomers at West Virginia University and the National Radio Astronomy Observatory (NRAO).

The astronomers then found that the object had been detected by NSF's Very Large Array (VLA) radio telescope during a large sky survey in 1998, and had been observed in visible light by the Sloan Digital Sky Survey in 1999, revealing a Sun-like star.

When observed again in 2000, the object had changed dramatically, showing evidence for a rotating disk of material, called an accretion disk, surrounding the neutron star. By May of 2002, the evidence for this disk had disappeared.

"This strange behavior puzzled astronomers, and there were several different theories for what the object could be," said Ingrid Stairs of the University of British Columbia, who has been visiting the Australia Telescope National Facility and Swinburne University this year.

The 2007 GBT observations showed that the object is a millisecond pulsar, spinning 592 times per second.

"No other millisecond pulsar has ever shown evidence for an accretion disk," Archibald said. "We know that another type of binary-star system, called a low-mass X-ray binary (LMXB), also contains a fast-spinning neutron star and an accretion disk, but these don't emit radio waves. We've thought that LMXBs probably are in the process of getting spun up, and will later emit radio waves as a pulsar. This object appears to be the 'missing link' connecting the two types of systems," she explained.

"It appears this thing has flipped from looking like an LMXB to looking like a pulsar, as it experienced an episode during which material pulled from the companion star formed an accretion disk around the neutron star. Later, that mass transfer stopped, the disk disappeared, and the pulsar emerged," said Scott Ransom of the NRAO.

The scientists have studied J1023 in detail with the GBT, with the Westerbork radio telescope in the Netherlands, with the Arecibo radio telescope in Puerto Rico, and with the Parkes radio telescope in Australia. Their results indicate that the neutron star's companion has less than half the Sun's mass, and orbits the neutron star once every four hours and 45 minutes.

"This system gives us an unparalled 'cosmic laboratory' for studying how millisecond pulsars evolve," Stairs said. Maura McLaughlin, of West Virginia University, agrees: "Future observations of this system at radio and other wavelengths are sure to hold many surprises."

Archibald, Ransom, Stairs and McLaughlin are members of an international scientific team with representatives from McGill University, the University of British Columbia, the NRAO, West Virginia University, and others. The scientists announced their discovery in the May 21 online issue of the journal Science.

Dave Finley, Public Information Officer
Socorro, NM
(575) 835-7302

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

Wednesday, May 20, 2009

Giant Galaxy Messier 87 finally sized up

Using ESO's Very Large Telescope, astronomers have succeeded in measuring the size of giant galaxy Messier 87 and were surprised to find that its outer parts have been stripped away by still unknown effects. The galaxy also appears to be on a collision course with another giant galaxy in this very dynamic cluster.

ESO PR Photo 19a/09
The Intercluster Light

About this image: This deep image of the Virgo Cluster obtained by Chris Mihos and his colleagues using the Burrell Schmidt telescope shows the diffuse light between the galaxies belonging to the cluster. North is up, east to the left. The dark spots indicate where bright foreground stars were removed from the image.

ESO PR Photo 19b/09
Intergalactic Planetary Nebulae

About this image: Location of the planetary nebulae in the outskirts of the giant galaxy Messier 87 and in the intergalactic space around the centre of the Virgo Cluster of galaxies. By measuring the motions of these objects very precisely, using the highly efficient FLAMES spectrograph on the ESO Very Large Telescope at the Paranal Observatory (Chile), astronomers have probed the edge of Messier 87 for the first time, and found it to be about three times as large as our own Milky Way.

ESO PR Photo 19c/09
The Virgo Cluster

About this image: Image of the Virgo cluster of galaxies taken with the Palomar Observatory 48-inch Schmidt telescope as part of the Digitized Sky Survey 2. The giant elliptical galaxy Messier 87 is seen in the centre, while Messier 84 and 86 are the two bright galaxies forming part of the small group on the centre right of the image. New observations obtained with ESO’s Very Large Telescope have shown that the halo of stars around Messier 87 has been truncated, possibly because of some interaction with Messier 84. The observations also reveal that Messier 87 and 86 are moving towards each other.

The new observations reveal that Messier 87’s halo of stars has been cut short, with a diameter of about a million light-years, significantly smaller than expected, despite being about three times the extent of the halo surrounding our Milky Way [1]. Beyond this zone only few intergalactic stars are seen.

“This is an unexpected result,” says co-author Ortwin Gerhard. “Numerical models predict that the halo around Messier 87 should be several times larger than our observations have revealed. Clearly, something must have cut the halo off early on.”

The team used FLAMES, the super-efficient spectrograph at ESO’s Very Large Telescope at the Paranal Observatory in Chile, to make ultra-precise measurements of a host of planetary nebulae in the outskirts of Messier 87 and in the intergalactic space within the Virgo Cluster of galaxies, to which Messier 87 belongs. FLAMES can simultaneously take spectra many sources, spread over an area of the sky about the size of the Moon.

The new result is quite an achievement. The observed light from a planetary nebula in the Virgo Cluster is as faint as that from a 30-Watt light bulb at a distance of about 6 million kilometres (about 15 times the Earth–Moon distance). Furthermore, planetary nebulae are thinly spread through the cluster, so even FLAMES’s wide field of view could only capture a few tens of nebulae at a time.

“It is a little bit like looking for a needle in a haystack, but in the dark”, says team member Magda Arnaboldi. “The FLAMES spectrograph on the VLT was the best instrument for the job”.

At a distance of approximately 50 million light-years, the Virgo Cluster is the nearest galaxy cluster. It is located in the constellation of Virgo (the Virgin) and is a relatively young and sparse cluster. The cluster contains many hundreds of galaxies, including giant and massive elliptical galaxies, as well as more homely spirals like our own Milky Way.

The astronomers have proposed several explanations for the discovered “cut-off” of Messier 87’s, such as collapse of dark matter nearby in the galaxy cluster. It might also be that another galaxy in the cluster, Messier 84, came much closer to Messier 87 in the past and dramatically perturbed it about a billion years ago. “At this stage, we can’t confirm any of these scenarios,” says Arnaboldi. “We will need observations of many more planetary nebulae around Messier 87”.

One thing the astronomers are sure about, however, is that Messier 87 and its neighbour Messier 86 are falling towards each other. “We may be observing them in the phase just before the first close pass”, says Gerhard. “The Virgo Cluster is still a very dynamic place and many things will continue to shape its galaxies over the next billion years.”

More Information
Planetary nebulae (PNe) are the spectacular final phase in the life of Sun-like stars, when the star ejects its outer layers into the surrounding space. Their name is a relic of an earlier era: early observers, using only small telescopes, thought that some of these nearby objects, such as the “Helix Nebula” resembled the discs of the giant planets in the Solar System. Planetary nebulae have strong emission lines, which make them relatively easy to detect at great distances, and also allow their radial velocities to be measured precisely. So planetary nebulae can be used to investigate the motions of stars in the faint outer regions of distant galaxies where velocity measurements are otherwise not possible. Moreover, planetary nebulae are representative of the stellar population in general. As they are relatively short-lived (a few tens of thousands of years — a mere blip on astronomical timescales), astronomers can estimate that one star in about 8000 million of Sun-like stars is visible as a planetary nebula at any given moment. Thus planetary nebulae can provide a unique handle on the number, types of stars and their motions in faint outer galaxy regions that may harbour a substantial amount of mass. These motions contain the fossil record of the history of galaxy interaction and the formation of the galaxy cluster.

This research is presented in a paper to appear in Astronomy and Astrophysics: “The Edge of the M87 Halo and the Kinematics of the Diffuse Light in the Virgo Cluster Core,” by Michelle Doherty et al.

The team is composed of Michelle Doherty and Magda Arnaboldi (ESO), Payel Das and Ortwin Gerhard (Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany), J. Alfonso L. Aguerri (IAC, Tenerife, Spain), Robin Ciardullo (Pennsylvania State University, USA), John J. Feldmeier (Youngstown State University, USA), Kenneth C. Freeman (Mount Stromlo Observatory, Australia), George H. Jacoby (WIYN Observatory, Tucson, AZ, USA), and Giuseppe Murante (INAF, Osservatorio Astronomico di Pino Torinese, Italy).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe. It is supported by 14 countries: Austria, Belgium, 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 the Atacama Desert region of Chile: La Silla, Paranal and Chajnantor.

[1] Although the standard value for the diameter of the Milky Way is about 100 000 light-years, its stellar halo is thought to extend out almost twice as far.

Science paper: arxiv:0905.1958 (download the PDF file - 1.15 MB)

Magda Arnaboldi
ESO, Garching, Germany
Phone: +49-89-3200-6599

Ortwin Gerhard
MPE, Garching, Germany
Phone: +49-89-30000-3539

ESO La Silla - Paranal - ELT Press Officer: Dr. Henri Boffin - +49 89 3200 6222 -
ESO Press Officer in Chile: Valeria Foncea - +56 2 463 3123 -

National contacts for the media:

Monday, May 18, 2009

MMTO Confirms Ultra-faint Object in Milky Way Halo is Dwarf Galaxy

UA and MMT astronomers are searching for the smallest galaxies in the universe.

How small can a galaxy be?

The MMTO, Mount Hopkins, Ariz.
(Photo: Howard Lester, MMTO)

Astronomers are now finding small-fry galaxies that contain fewer than a million, possibly as few as a thousand, stars.

Until recently, these very faint, dwarf galaxies in the halo of the Milky Way have eluded discovery.

Now astronomers are using advanced techniques and instruments at The University of Arizona/Smithsonian 6.5-meter MMT Observatory at Mount Hopkins, Ariz., to find them.

They reported their latest discovery of such a galaxy, in the constellation Aires, in an online preprint last March. Their research article will be published in Monthly Notices, a publication of the Royal Astronomical Society, this summer.

Ed Olszewski

"These are galaxies that might contain as few as a thousand stars, and those stars are being pulled out into the halo of our Milky Way," said UA astronomer Ed Olszewski. UA astronomy professor Jill Bechtold and MMTO astronomer Tim Pickering are also on the project.

This model shows the halo of the Milky Way created solely from destroyed dwarf galaxies. It mimics the large-scale structure of the Milky Way halo and is qualitatively consistent with modern models of the evolution of structure in the Universe. The Milky Way galactic center is at the very center of the illustration. (Illustration credit: Paul Harding, Case University)

"We're trying to understand whether these unbelievably faint objects are intact or have been mostly pulled apart by the Milky Way," Olszewski said. "We're trying to understand what the halo of the Milky Way really looks like, how many of these objects are in the halo, and whether our census of the population in the halo agrees or conflicts with the cosmological models.

"Knowing how many of these incredibly puny satellite galaxies populate our galactic neighborhood is important if we are to know whether cosmological models used to describe the evolution of the structure of galaxies are correct or way off base," he added.

"The sorts of objects we're finding have so few stars that one might think they're not galaxies at all, except that their internal motions imply that, unlike star clusters, they contain dark matter just like big galaxies do," Olszewski said.

A more accurate census of very faint, local dwarf galaxies is important because it will help scientists determine how much dark matter they might contain, he said. Scientists believe that "dark matter," or matter that is observed only by the effects of gravity but cannot be seen otherwise because it emits no radiation, makes up about 25 percent of the universe. "Normal" matter is thought to make up between 2 percent and 4 percent of the universe, with the remaining bulk being dark energy.

A decade ago, theoretical simulations showed that there must be 10 to 100 times as many objects in the Milky Way halo than observers had seen, Olszewski said. "Now we're coming closer to solving the ‘missing satellites' problem and, simultaneously, understanding how the Milky Way was put together."

Olszewski is a member of the observing team who has been using a wide-field imager called Megacam and a wide-field multi-fiber spectrograph called Hectochelle at the MMTO to confirm the existence of what British collaborators analyzing Sloan Digital Sky Survey data have identified as possible dwarf satellite galaxies.

"Until recently, astronomers could find small satellite galaxies just by looking at a photograph," Olszewski said. "We can image small galaxies that typically have one one-millionth as many stars as the Milky Way has. But the ones we're searching for now are 100 times fainter and won't show up in photographs. They are ridiculously hard to find, because they're so faint and because they're hidden in the foreground stars of the Milky Way itself."

The UA/MMT team collaborates with astronomers at the Institute for Astronomy in Cambridge, England. The British astronomers use a mathematical model of stars with the color and brightness of stars in galaxies they're searching for, moving their model as a kind of template against fields of stars recorded in Sloan Digital Sky Survey maps until they find a pattern match.

The Cambridge astronomers have found about 10 satellite galaxies by this "data mining" technique, Olszewski said, but now they're searching for fainter galaxies, which are harder to find. The Cambridge group works with the UA/MMT to confirm the fainter galaxies are real.

"It's a hard observational follow-up project that couldn't be done without the wonderful instruments built for the MMTO by people at the (Harvard-Smithsonian) Center for Astrophysics," Olszewski said.

Megacam has 36 CCDs that give it power to take deep sky images. Hectochelle has 300 fibers for gathering the spectra, or colors, of stars, which shows how far away stars are.

Observers use star velocity and star chemistry to determine if they have actually found an object in the Milky Way halo rather than in the Milky Way itself.

"Given what we know of the Milky Way halo in the context of all the discoveries so far, the model we made of the Milky Way 10 years ago is still a good one," Olszewski said.

The model can be visualized as a big meatball in a bowl of spaghetti. The meatball is the Milky Way, and spaghetti strands winding away in all different directions represent ripped apart small galaxies.

"We are finding not only little galaxies, we are finding some that are embedded in, or near the bigger, million-star sized galaxies," Olszewski said.

"It's getting to look more and more that that's what the halo of the Milky Way is like, and how the halo is assembled. The halo of a big galaxy largely arises from destruction of littler ones. Over time, the Milky Way will eat not only the little satellite galaxies falling in, but also the Magellanic clouds, " he added. "We're far from done forming the Milky Way."

By Lori Stiles, University Communications
Source: UA News - University of Arizona

Saturday, May 16, 2009

NASA's Spitzer Begins Warm Mission

After more than five-and-a-half years of probing the cool cosmos, NASA's Spitzer Space Telescope has run out of the coolant that kept its infrared instruments chilled. The telescope will warm up slightly, yet two of its infrared detector arrays will still operate successfully. The new, warm mission will continue to unveil the far, cold and dusty universe.

Spitzer entered an inactive state called standby mode at 3:11 p.m. Pacific Time (6:11 p.m. Eastern Time or 22:11 Universal Time), May 15, as result of running out of its liquid helium coolant. Scientists and engineers will spend the next few weeks recalibrating the instrument at the warmer temperature, and preparing it to begin science operations.

Additional information, including the following items, is at:

* A full news release about Spitzer's warm mission and past accomplishments
* A mock interview titled "If Spitzer Could Talk: An Interview with NASA's Coolest Space Mission"
* A video about the Spitzer mission
* An article about the late astronomer Lyman Spitzer, the mission's namesake

Who's Who of the Spitzer mission: NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA's Science Mission Directorate in Washington, D.C. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Lockheed Martin Space Systems in Denver, and Ball Aerospace & Technologies Corp., in Boulder, Colo., support mission and science operations. NASA's Goddard Space Flight Center in Greenbelt, Md., built Spitzer's infrared array camera; the instrument's principal investigator was Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Ball Aerospace & Technologies Corp. built Spitzer's infrared spectrograph; its principal investigator was Jim Houck of Cornell University in Ithaca, N.Y. Ball Aerospace & Technologies Corp. and the University of Arizona in Tucson, built the multiband imaging photometer for Spitzer; its principal investigator was George Rieke of the University of Arizona.

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

Printable version (PDF) of this release

Thursday, May 14, 2009

3C305 - An Intriguing Glowing Galaxy

Credit: X-ray (NASA/CXC/CfA/F.Massaro, et al.);
Optical (NASA/STScI/C.P.O'Dea);
Radio (NSF/VLA/CfA/F.Massaro, et al.)

Blog: An Intriguing Glowing
GalaxyHandout: html | pdf
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Activity from a supermassive black hole is responsible for the intriguing appearance of this galaxy, 3C305, located about 600 million light years away from Earth. The structures in red and light blue are X-ray and optical images from the Chandra X-ray Observatory and Hubble Space Telescope respectively. The optical data is from oxygen emission only, and therefore the full extent of the galaxy is not seen. Radio data are shown in darker blue and are from the National Science Foundation's Very Large Array in New Mexico, as well as the Multi-Element Radio-Linked Interferometer Network in the United Kingdom.

An unexpected feature of this multiwavelength image of 3C305 is that the radio emission -- produced by a jet from the central black hole -- does not closely overlap with the X-ray data. The X-ray emission does, however, seem to be associated with the optical emission.

Using this information, astronomers believe that the X-ray emission could be caused by either one of two different effects. One option is jets from the supermassive black hole (not visible in this image) are interacting with interstellar gas in the galaxy and heating it enough for it to emit X-rays. In this scenario, gas heated by shocks would lie ahead of the jets. The other possibility is that bright radiation from regions close to the black hole infuses enough energy into the interstellar gas to cause it to glow. Deeper X-ray data will be needed to decide between these alternatives.

Fast Facts for 3C305:

Scale: Image is 6 arcsec across
Category: Quasars & Active Galaxies
Coordinates: (J2000) RA 14h 49m 21.37s | Dec +63° 16’ 14.00''
Constellation: Draco
Observation Date: April 7, 2008
Observation Time: 2 hours 10 minutes
Obs. ID: 9330
Color Code: X-ray (Red); Optical (Cyan); Radio (Blue)
Instrument: ACIS
Distance Estimate: About 592 million light years

Wednesday, May 13, 2009

Let the Planet Hunt Begin

Artist concept of Kepler
Image credit: NASA

Kepler Mission Status Report

NASA's Kepler spacecraft has begun its search for other Earth-like worlds. The mission, which launched from Cape Canaveral, Fla., on March 6, will spend the next three-and-a-half years staring at more than 100,000 stars for telltale signs of planets. Kepler has the unique ability to find planets as small as Earth that orbit sun-like stars at distances where temperatures are right for possible lakes and oceans.

"Now the fun begins," said William Borucki, Kepler science principal investigator at NASA's Ames Research Center, Moffett Field, Calif. "We are all really excited to start sorting through the data and discovering the planets."

Scientists and engineers have spent the last two months checking out and calibrating the Kepler spacecraft. Data have been collected to characterize the imaging performance as well as the noise level in the measurement electronics. The scientists have constructed the list of targets for the start of the planet search, and this information has been loaded onto the spacecraft.

"If Kepler got into a staring contest, it would win," said James Fanson, Kepler project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The spacecraft is ready to stare intently at the same stars for several years so that it can precisely measure the slightest changes in their brightness caused by planets." Kepler will hunt for planets by looking for periodic dips in the brightness of stars -- events that occur when orbiting planets cross in front of their stars and partially block the light.

The mission's first finds are expected to be large, gas planets situated close to their stars. Such discoveries could be announced as early as next year.

Kepler is a NASA Discovery mission. NASA Ames Research Center, Moffett Field, Calif., is the home organization of the science principal investigator, and is responsible for the ground system development, mission operations and science data analysis. JPL manages the Kepler mission development. Ball Aerospace & Technologies Corp. of Boulder, Colo., is responsible for developing the Kepler flight system and supporting mission operations.

For more information about the Kepler mission, visit: and .

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

Michael Mewhinney 650-604-3937
NASA's Ames Research Center, Moffett Field, Calif.

Spitzer Catches Star Cooking Up Comet Crystals

Credit: NASA/JPL-Caltech/P. Ábrahám (Konkoly Obs., Hungarian Academy of Sciences)

Scientists have long wondered how tiny silicate crystals, which need sizzling high temperatures to form, have found their way into frozen comets, born in the deep freeze of the solar system's outer edges. The crystals would have begun as non-crystallized silicate particles, part of the mix of gas and dust from which the solar system developed.

A team of astronomers believes they have found a new explanation for both where and how these crystals may have been created, by using NASA's Spitzer Space Telescope to observe the growing pains of a young, sun-like star. Their study results, which appear in the May 14 issue of Nature, provide new insight into the formation of planets and comets.

The researchers from Germany, Hungary and the Netherlands found that silicate appears to have been transformed into crystalline form by an outburst from a star. They detected the infrared signature of silicate crystals on the disk of dust and gas surrounding the star EX Lupi during one of its frequent flare-ups, or outbursts, seen by Spitzer in April 2008. These crystals were not present in Spitzer's previous observations of the star's disk during one of its quiet periods.

"We believe that we have observed, for the first time, ongoing crystal formation," said one of the paper's authors, Attila Juhasz of the Max-Planck Institute for Astronomy in Heidelberg, Germany. "We think that the crystals were formed by thermal annealing of small particles on the surface layer of the star's inner disk by heat from the outburst. This is a completely new scenario about how this material could be created."

Annealing is a process in which a material is heated to a certain temperature at which some of its bonds break and then re-form, changing the material's physical properties. It is one way that silicate dust can be transformed into crystalline form.

Scientists previously had considered two different possible scenarios in which annealing could create the silicate crystals found in comets and young stars' disks. In one scenario, long exposure to heat from an infant star might anneal some of the silicate dust inside the disk's center. In the other, shock waves induced by a large body within the disk might heat dust grains suddenly to the right temperature to crystallize them, after which the crystals would cool nearly as quickly.

What Juhasz and his colleagues found at EX Lupi didn't fit either of the earlier theories. "We concluded that this is a third way in which silicate crystals may be formed with annealing, one not considered before," said the paper's lead author, Peter Abraham of the Hungarian Academy of Sciences' Konkoly Observatory, Budapest, Hungary.

EX Lupi is a young star, possibly similar to our sun four or five billion years ago. Every few years, it experiences outbursts, or eruptions, that astronomers think are the result of the star gathering up mass that has accumulated in its surrounding disk. These flare-ups vary in intensity, with really big eruptions occurring every 50 years or so.

The researchers observed EX Lupi with Spitzer's infrared spectrograph in April 2008. Although the star was beginning to fade from the peak of a major outburst detected in January, it was still 30 times brighter than when it was quiet. When they compared this new view of the erupting star with Spitzer measurements made in 2005 before the eruption began, they found significant changes.

In 2005, the silicate on the surface of the star's disk appeared to be in the form of amorphous grains of dust. In 2008, the spectrum showed the presence of crystalline silicate on top of amorphous dust. The crystals appear to be forsterite, a material often found in comets and in protoplanetary disks. The crystals also appear hot, evidence that they were created in a high-temperature process, but not by shock heating. If that were the case, they would already be cool.

"At outburst, EX Lupi became about 100 times more luminous," said Juhasz. "Crystals formed in the surface layer of the disk but just at the distance from the star where the temperature was high enough to anneal the silicate--about 1,000 Kelvin (1,340 degrees Fahrenheit)--but still lower than 1,500 Kelvin (2,240 degrees Fahrenheit). Above that, the dust grains will evaporate." The radius of this crystal formation zone, the researchers note, is comparable to that of the terrestrial-planet region in the solar system.

"These observations show, for the first time, the actual production of crystalline silicates like those found in comets and meteorites in our own solar system," said Spitzer Project Scientist Michael Werner of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "So what we see in comets today may have been produced by repeated bursts of energy when the sun was young."

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory