Sunday, November 30, 2008

Orion - Infrared

Credits: Infrared Processing and Analysis Center, Caltech/JPL 

The familiar winter sky constellation Orion takes on a spectacular guise in the infrared, as seen in this false-color image constructed from data collected by IRAS--the Infrared Astronomical Satellite. This picture, covering about 30 degrees x 24 degrees is a composite of IRAS wavelength band data centered at 12 microns, 60 microns, and 100 microns. New processing techniques have been used to enhance faint details and remove the instrumental artifacts (stripes) seen in earlier IRAS images. The warmest features, e.g.~the stars, are brightest at 12 microns. This emission is coded blue. The interstellar dust is cooler and shines brighter at 60 microns (coded green) and 100 microns (coded red).

The bright yellow region in the lower right of the image is the Sword of Orion, containing the Great Orion Nebula (M42 and M43). Above it to the left is the nebulosity around the belt star Zeta Orionis which contains the often photographed Horsehead Nebula (barely visible as a small indentation on the right side). Higher and to the left is M78, a reflection nebula. The Rosette Nebula is the brightest object near the left margin of the picture.

Most of the visually bright stars of Orion are not prominent in the infrared. However, Betelgeuse can be easily seen in the upper center of the picture as a blue-white dot (the faint tail is an instrumental artifact). The large ring to the right of Betelgeuse is the remnant of a supernova explosion, centered around the star Lambda Orionis. These rings are quite common in the IRAS sky. Another one, fainter and larger, can be seen in the lower left quadrant of the image.

Thursday, November 27, 2008

Galaxies in the River

Credit & Copyright: Robert Gendler, Jan-Erik Ovaldsen,
Allan Hornstrup, IDA
Image data: ESO/Danish 1.5m telescope at La Silla, Chile - 2008

Large galaxies grow by eating small ones. Even our own galaxy practices galactic cannibalism, absorbing small galaxies that get too close and are captured by the Milky Way's gravity.

In fact, the practice is common in the universe and well illustrated by this striking pair of interacting galaxies from the banks of the southern constellation Eridanus (The River).

Located over 50 million light years away, the large, distorted spiral NGC 1532 is seen locked in a gravitational struggle with dwarf galaxy NGC 1531, a struggle the smaller galaxy will eventually lose. Seen edge-on, spiral NGC 1532 spans about 100,000 light-years.

The NGC 1532/1531 pair is thought to be similar to the system of face-on spiral and small companion known as M51, the Whirlpool Galaxy.

APOD - Astronomy Picture of the Day

Tuesday, November 25, 2008

Strangled spiral galaxies

Image credit: M. Barden, C. Wolf, M. Gray and the STAGES team

These images of galaxies from the STAGES survey show how a newly discovered population of red spiral galaxies on the outskirts of crowded regions in the Universe may be a missing link in our understanding of galaxy evolution.

Large numbers of these "red spirals" were uncovered independently by two UK-led international collaborations: Galaxy Zoo, which uses volunteers from the general public to classify enormous numbers of galaxies; and STAGES, which uses images from the Hubble Space Telescope to look in detail at the Abell 901/902 supercluster system.

The red spiral galaxies (centre) are still disk-like and recognizably spiral in shape, their spiral arms are smooth than "normal" spiral galaxies (left). Furthermore, their colour is as red as seen in old elliptical galaxies (right). Astronomers from both teams believe these red spirals are objects in transition, where star formation has been shut off by interactions with its environment.

The STAGES results are led by Christian Wolf and will appear in a forthcoming issue of the Monthly Notices of the Royal Astronomical Society.


Hubble captures views of mammoth stars

Mammoth stars seen by Hubble
Credits: NASA, ESA and Jesús Maíz Apellániz
(Instituto de Astrofísica de Andalucía, Spain)

Two of our galaxy's most massive stars, until recently shrouded in mystery, have been viewed by the NASA/ESA Hubble Space Telescope, unveiling greater detail than ever before.

The image shows a pair of colossal stars, WR 25 and Tr16-244, located within the open cluster Trumpler 16. This cluster is embedded within the Carina Nebula, an immense cauldron of gas and dust that lies approximately 7500 light-years from Earth. The Carina Nebula contains several ultra-hot stars, including these two star systems and the famous blue star Eta Carinae, which has the highest luminosity yet confirmed.


The image shows a pair of colossal stars, WR 25 and Tr16-244, located within the open cluster Trumpler 16. This cluster is embedded within the Carina Nebula, an immense cauldron of gas and dust that lies approximately 7500 light-years from Earth. The Carina Nebula contains several ultra-hot stars, including these two star systems and the famous blue star Eta Carinae, which has the highest luminosity yet confirmed.

These stars are very bright and they produce incredible amounts of heat, emitting most of their radiation in the ultraviolet and appearing blue in colour. They are so powerful that they burn through their hydrogen fuel source faster than other types of stars, leading to a ‘live fast, die young’ stellar lifestyle.

WR 25 is the brightest, situated near the centre of the image. The neighbouring Tr16-244 is the third brightest, just to the upper left of WR 25. The second brightest, to the left of WR 25, is a low-mass star located much closer to Earth than the Carina Nebula. Stars like WR 25 and Tr16-244 are relatively rare compared to other, cooler types. They interest astronomers because they are associated with star-forming nebulae, and influence the structure and evolution of galaxies.

The multiple-star system of Tr16-244
Credits: NASA, ESA and Jesús Maíz Apellániz

(Instituto de Astrofísica de Andalucía, Spain)

WR 25 is the brightest, situated near the centre of the image. The neighbouring Tr16-244 is the third brightest, just to the upper left of WR 25. The second brightest, to the left of WR 25, is a low-mass star located much closer to Earth than the Carina Nebula. Stars like WR 25 and Tr16-244 are relatively rare compared to other, cooler types. They interest astronomers because they are associated with star-forming nebulae, and influence the structure and evolution of galaxies.

WR 25 is likely to be the most massive and interesting of the two. Its true nature was revealed two years ago when an international group of astronomers led by Roberto Gamen, then at the Universidad de La Serena in Chile, discovered that it is composed of at least two stars. The more massive is a Wolf-Rayet star and may weigh more than 50 times the mass of our Sun. It is losing mass rapidly through powerful stellar winds that have expelled the majority of its outermost hydrogen-rich layers, while its more mundane binary companion is probably about half as massive as the Wolf-Rayet star, and orbits it once every 208 days.

Massive stars are usually formed in compact clusters. Often, the individual stars are physically so close to each other that it is very difficult to resolve them in telescopes as separate objects. These Hubble observations have revealed that the Tr16-244 system is actually a triple star.

Wide-field image showing the region of WR 25 and Tr16-244
Credits: NASA, ESA and Jesús Maíz Apellániz
(Instituto de Astrofísica de Andalucía, Spain)

Two of the stars are so close to each other that they look like a single object, but Hubble's Advanced Camera for Surveys shows them as two (see the separate image). The third star takes tens or hundreds of thousands of years to orbit the other two. The brightness and proximity of the components of such massive double and triple stars make it particularly challenging to analyse the properties of massive stars.

WR 25 and Tr16-244 are the likely sources of radiation that is causing a giant gas globule within the Carina Nebula to slowly evaporate away into space, while possibly inducing the formation of new stars within it (see separate image). The radiation is also thought to be responsible for the globule's interesting shape, prominently featured in earlier Hubble images, which looks like a hand with a ‘defiant’ finger pointing towards WR 25 and Tr16-244.

These new observations were obtained by a team including astronomers from US, Chilean, Spanish, and Argentinian institutions and led by Jesús Maíz Apellániz from the Instituto de Astrofísica de Andalucía in Spain. They are using Hubble along with ground-based observatories in Spain, Chile, and Argentina to build a comprehensive catalogue of observations of all the massive stars in the Galaxy that are detectable at visible wavelengths.

Notes for editors:
The Hubble Space Telescope is a project of international cooperation between NASA and ESA.

Contacts:
Jesús Maíz Apellániz, Instituto de Astrofísica de Andalucía, Spain
E-mail: Jmaiz @ iaa.es

Lars Lindberg Christensen, Hubble/ESA, Garching, Germany
E-mail: Lars @ eso.org

M101 - A Pinwheel in X-rays

M101

With a diameter of about 170,000 light years, the galaxy Messier 101 (M101) is a swirling spiral of stars, gas, and dust whose diameter is nearly twice that of our Milky Way Galaxy. Its orientation allows telescopes to see the spiral structure of the galaxy face-on, giving inspiration for its nickname of the Pinwheel Galaxy. M101 is found in the Ursa Major constellation and is at a distance of about 25 million light years from Earth.

This Chandra image of M101 is one of the longest exposures ever obtained of a spiral galaxy in X-rays. The point-like sources include binary star systems containing black holes and neutron stars, and the remains of supernova explosions. Other sources of X-rays include hot gas in the arms of the galaxy and clusters of massive stars. These X-ray observations of M101 will be used to establish a valuable X-ray profile of a galaxy similar to the Milky Way. This will help astronomers better understand the evolutionary paths that produce black holes, and provide a baseline for interpreting the observations of distant galaxies.

Fast Facts for M101:
Credit: NASA/CXC/JHU/K.Kuntz et al.
Scale Image: is 16.8 arcmin across.
Category: Normal Galaxies & Starburst Galaxies

Coordinates: (J2000) RA 14h 03m 12.59s | Dec 54° 20' 56.70''

Constellation: Ursa Major

Observation Date: 03/26/2000 - 01/01/2005 with 26 pointings

Observation Time: 11 days 10 hours

Obs. ID: 934, 2065, 4731-4737, 5296-5297, 5300, 5309, 5322-5323, 5337-5340, 6114-6115, 6118, 6152, 6169-6170, 6175

Color: Code Purple (0.45 - 1.00 keV); Blue (1.00 - 2.00 keV)

Instrument: ACIS

Also Known As NGC 5457, The Pinwheel Galaxy

Distance Estimate: About 25 million light years

Saturday, November 22, 2008

Beta Pictoris planet finally imaged?

ESO PR Photo 42b/08
Beta Pictoris as seen in infrared light - annotated

Candidate planetary systems imaged

This diagramme compares the various candidate planetary systems that have been imaged for now, with our Solar System. Indicated are the star and the position of the imaged candidate planets. The probable planet around Beta Pictoris is the closest to its host star of all extra-solar planets yet imaged, and is comparable to Saturn as far as its distance is concerned. The scale is the distance between the Earth and the Sun. A list of all candidate exoplanets directly imaged can be found at http://exoplanet.eu/catalog-imaging.php
Credit: ESO


A team of French astronomers using ESO's Very Large Telescope have discovered an object located very close to the star Beta Pictoris, and which apparently lies inside its disc. With a projected distance from the star of only 8 times the Earth-Sun distance, this object is most likely the giant planet suspected from the peculiar shape of the disc and the previously observed infall of comets onto the star. It would then be the first image of a planet that is as close to its host star as Saturn is to the Sun.

The hot star Beta Pictoris is one of the best-known examples of stars surrounded by a dusty 'debris' disc. Debris discs are composed of dust resulting from collisions among larger bodies like planetary embryos or asteroids. They are a bigger version of the zodiacal dust in our Solar System. Its disc was the first to be imaged — as early as 1984 — and remains the best-studied system. Earlier observations showed a warp of the disc, a secondary inclined disc and infalling comets onto the star. "These are indirect, but tell-tale signs that strongly suggest the presence of a massive planet lying between 5 and 10 times the mean Earth-Sun distance from its host star," says team leader Anne-Marie Lagrange. "However, probing the very inner region of the disc, so close to the glowing star, is a most challenging task."

In 2003, the French team used the NAOS-CONICA instrument (or NACO [1]), mounted on one of the 8.2 m Unit Telescopes of ESO's Very Large Telescope (VLT), to benefit from both the high image quality provided by the Adaptive Optics system at infrared wavelengths and the good dynamics offered by the detector, in order to study the immediate surroundings of Beta Pictoris.

Recently, a member of the team re-analysed the data in a different way to seek the trace of a companion to the star. Infrared wavelengths are indeed very well suited for such searches. "For this, the real challenge is to identify and subtract as accurately as possible the bright stellar halo," explains Lagrange. "We were able to achieve this after a precise and drastic selection of the best images recorded during our observations."

The strategy proved very rewarding, as the astronomers were able to discern a feeble, point-like glow well inside the star's halo. To eliminate the possibility that this was an artefact and not a real object, a battery of tests was conducted and several members of the team, using three different methods, did the analysis independently, always with the same success. Moreover, the companion was also discovered in other data sets, further strengthening the team's conclusion: the companion is real.

"Our observations point to the presence of a giant planet, about 8 times as massive as Jupiter and with a projected distance from its star of about 8 times the Earth-Sun distance, which is about the distance of Saturn in our Solar System [2]," says Lagrange.

"We cannot yet rule out definitively, however, that the candidate companion could be a foreground or background object," cautions co-worker Gael Chauvin. "To eliminate this very small possibility, we will need to make new observations that confirm the nature of the discovery."

The team also dug into the archives of the Hubble Space Telescope but couldn't see anything, "while most possible foreground or background objects would have been detected", remarks another team member, David Ehrenreich.

The fact that the candidate companion lies in the plane of the disc also strongly implies that it is bound to the star and its proto-planetary disc.

"Moreover, the candidate companion has exactly the mass and distance from its host star needed to explain all the disc's properties. This is clearly another nail in the coffin of the false alarm hypothesis," adds Lagrange.

When confirmed, this candidate companion will be the closest planet from its star ever imaged. In particular, it will be located well inside the orbits of the outer planets of the Solar System. Several other planetary candidates have indeed been imaged, but they are all located further away from their host star: if located in the Solar System, they would lie close or beyond the orbit of the farthest planet, Neptune. The formation processes of these distant planets are likely to be quite different from those in our Solar System and in Beta Pictoris.

"Direct imaging of extrasolar planets is necessary to test the various models of formation and evolution of planetary systems. But such observations are only beginning. Limited today to giant planets around young stars, they will in the future extend to the detection of cooler and older planets, with the forthcoming instruments on the VLT and on the next generation of optical telescopes," concludes team member Daniel Rouan.

Only 12 million years old, the 'baby star' Beta Pictoris is located about 70 light-years away towards the constellation Pictor (the Painter).

Notes

[1] NACO is one of the instruments on ESO's VLT that make use of Adaptive Optics (AO). Such systems work by means of a computer-controlled deformable mirror that counteracts the image distortion induced by atmospheric turbulence (see e.g. ESO Press Release 25/01).

[2] The astronomers can only see the projected separation between the star and the planet (that is, the separation projected on the plane of the sky).

More Information:
"A probable giant planet imaged in the β Pictoris disk. VLT/NACO Deep L-band imaging", by A.-M. Lagrange et al., 2008, Letter to the Editor of Astronomy and Astrophysics, in press. (a PDF file can be downloaded here)
The team is composed of A.-M. Lagrange, G. Chauvin, D. Ehrenreich, and D. Mouillet (Laboratoire d'Astrophysique de l'Observatoire de Grenoble, France), D. Gratadour, G. Rousset, D. Rouan and E. Gendron (LESIA, Observatoire de Paris, France), T. Fusco, and L. Mugnier (Office National d'Etudes et de Recherches Aérospatiales, Chatillon, France), F. Allard (Centre de Recherche Astronomique de Lyon, France), and the NAOS Consortium.

Contacts:

Anne-Marie Lagrange and Gael Chauvin
LAOG, Grenoble, France
E-mail: anne-marie.lagrange@obs.ujf-grenoble.fr, gael.chauvin@obs.ujf-grenoble.fr
Phone: +33 4 7651 4203, +33 4 7663 5803

Daniel Rouan
LESIA, Observatoire de Paris, France
E-mail: daniel.rouan@obspm.fr
Phone: +33 1 4507 7715

ESO Press Officer: Dr. Henri Boffin - +49 89 3200 6222 - hboffin@eso.org
ESO Press Officer in Chile: Valentina Rodriguez - +56 2 463 3123 - vrodrigu@eso.org

Thursday, November 20, 2008

Hubble Resolves Puzzle about Loner Starburst Galaxy

Science Credit: NASA, ESA, A. Aloisi (STScI/ESA),
 J. Mack and A. Grocholski (STScI), 
M. Sirianni (STScI/ESA), R. van der Marel (STScI), L. Angeretti, 
D. Romano, and M. Tosi (INAF-OAB), and F. Annibali, 
L. Greggio, and E. Held (INAF-OAP) 

Image Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), 
and A. Aloisi (STScI/ESA)- STScI-2008-38

Astronomers have long puzzled over why a small, nearby, isolated galaxy is pumping out new stars faster than any galaxy in our local neighborhood.

Now NASA's Hubble Space Telescope has helped astronomers solve the mystery of the loner starburst galaxy, called NGC 1569, by showing that it is one and a half times farther away than astronomers thought.

The extra distance places the galaxy in the middle of a group of about 10 galaxies centered on the spiral galaxy IC 342. Gravitational interactions among the group's galaxies may be compressing gas in NGC 1569 and igniting the star-birthing frenzy.

"Now the starburst activity seen in NGC 1569 makes sense, because the galaxy is probably interacting with other galaxies in the group," said the study's leader, Alessandra Aloisi of the Space Telescope Science Institute in Baltimore, Md., and the European Space Agency. "Those interactions are probably fueling the star birth."

The farther distance not only means that the galaxy is intrinsically brighter, but also that it is producing stars two times faster than first thought. The galaxy is forming stars at a rate more than 100 times higher than the rate in the Milky Way. This high star-formation rate has been almost continuous for the past 100 million years.

Discovered by William Herschel in 1788, NGC 1569 is home to three of the most massive star clusters ever discovered in the local universe. Each cluster contains more than a million stars.

"This is a prime example of the type of massive starbursts that drive the evolution of galaxies in the distant and young universe," said team member Roeland van der Marel of the Space Telescope Science Institute. "Starburst galaxies can only be studied in detail in the nearby universe, where they are much rarer. Hubble observations of our galactic neighborhood, including this study, are helping astronomers put together a complete picture of the galaxies in our local universe. Put the puzzle pieces in the right place, as for NGC 1569, and the picture makes much more sense."

Aloisi and her team actually discovered the new distance by accident. They were using Hubble's Advanced Camera for Surveys to hunt in NGC 1569 for the kind of red giant stars (stars near the ends of their lives) that shine because of fusion of helium nuclei in their cores. These stars are dimmer than bright red giants without helium burning, but when detected, they can be used to estimate the galaxy's age.

"When we found no obvious trace of them, we suspected that the galaxy was farther away than originally believed," said Aaron Grocholski of the Space Telescope Science Institute and the lead author on a paper describing the results. "We could only see the brightest red giant stars, but we were able to use these stars to recalibrate the galaxy's distance." Bright red giants are reliable "standard candles" for measuring distance because they all shine at the same brightness. Once astronomers know a star's true brightness, they can calculate its distance from Earth.

Previous estimates of the galaxy's distance made with ground-based telescopes were unreliable because they looked at the galaxy's crowded core and were unable to resolve individual red giant stars.

The Hubble study observed both the galaxy's cluttered core and its sparsely populated outer fringes. The sharpness of Hubble's Advanced Camera pinpointed individual red giants, which led to a precise distance to the galaxy. Astronomers measured the galaxy's distance at nearly 11 million light-years away, about 4 million light-years farther than the old distance.

"This was a serendipitous discovery," Aloisi said. "Hubble didn't go deep enough to see the faintest red giant stars we were hunting for because the galaxy is farther away than we thought. However, by capturing the entire population of the brightest red giant stars, we were able to calculate a precise distance to NGC 1569 and resolve the puzzle about the galaxy's extreme starburst activity."

The results were published in the Oct. 20 issue of the Astrophysical Journal Letters.

The science team for the NGC 1569 observations consists of Alessandra Aloisi and Marco Sirianni (STScI/ESA), Aaron Grocholski, Jennifer Mack, and Roeland van der Marel (STScI), Luca Angeretti, Donatella Romano, and Monica Tosi (INAF-OAB), and Francesca Annibali, Laura Greggio, and Enrico Held (INAF-OAP).

CONTACT:
Donna Weaver/Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

Alessandra Aloisi
Space Telescope Science Institute, Baltimore, Md./European Space Agency
410-338-4519
aloisi@stsci.edu

Wednesday, November 19, 2008

Akari infrared space telescope: latest science highlights

Betelgeuse creates a splash
Credits: Ueta et al, PASJ, 2008

The Akari infrared surveyor, a Japanese Aerospace Exploration Agency mission with ESA participation, has returned a host of new results. From splashes in cosmic rivers of dust and gas to supernova remnants, the mission has been uncovering secrets of the cold and dusty Universe.

Bow shock around Betelgeuse
Credits: JAXA

Splashes in the interstellar medium

The interstellar medium, a tenuous mix of gas and tiny solid dust particles, permeates space. As stars age, they spew out gas and dust in a flow called stellar wind, which eventually mixes with the interstellar medium. At the interface between stellar wind and the interstellar medium, physical conditions such as density and pressure change dramatically, creating what is called a bow shock.

Akari observations of Betelgeuse, a bright red supergiant star located in the constellation Orion about 200 light-years from Earth, show the star making a big splash by creating a bow shock as it crosses the interstellar medium. Researchers have found a strong flow of the interstellar medium around the star which originates from star-forming regions in Orion's Belt.

Stars condense out of the interstellar medium at birth, and old stars like Betelgeuse spew out matter into surrounding space, enriching the interstellar medium. This process is repeated by generations of stars and assists the chemical evolution of the Universe. Akari has found a number of such bow shocks and investigation into these processes will further our understanding of the cosmic recycling of matter.

Globular cluster NGC 1261

Mysterious missing dust

Globular clusters are spherical groups of a hundred thousand to a million stars that are found throughout our and other galaxies. A one-off star formation process in each system about 10 thousand million years ago triggered the formation of these globular clusters.

Aged stars often eject large amounts of gas and dust into interstellar space, which eventually forms a new generation of stars and planets, so scientists expected to detect cold dust in the 12 globular clusters observed by Akari. But high-sensitivity observations with the Far-Infrared Surveyor onboard Akari yielded no evidence of cold dust in any of the clusters.

One possibility is that the dust accreted on to the stellar surface. But such a process would take much longer than the lifetime of the cluster. The new Akari observations pose new questions to astronomers.

Supernova remnants in the Large Magellanic Cloud
Credits: Seok et al., PASJ 2008

About this image: Three-colour composite images of eight supernova remnants in the Large Magellanic Cloud composed of images taken at 7 (blue), 11 (green) and 15 (red) micrometers, with the near- and mid-Infrared Camera (IRC) onboard Akari. Contours indicate the intensity of the X-ray emission observed by the NASA's Chandra X-ray observatory. The line at the bottom of each image indicates a distance of 20 light-years. 

Warm dust in supernova remnants

At the end of their lives, massive stars explode in a catastrophic explosion, returning a huge amount of energy and heavy elements into space. Scientists believe that the explosion destroys the surrounding interstellar dust grains, leaving behind a supernova remnant which can be studied to understand the explosion itself as well as its role on the evolution of the interstellar medium.

The study of interstellar dust is important because that very dust is a seed of another star as well as of a planet like Earth.

The Large Magellanic Cloud is a companion galaxy of the Milky Way located at a distance of about 160 000 light-years from us. Its relatively short distance and unique location provides a unique view of the entire galaxy from Earth and the possibility to study the interstellar medium.

Akari observations of about eight of the 20 reported supernova remnants in the region have revealed unexpected details.

Akari has found that supernova remnants in the Large Magellanic Cloud are surrounded by previously-unknown warm dust. This suggests that some dust grains survive the shock of the supernova explosion. Further analysis with the Akari data will greatly improve our knowledge on supernova remnants and their influence on their surroundings.

Notes for editors:

Akari was launched on 21 February 2006 and began its scientific observations in May 2006.

Its on-board supply of liquid helium ran out on 26 August 2007, and the spacecraft entered a new mission phase. The liquid helium was required to keep Akari cold enough to observe in the far-infrared. The warm phase now uses the surviving instrument, the near-infrared mode of the infrared camera, which can operate under the warmer conditions provided by the on-board mechanical cooler for near-infrared observations.

Akari achieved its planned ‘cold’ lifetime of 550 days. During this time, it conducted an all-sky survey in the infrared, covering about 94 % of the entire sky, with larger wavelength coverage and better spatial resolution than its predecessor, IRAS. The first version of the resulting catalogue has just been released to the project teams. The public release is planned for autumn 2009. Akari also carried out more than five thousand individual pointed observations.

Akari is a Japanese Aerospace Exploration Agency, JAXA mission with several participating partners: Nagoya University, The University of Tokyo and National Astronomical Observatory Japan; ESA; Imperial College London, the University of Sussex and The Open University, UK; the University of Groningen/SRON, The Netherlands; the Seoul National University, Korea. The far-infrared detectors were developed in collaboration with the National Institute of Information and Communications Technology Japan.

ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany, provided the mission with ground support through its ground station in Kiruna, for several passes per day in the cold phase of the mission. ESA’s European Space Astronomy Centre (ESAC), Madrid, Spain provides expertise and support for the sky-survey data processing through the pointing reconstruction – this allows the determination of accurate astronomical positions for each of the sources detected. The goal is to accelerate the production of the survey catalogues as a legacy for Herschel and Planck.

ESAC also provides user support for European astronomers who have been granted observing opportunities. The 10% of observing time obtained from this collaboration resulted in 400 observations in the cold phase, covering various fields of astronomy, from comets to cosmology. A second call for proposals for 700 observations in the first year of the warm phase was issued in May 2008. The open time observations, included the European ones, started on 15 October 2008.

For more information:
Alberto Salama, ESA Akari Project Scientist
Email: Alberto.Salama @ esa.int

M84 - Huge Russian Dolls Surrounding a Galaxy

Credit: X-ray (NASA/CXC/MPE/A.Finoguenov et al.);
Radio (NSF/NRAO/VLA/ESO/R.A.Laing et al); Optical (SDSS)

This composite image shows M84, a massive elliptical galaxy in the Virgo Cluster, about 55 million light years from Earth. Hot gas around M84 is shown in a Chandra X-ray Observatory image in blue and a radio image from the Very Large Array is shown in red. A background image from the Sloan Digital Sky Survey is shown in yellow and white.

A number of bubbles are visible in the hot gas, outlined with blue X-ray emission. These bubbles were blown by relativistic particles generated by the central supermassive black hole in M84. These particles travel outwards in the form of a two-sided jet. Because smaller bubbles are found inside large bubbles, the impression given by the image is that of Russian dolls, where smaller dolls can be found inside large ones. These nested bubbles provide clear evidence for repeated outbursts from the central black hole.

Supercomputer simulations of the interaction of supermassive black holes with surrounding gas can explain how such "Russian dolls" are created. The simulations reveal the nested bubbles associated with the termination of the jet and their complex interaction with the surrounding gas, somewhat similar to the effervescent bubbles in a glass of champagne.

The dissipation of energy by sound and shock waves generated by these outbursts, as well as the additional motions they generate, are believed to be heating the gas surrounding M84. This slows down the cooling of the gas and suppresses the formation of new stars. Unless a black hole experiences a single but extremely powerful episode of activity, multiple outbursts are needed to suppress the formation of new stars and to maintain a balance between cooling and heating over long periods of time.

The observations also show that the top bubble is bursting and the hot relativistic gas, shown in red, is spilling out to the surrounding medium. The mixing of this hot gas with the cooler gas in the galaxy is an additional mode of heating of the surrounding gas by supermassive black holes that has not previously been seen so clearly.

These results address a larger question of why galaxies stop growing after reaching a certain mass, despite containing large quantities of gas that can potentially cool and form new stars. If uninhibited, such cooling process would lead to the formation of many new stars and much bigger galaxies than are observed. Outbursts generated by supermassive black holes like those in M84 provide at least one explanation for this lack of "mega-galaxies".

Alexis Finoguenov of the Max-Planck Institute for Extraterrestrial Physics and University of Maryland, led this study. The co-authors are Mateusz Ruszkowski of the University of Michigan, Marcus Bruggen of Jacobs University in Bremen, Germany, and Christine Jones, Alexey Vikhlinin and Eric Mandel of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

M84 - Animation Simulation of Interaction of Black Hole

Fast Facts for M84:
Scale: Image is 9 arcmin across.
Category: Normal Galaxies & Starburst Galaxies
Coordinates: (J2000) RA 12h 25m 03.743s | Dec +12° 53' 13.14''
Constellation: Virgo
Observation Date: 05/19/2000 - 11/07/2005 with three pointings
Observation Time: 26 hours
Obs. ID: 803, 5908, 6131
Color Code: X-ray (Blue); Radio (Red); Optical (Yellow)
Instrument: ACIS
Also Known As NGC 4374
Distance Estimate: About 55 million light years

Tuesday, November 18, 2008

Astronomers detect matter torn apart by black hole

ESO PR Photo 41c/08
Credit: ESO/APEX/2MASS/A. Eckart et al. , ESO/L. Calçada


About this image:
Left:- This is a colour composite image of the central region of our Milky Way galaxy, about 26 000 light years from Earth. Giant clouds of gas and dust are shown in blue, as detected by the LABOCA instrument on the Atacama Pathfinder Experiment (APEX) telescope at submillimetre wavelengths (870 micron). The image also contains near-infrared data from the 2MASS project at K-band (in red), H-band (in green), and J-band (in blue). The image shows a region approximately 100 light-years wide.

Rigth:- This series of three images shows an artist’s impression of a bright “blob” of gas in the disk of material surrounding the black hole in the centre of our Galaxy, Sagittarius A*. This blob of material is responsible for the flares detected by the researchers. As the blob orbits the black hole, it is stretched out, and this expansion over time causes the delay between flares being detected at near-infrared wavelengths (with the VLT) and at submillimetre wavelengths (with APEX).

VLT and APEX team up to study flares from the black hole at the Milky Way's core

Astronomers have used two different telescopes simultaneously to study the violent flares from the supermassive black hole in the centre of the Milky Way. They have detected outbursts from this region, known as Sagittarius A*, which reveal material being stretched out as it orbits in the intense gravity close to the central black hole.

The team of European and US astronomers used ESO's Very Large Telescope (VLT) and the Atacama Pathfinder Experiment (APEX) telescope, both in Chile, to study light from Sagittarius A* at near-infrared wavelengths and the longer submillimetre wavelengths respectively. This is the first time that astronomers have caught a flare with these telescopes simultaneously. The telescopes' location in the southern hemisphere provides the best vantage point for studying the Galactic Centre.

"Observations like this, over a range of wavelengths, are really the only way to understand what's going on close to the black hole," says Andreas Eckart of the University of Cologne, who led the team.

Sagittarius A* is located at the centre of our own Milky Way Galaxy at a distance from Earth of about 26 000 light-years. It is a supermassive black hole with a mass of about four million times that of the Sun. Most, if not all, galaxies are thought to have a supermassive black hole in their centre.

"Sagittarius A* is unique, because it is the nearest of these monster black holes, lying within our own galaxy," explains team member Frederick K. Baganoff of the Massachusetts Institute of Technology (MIT) in Cambridge, USA. "Only for this one object can our current telescopes detect these relatively faint flares from material orbiting just outside the event horizon."

The emission from Sagittarius A* is thought to come from gas thrown off by stars, which then orbits and falls into the black hole.

Making the simultaneous observations required careful planning between teams at the two telescopes. After several nights waiting at the two observatory sites, they struck lucky.

"At the VLT, as soon as we pointed the telescope at Sagittarius A* we saw it was active, and getting brighter by the minute. We immediately picked up the phone and alerted our colleagues at the APEX telescope," says Gunther Witzel, a PhD student from the University of Cologne.

Macarena García-Marín, also from Cologne, was waiting at APEX, where the observatory team had made a special effort to keep the instrument on standby. "As soon as we got the call we were very excited and had to work really fast so as not to lose crucial data from Sagittarius A*. We took over from the regular observations, and were in time to catch the flares," she explains.

Over the next six hours, the team detected violently variable infrared emission, with four major flares from Sagittarius A* . The submillimetre-wavelength results also showed flares, but, crucially, this occurred about one and a half hours after the infrared flares.

The researchers explain that this time delay is probably caused by the rapid expansion, at speeds of about 5 million km/h, of the clouds of gas that are emitting the flares. This expansion causes changes in the character of the emission over time, and hence the time delay between the infrared and submillimetre flares.

Although speeds of 5 million km/h may seem fast, this is only 0.5% of the speed of light. To escape from the very strong gravity so close to the black hole, the gas would have to be travelling at half the speed of light – 100 times faster than detected – and so the researchers believe that the gas cannot be streaming out in a jet. Instead, they suspect that a blob of gas orbiting close to the black hole is being stretched out, like dough in a mixing bowl, and this is causing the expansion.

The simultaneous combination of the VLT and APEX telescopes has proved to be a powerful way to study the flares at multiple wavelengths. The team hope that future observations will let them prove their proposed model, and discover more about this mysterious region at the centre of our Galaxy.

Notes for Editors

Sagittarius A* is a compact object located at the centre of our own Milky Way Galaxy, at a distance of about 26 000 light-years from Earth. In recent years, observations of stars orbiting in its strong gravitational grip have convincingly proven that Sagittarius A* must be a supermassive black hole with a mass of about four million times that of the Sun.

The 12 m Atacama Pathfinder Experiment (APEX) telescope is located on the 5000 m high plateau of Chajnantor in the Chilean Atacama desert. APEX is a collaboration between the Max-Planck-Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. The telescope is based on a prototype antenna constructed for the ALMA project. Operation of APEX at Chajnantor is entrusted to ESO. For this project, the researchers used the LABOCA bolometer camera on APEX.

The Very Large Telescope (VLT) at the 2600 m high Cerro Paranal is ESO's premier site for observations in visible and infrared light. The VLT has four "Unit Telescopes", 8.2 m in diameter, operating with a large collection of instruments. For this project, the researchers used the NACO adaptive optics instrument on the fourth Unit Telescope, "Yepun".

This research is presented in the paper by Eckart et al., "Simultaneous NIR/sub-mm observation of flare emission from Sgr A*", to appear in Astronomy and Astrophysics. It is available online at http://arxiv.org/abs/0811.2753

The members of the international team who did this research are: A. Eckart (University of Cologne, Germany), R. Schödel (Instituto de Astrofísica de Andalucía - CSIC, Spain), M. García-Marín (University of Cologne, Germany), G. Witzel (University of Cologne, Germany), A. Weiss (MPIfR, Germany), F. K. Baganoff (MIT, USA), M. R. Morris (University of California, USA), T. Bertram (University of Cologne, Germany), M. Dovčiak (Astronomical Institute of the Academy of Sciences of the Czech Republic), D. Downes (IRAM, France), W.J. Duschl (Christian-Albrechts-Universität, Germany), V. Karas (Astronomical Institute of the Academy of Sciences of the Czech Republic), S. König (University of Cologne, Germany), T. P. Krichbaum (MPIfR, Germany), M. Krips (Harvard-Smithsonian Center for Astrophysics, USA), D. Kunneriath (University of Cologne, Germany), R.-S. Lu (MPIfR, Germany), S. Markoff (Astronomical Institute 'Anton Pannekoek', Netherlands), J. Mauerhan (University of California, USA), L. Meyer (University of California, USA), J. Moultaka (LATT, France), K. Mužić (University of Cologne, Germany), F. Najarro (Centro de Astro Biologia, Madrid, Spain), J.-U. Pott (University of California, USA), K. F. Schuster (IRAM, France), L. O. Sjouwerman (NRAO, USA), C. Straubmeier (University of Cologne, Germany), C. Thum (IRAM, France), S. Vogel (University of Maryland, USA), H. Wiesemeyer (IRAM, Spain), M. Zamaninasab (University of Cologne, Germany), J. A. Zensus (MPIfR, Germany)

Contacts
Andreas Eckart
University of Cologne, Germany
Phone: +49 221 470 3546
E-mail: eckart (at) ph1.uni-koeln.de

Fred Baganoff
Massachusetts Institute of Technology, Cambridge, USA
Phone: +1 617 253 6892
E-mail: fkb (at) space.mit.edu

Rainer Schödel
Instituto de Astrofísica de Andalucía - CSIC, Spain
Phone: +34 958 230 529
E-mail: rainer (at) iaa.es

Macarena García-Marín
University of Cologne, Germany
Phone: +49 221 470 7788
E-mail: maca (at) ph1.uni-koeln.de

Saturday, November 15, 2008

XMM-Newton and Integral clues on magnetic powerhouses

Credits: © 2008 Sky & Telescope: Gregg Dinderman

X-ray and gamma-ray data from ESA’s XMM-Newton and Integral orbiting observatories has been used to test, for the first time, the physical processes that make magnetars, an atypical class of neutron stars, shine in X-rays.

Neutron stars are remnants of massive stars (10-50 times as massive as our Sun) that have collapsed on to themselves under their own weight. Made almost entirely of neutrons (subatomic particles with no electric charge), these stellar corpses concentrate more than the mass of our Sun within a sphere about 20 km in diameter.

They are so compact that a teaspoon of neutron star stuff would weigh about one hundred million tons. Two other physical properties characterise a neutron star: their fast rotation and strong magnetic field.

Magnetars form a class of neutron stars with ultra-strong magnetic fields. With magnetic fields a thousand times stronger than that of ordinary neutron stars, they are the strongest known magnets in the cosmos.

In comparison, one would need 10 million million commonly-used hand magnets to generate a comparable magnetic field (most media used for data storage, for example, would be erased instantly if exposed to a magnetic field a mere million million times weaker).

So far, about 15 magnetars have been found. Five of them are known as soft gamma repeaters, or SGRs, because they sporadically release large, short bursts (lasting about 0.1 s) of low energy (soft) gamma rays and hard X-rays. The rest, about 10, are associated with anomalous X-ray pulsars, or AXPs. Although SGRs and AXPs were first thought to be different objects, we now know that they share many properties and that their activity is sustained by their strong magnetic fields.

Magnetars are different from ‘ordinary’ neutron stars because their internal magnetic field is thought to be strong enough to twist the stellar crust. Like in a circuit fed by a gigantic battery, this twist produces currents in the form of electron clouds which flow around the star. These currents interact with the radiation coming from the stellar surface, producing the X-rays.

Until now, scientists could not test their predictions, because it is not possible to produce such ultra-strong magnetic fields in laboratories on Earth.

To understand this phenomenon, a team led by Dr Nanda Rea from the University of Amsterdam used XMM-Newton and Integral data to search for these dense electron clouds around all known magnetars, for the first time.

Rea’s team found evidence that large electron currents do actually exist, and were able to measure the electron density which is a thousand times stronger than in a ‘normal’ pulsar. They have also measured the typical velocity at which the electron currents flow. With it, scientists have now established a link between an observed phenomenon and an actual physical process, an important clue in the puzzle of understanding these celestial objects.

The team is now working hard to develop and test more detailed models on the same line, to fully understand the behaviour of matter under the influence of such strong magnetic fields.

Notes for editors:

The team includes Dr Silvia Zane, from University College London, Prof. Roberto Turolla from the University of Padua, Prof. Maxim Lyutikov from Purdue University, and Dr Diego Gotz from CEA-Saclay.

The results appear in ‘Resonant cyclotron scattering in magnetars’ emission’, by N. Rea, S. Zane, R. Turolla, M. Lyutikov and D. Gotz, published in the Astrophysical Journal on 20 October 2008.

The XMM-Newton science teams are based in several European and US institutes, grouped into three instrument teams and the XMM-Newton Survey Science Centre (SSC). Science operations are managed at ESA’s European Space Astronomy Centre (ESAC), at Villanueva de la Cañada near Madrid, Spain. Spacecraft operations are managed at ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany.

For more information:

Nanda Rea, Anton Pannekoek Institute, University of Amsterdam
Email: N.Rea @ uva.nl

Norbert Schartel, ESA XMM-Newton Project Scientist
Email: Norbert.Schartel @ esa.int

Christoph Winkler, ESA Integral Project Scientist
Email: Christoph.Winkler @ esa.int

Thursday, November 13, 2008

Hubble Directly Observes Planet Orbiting Fomalhaut

Credit: NASA, ESA, and Z. Levay (STScI)

NASA's Hubble Space Telescope has taken the first visible-light snapshot of a planet circling another star.

Estimated to be no more than three times Jupiter's mass, the planet, called Fomalhaut b, orbits the bright southern star Fomalhaut, located 25 light-years away in the constellation Piscis Australis (the Southern Fish).

Fomalhaut has been a candidate for planet hunting ever since an excess of dust was discovered around the star in the early 1980s by NASA's Infrared Astronomy Satellite (IRAS).

In 2004, the coronagraph in the High Resolution Camera on Hubble's Advanced Camera for Surveys produced the first-ever resolved visible-light image of a large dust belt surrounding Fomalhaut. It clearly showed that this structure is in fact a ring of protoplanetary debris approximately 21.5 billion miles across with a sharp inner edge.

This large debris disk is similar to the Kuiper Belt, which encircles the solar system and contains a range of icy bodies from dust grains to objects the size of dwarf planets, such as Pluto.

Hubble astronomer Paul Kalas, of the University of California at Berkeley, and team members proposed in 2005 that the ring was being gravitationally modified by a planet lying between the star and the ring's inner edge.

Circumstantial evidence came from Hubble's confirmation that the ring is offset from the center of the star. The sharp inner edge of the ring is also consistent with the presence of a planet that gravitationally "shepherds" ring particles. Independent researchers have subsequently reached similar conclusions.

Now, Hubble has actually photographed a point source of light lying 1.8 billion miles inside the ring's inner edge. The results are being reported in the November 13 issue of Science magazine.

"Our Hubble observations were incredibly demanding. Fomalhaut b is 1 billion times fainter than the star. We began this program in 2001, and our persistence finally paid off," Kalas says.

"Fomalhaut is the gift that keeps on giving. Following the unexpected discovery of its dust ring, we have now found an exoplanet at a location suggested by analysis of the dust ring's shape. The lesson for exoplanet hunters is 'follow the dust,'" says team member Mark Clampin of NASA's Goddard Space Flight Center.

Observations taken 21 months apart by Hubble's Advanced Camera for Surveys' coronagraph show that the object is moving along a path around the star and therefore is gravitationally bound to it. The planet is 10.7 billion miles from the star, or about 10 times the distance of the planet Saturn from the sun.

The planet's upper-mass limit is constrained by the appearance of the Fomalhaut ring. If the planet were much more massive, it would distort the ring, and the effect would be observable in the ring's structure.

"It took the science team four months of analysis and theoretical modeling to determine that Fomalhaut b could not be more massive than three times the mass of Jupiter. Any more massive than that and its gravity would destroy the vast dust belt encircling the star," Kalas says.

Numerous computer simulations show that circumstellar disks will be gravitationally modified by the tug of one or more unseen planets. The Fomalhaut ring has a sharp inner edge that is likely shaped by the gravitational influence of a planet. The inner edge of our solar system's Kuiper Belt is similarly shaped by the gravitational influence of Neptune.

The planet is brighter than expected for an object of three Jupiter masses. One possibility is that it has a huge Saturn-like ring of ice and dust reflecting starlight. The ring might eventually coalesce to form moons. The ring's estimated size is comparable to the region around Jupiter that is filled with the orbits of the four largest satellites.

Because the Fomalhaut system is only 200 million years old, the planet should be a bright infrared object. That's because it is still cooling through gravitational contraction. However, ground-based telescopic observations at infrared wavelengths have not yet detected the planet. This also sets an upper limit on its mass, because the bigger the planet, the hotter and brighter it would be.

Kalas and his team first used Hubble to photograph Fomalhaut in 2004, and made the unexpected discovery of its debris disk, which scatters Fomalhaut's starlight. At the time they noted a few bright sources in the image as planet candidates. A follow-up image in 2006 showed that one of the objects is moving through space with Fomalhaut but changed position relative to the ring since the 2004 exposure. The amount of displacement between the two exposures corresponds to an 872-year-long orbit as calculated from Kepler's laws of planetary motion.

Fomalhaut moves across the sky at 0.425 arcseconds per year, which is the apparent width of a penny seen from five miles away.

The planet mysteriously dimmed by half a stellar magnitude between the 2004 and 2006 observations. This might mean that it has a hot outer atmosphere heated by bubbling convection cells on the young planet — sort of a Jupiter on steroids. Or, it might come from hot gas at the inner boundary of a ring around the planet.

The planet may have formed at its location in a primordial circumstellar disk by gravitationally sweeping up remaining gas. Or, it may have migrated outward through a game of gravitational billiards where it exchanged momentum with smaller planetary bodies. It is commonly believed that the planets Uranus and Neptune migrated out to their present orbits after forming closer to the sun and then gravitationally interacted with smaller bodies.

Fomalhaut is much hotter than our sun and is 16 times as bright. This means a planetary system could scale up in size with a proportionally larger Kuiper Belt feature and scaled-up planet orbits. For example, the "frost line" in our solar system — the distance where ices and other volatile elements will not evaporate — is roughly at 500 million miles from the sun. But for hotter Fomalhaut, the frost line is at roughly 1.9 billion miles from the star.

Fomalhaut is burning hydrogen at such a furious rate through nuclear fusion that it will burn out in only 1 billion years, which is 1/10th the lifespan of our sun. This means there is little opportunity for advanced life to evolve on any habitable worlds the star might possess.

Future observations will attempt to see the planet in infrared light and will look for evidence of water vapor clouds in the atmosphere. This would yield clues to the evolution of a comparatively newborn 100-million-year-old planet. Astrometric measurements of the planet's orbit will provide enough precision to yield an accurate mass.

NASA's James Webb Space Telescope, scheduled to launch in 2013, will be able to make coronagraphic observations of Fomalhaut in the near- and mid-infrared. JWST will be able to hunt for other planets in the system and probe the region interior to the dust ring for structures such as an inner asteroid belt.

The science team members are: P. Kalas, J. Graham, E. Chiang, and E. Kite (University of California, Berkeley), M. Clampin (NASA Goddard Space Flight Center, Greenbelt, Md.), M. Fitzgerald (Lawrence Livermore National Laboratory, Livermore, Calif.), and K. Stapelfeldt and J. Krist (NASA Jet Propulsion Laboratory, Pasadena, Calif.).

CONTACT:
J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov

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

A Bubble in Cygnus

Image Credit & Copyright: Keith Quattrocchi, Mel Helm

Adrift in the rich star fields of the constellation Cygnus, this lovely, symmetric bubble nebula was only recently recognized and may not yet appear in astronomical catalogs.

In fact, amateur astronomer Dave Jurasevich identified it as a nebula on July 6 in his images of the complex Cygnus region that included the Crescent Nebula (NGC 6888). He subsequently notified the International Astronomical Union.

Only eleven days later the same object was independently identified by Mel Helm at Sierra Remote Observatories, imaged by Keith Quattrocchi and Helm, and also submitted to the IAU as a potentially unknown nebula.

Their final composite image is seen here, including narrow-band image data that highlights the nebula's delicate outlines. What is the newly recognized bubble nebula? Like the Crescent Nebula itself, this cosmic bubble could be blown by winds from a massive Wolf-Rayet star, or it could be a spherically-shaped planetary nebula, a final phase in the life of a sun-like star.

Wednesday, November 12, 2008

Cassini Finds Mysterious New Aurora on Saturn

Saturn's Polar Aurora
Credit: NASA/JPL/University of Arizona

This image of the northern polar region of Saturn shows both the aurora and underlying atmosphere, seen at two different wavelengths of infrared light as captured by NASA's Cassini spacecraft.

Energetic particles, crashing into the upper atmosphere cause the aurora, shown in blue, to glow brightly at 4 microns (six times the wavelength visible to the human eye). The image shows both a bright ring, as seen from Earth, as well as an example of bright auroral emission within the polar cap that had been undetected until the advent of Cassini. This aurora, which defies past predictions of what was expected, has been observed to grow even brighter than is shown here. Silhouetted by the glow (cast here to the color red) of the hot interior of Saturn (clearly seen at a wavelength of 5 microns, or seven times the wavelength visible to the human eye) are the clouds and haze that underlie this auroral region. For a similar view of the region beneath the aurora see Saturn's North Pole Hexagon and Aurora.

This image is a composite captured with Cassini's visual and infrared mapping spectrometer.

The aurora image was taken in the near-infrared on Nov. 10, 2006, from a distance of 1,061,000 kilometers (659,000 miles), with a phase angle of 157 degrees and a sub-spacecraft planetocentric latitude of 52 degrees north. The image of the clouds was obtained by Cassini on June 15, 2008, from a distance of 602,000 kilometers (374,000 miles) and a sub-spacecraft planetocentric latitude of 73 degrees north.

Saturn has its own unique brand of aurora that lights up the polar cap, unlike any other planetary aurora known in our solar system. This odd aurora revealed itself to one of the infrared instruments on NASA's Cassini spacecraft.

"We've never seen an aurora like this elsewhere," said Tom Stallard, a scientist working with Cassini data at the University of Leicester, England. Stallard is lead author of a paper that appears in the Nov. 13 issue of the journal Nature. "It's not just a ring of auroras like those we've seen at Jupiter or Earth. This aurora covers an enormous area across the pole. Our current ideas on what forms Saturn's aurora predict that this region should be empty, so finding such a bright aurora here is a fantastic surprise."

The new views are available online at: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

Auroras are caused by charged particles streaming along the magnetic field lines of a planet into its atmosphere. Particles from the sun cause Earth's auroras. Many, but not all, of the auroras at Jupiter and Saturn are caused by particles trapped within the magnetic environments of those planets.

Jupiter's main auroral ring, caused by interactions internal to Jupiter's magnetic environment, is constant in size. Saturn's main aurora, which is caused by the solar wind, changes size dramatically as the wind varies. The newly observed aurora at Saturn, however, doesn't fit into either category.

"Saturn's unique auroral features are telling us there is something special and unforeseen about this planet's magnetosphere and the way it interacts with the solar wind and the planet's atmosphere," said Nick Achilleos, Cassini scientist on the Cassini magnetometer team at the University College London. "Trying to explain its origin will no doubt lead us to physics which uniquely operates in the environment of Saturn."

The new infrared aurora appears in a region hidden from NASA's Hubble Space Telescope, which has provided views of Saturn's ultraviolet aurora. Cassini observed it when the spacecraft flew near Saturn's polar region. In infrared light, the aurora sometimes fills the region from around 82 degrees north all the way over the pole. This new aurora is also constantly changing, even disappearing within a 45 minute-period.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson.

Contacts:
Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
Carolina.Martinez@jpl.nasa.gov

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov/home/index.cfm. The visual and infrared mapping spectrometer team homepage is at http://wwwvims.lpl.arizona.edu.

APEX reveals glowing stellar nurseries

Glowing stellar nurseries.
ESO PR Photo 40/08
Credit: ESO/APEX/DSS2/SuperCosmos

Illustrating the power of submillimetre-wavelength astronomy, an APEX image reveals how an expanding bubble of ionised gas about ten light-years across is causing the surrounding material to collapse into dense clumps that are the birthplaces of new stars. Submillimetre light is the key to revealing some of the coldest material in the Universe, such as these cold, dense clouds.

The region, called RCW120, is about 4200 light years from Earth, towards the constellation of Scorpius. A hot, massive star in its centre is emitting huge amounts of ultraviolet radiation, which ionises the surrounding gas, stripping the electrons from hydrogen atoms and producing the characteristic red glow of so-called H-alpha emission.

As this ionised region expands into space, the associated shock wave sweeps up a layer of the surrounding cold interstellar gas and cosmic dust. This layer becomes unstable and collapses under its own gravity into dense clumps, forming cold, dense clouds of hydrogen where new stars are born. However, as the clouds are still very cold, with temperatures of around -250˚ Celsius, their faint heat glow can only be seen at submillimetre wavelengths. Submillimetre light is therefore vital in studying the earliest stages of the birth and life of stars.

The submillimetre-wavelength data were taken with the LABOCA camera on the 12-m Atacama Pathfinder Experiment (APEX) telescope, located on the 5000 m high plateau of Chajnantor in the Chilean Atacama desert. Thanks to LABOCA's high sensitivity, astronomers were able to detect clumps of cold gas four times fainter than previously possible. Since the brightness of the clumps is a measure of their mass, this also means that astronomers can now study the formation of less massive stars than they could before.

The plateau of Chajnantor is also where ESO, together with international partners, is building a next generation submillimetre telescope, ALMA, the Atacama Large Millimeter/submillimeter Array. ALMA will use over sixty 12-m antennas, linked together over distances of more than 16 km, to form a single, giant telescope.

APEX is a collaboration between the Max-Planck-Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. The telescope is based on a prototype antenna constructed for the ALMA project. Operation of APEX at Chajnantor is entrusted to ESO.

Contact
Douglas Pierce-Price
ESO ALMA/APEX Public Information Officer

ESO, Garching, Germany

Phone: +49 89 3200 6759
E-mail: dpiercep (at) eso.org

Dusty Shock Waves Generate Planet Ingredients

Quartz-like Crystals Found in Planetary Disks
Credit: NASA/JPL-Caltech

Shock waves around dusty, young stars might be creating the raw materials for planets, according to new observations from NASA's Spitzer Space Telescope.

The evidence comes in the form of tiny crystals. Spitzer detected crystals similar in make-up to quartz around young stars just beginning to form planets. The crystals, called cristobalite and tridymite, are known to reside in comets, in volcanic lava flows on Earth, and in some meteorites that land on Earth.

Astronomers already knew that crystallized dust grains stick together to form larger particles, which later lump together to form planets. But they were surprised to find cristobalite and tridymite crystals. What's so special about these particular crystals? They require flash heating events, such as shock waves, to form.

The findings suggest that the same kinds of shock waves that cause sonic booms from speeding jets are responsible for creating the stuff of planets throughout the universe.

"By studying these other star systems, we can learn about the very beginnings of our own planets 4.6 billion years ago," said William Forrest of the University of Rochester, N.Y. "Spitzer has given us a better idea of how the raw materials of planets are produced very early on." Forrest and University of Rochester graduate student Ben Sargent led the research, to appear in the Astrophysical Journal.

Planets are born out of swirling pancake-like disks of dust and gas that surround young stars. They start out as mere grains of dust swimming around in a disk of gas and dust, before lumping together to form full-fledged planets. During the early stages of planet development, the dust grains crystallize and adhere together, while the disk itself starts to settle and flatten. This occurs in the first millions of years of a star's life.

When Forrest and his colleagues used Spitzer to examine five young planet-forming disks about 400 light-years away, they detected the signature of silica crystals. Silica is made of only silicon and oxygen and is the main ingredient in glass. When melted and crystallized, it can make the large hexagonal quartz crystals often sold as mystical tokens. When heated to even higher temperatures, it can also form small crystals like those commonly found around volcanoes.

It is this high-temperature form of silica crystals, specifically cristobalite and tridymite, that Forrest's team found in planet-forming disks around other stars for the first time. "Cristobalite and tridymite are essentially high-temperature forms of quartz," said Sargent. "If you heat quartz crystals, you'll get these compounds."

In fact, the crystals require temperatures as high as 1,220 Kelvin (about 1,740 degrees Fahrenheit) to form. But young planet-forming disks are only about 100 to 1,000 Kelvin (about minus 280 degrees Fahrenheit to 1,340 Fahrenheit) -- too cold to make the crystals. Because the crystals require heating followed by rapid cooling to form, astronomers theorized that shock waves could be the cause.

Shock waves, or supersonic waves of pressure, are thought to be created in planet-forming disks when clouds of gas swirling around at high speeds collide. Some theorists think that shock waves might also accompany the formation of giant planets.

The findings are in agreement with local evidence from our own solar system. Spherical pebbles, called chondrules, found in ancient meteorites that fell to Earth are also thought to have been crystallized by shock waves in our solar system's young planet-forming disk. In addition, NASA's Stardust mission found tridymite minerals in comet Wild 2.

Other authors of the paper include C. Tayrien, M.K. McClure, A.R. Basu, P. Mano, Dan Watson, C.J. Bohac, K.H. Kim and J.D. Green of the University of Rochester; A Li of the University of Missouri, Columbia; E. Furlan of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and G.C. Sloan of Cornell University, Ithaca, N.Y.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared spectrograph, which made the observations, was built by Cornell University, Ithaca, N.Y. Its development was led by Jim Houck of Cornell.

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

Monday, November 10, 2008

Our Galaxy's Central Molecular Zone

Credit: A. Ginsburg (U. Colorado - Boulder) et al.,
BGPS Team, GLIMPSE II Team

The central region of our Milky Way Galaxy is a mysterious and complex place. Pictured here in radio and infrared light, the galaxy's central square degree is highlighted in fine detail. The region is known as the Central Molecular Zone.

While much of the extended emission is due to dense gas laced with molecules, also seen are emission nebulas lit up by massive young stars, glowing supernova remnants, and the curving Galactic Center Radio Arc in purple. T

he identity and root cause for many other features remains unknown. Besides a massive black hole named Sgr A*, the Galactic Center houses the galaxy's most active star forming region. This image is not just interesting scientifically. It's esthetic beauty won first prize this year in the AUI/NRAO Image Contest.