Thursday, June 30, 2011

NASA's Spitzer Finds Distant Galaxies Grazed on Gas

This split view shows how a normal spiral galaxy around our local universe (left) might have looked back in the distant universe, when astronomers think galaxies would have been filled with larger populations of hot, bright stars (right). Image credit: NASA/JPL-Caltech/STScI. Full image and caption

PASADENA, Calif. -- Galaxies once thought of as voracious tigers are more like grazing cows, according to a new study using NASA's Spitzer Space Telescope.

Astronomers have discovered that galaxies in the distant, early universe continuously ingested their star-making fuel over long periods of time. This goes against previous theories that the galaxies devoured their fuel in quick bursts after run-ins with other galaxies.

"Our study shows the merging of massive galaxies was not the dominant method of galaxy growth in the distant universe," said Ranga-Ram Chary of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena, Calif. "We're finding this type of galactic cannibalism was rare. Instead, we are seeing evidence for a mechanism of galaxy growth in which a typical galaxy fed itself through a steady stream of gas, making stars at a much faster rate than previously thought."

Chary is the principal investigator of the research, appearing in the Aug. 1 issue of the Astrophysical Journal. According to his findings, these grazing galaxies fed steadily over periods of hundreds of millions of years and created an unusual amount of plump stars, up to 100 times the mass of our sun.

"This is the first time that we have identified galaxies that supersized themselves by grazing," said Hyunjin Shim, also of the Spitzer Science Center and lead author of the paper. "They have many more massive stars than our Milky Way galaxy."

Galaxies like our Milky Way are giant collections of stars, gas and dust. They grow in size by feeding off gas and converting it to new stars. A long-standing question in astronomy is: Where did distant galaxies that formed billions of years ago acquire this stellar fuel? The most favored theory was that galaxies grew by merging with other galaxies, feeding off gas stirred up in the collisions.

Chary and his team addressed this question by using Spitzer to survey more than 70 remote galaxies that existed 1 to 2 billion years after the Big Bang (our universe is approximately 13.7 billion years old). To their surprise, these galaxies were blazing with what is called H alpha, which is radiation from hydrogen gas that has been hit with ultraviolet light from stars. High levels of H alpha indicate stars are forming vigorously. Seventy percent of the surveyed galaxies show strong signs of H alpha. By contrast, only 0.1 percent of galaxies in our local universe possess this signature.

Previous studies using ultraviolet-light telescopes found about six times less star formation than Spitzer, which sees infrared light. Scientists think this may be due to large amounts of obscuring dust, through which infrared light can sneak. Spitzer opened a new window onto the galaxies by taking very long-exposure infrared images of a patch of sky called the GOODS fields, for Great Observatories Origins Deep Survey.

Further analyses showed that these galaxies furiously formed stars up to 100 times faster than the current star-formation rate of our Milky Way. What's more, the star formation took place over a long period of time, hundreds of millions of years. This tells astronomers that the galaxies did not grow due to mergers, or collisions, which happen on shorter timescales. While such smash-ups are common in the universe -- for example, our Milky Way will merge with the Andromeda galaxy in about 5 billion years -- the new study shows that large mergers were not the main cause of galaxy growth. Instead, the results show that distant, giant galaxies bulked up by feeding off a steady supply of gas that probably streamed in from filaments of dark matter.

Chary said, "If you could visit a planet in one of these galaxies, the sky would be a crazy place, with tons of bright stars, and fairly frequent supernova explosions."

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the Spitzer Space Telescope mission for the agency's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at Caltech. Caltech manages JPL for NASA.

For more information about Spitzer, visit http://www.nasa.gov/spitzer and http://spitzer.caltech.edu/ .

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

Trent Perrotto 202-358-0321
Headquarters, Washington
trent.j.perrotto@nasa.gov

Integral challenges physics beyond Einstein

December 2004 that Philippe Laurent and colleagues have now analysed in detail. It was so bright that Integral could also measure its polarisation, allowing Laurent and colleagues to look for differences in the signal from different energies. The GRB shown here, on 25 November 2002, was the first captured using such a powerful gamma-ray camera as Integral’s. When they occur, GRBs shine as brightly as hundreds of galaxies each containing billions of stars. Credits: ESA/SPI Team/ECF

ESA’s Integral gamma-ray observatory has provided results that will dramatically affect the search for physics beyond Einstein. It has shown that any underlying quantum ‘graininess’ of space must be at much smaller scales than previously predicted.

Einstein’s General Theory of Relativity describes the properties of gravity and assumes that space is a smooth, continuous fabric. Yet quantum theory suggests that space should be grainy at the smallest scales, like sand on a beach.

One of the great concerns of modern physics is to marry these two concepts into a single theory of quantum gravity.

Now, Integral has placed stringent new limits on the size of these quantum ‘grains’ in space, showing them to be much smaller than some quantum gravity ideas would suggest.

According to calculations, the tiny grains would affect the way that gamma rays travel through space. The grains should ‘twist’ the light rays, changing the direction in which they oscillate, a property called polarisation.

High-energy gamma rays should be twisted more than the lower energy ones, and the difference in the polarisation can be used to estimate the size of the grains.

Philippe Laurent of CEA Saclay and his collaborators used data from Integral’s IBIS instrument to search for the difference in polarisation between high- and low-energy gamma rays emitted during one of the most powerful gamma-ray bursts (GRBs) ever seen.

GRBs come from some of the most energetic explosions known in the Universe. Most are thought to occur when very massive stars collapse into neutron stars or black holes during a supernova, leading to a huge pulse of gamma rays lasting just seconds or minutes, but briefly outshining entire galaxies.

GRB 041219A took place on 19 December 2004 and was immediately recognised as being in the top 1% of GRBs for brightness. It was so bright that Integral was able to measure the polarisation of its gamma rays accurately.

Dr Laurent and colleagues searched for differences in the polarisation at different energies, but found none to the accuracy limits of the data.

Some theories suggest that the quantum nature of space should manifest itself at the ‘Planck scale’: the minuscule 10-35 of a metre, where a millimetre is 10-3 m.

However, Integral’s observations are about 10 000 times more accurate than any previous and show that any quantum graininess must be at a level of 10-48 m or smaller.

“This is a very important result in fundamental physics and will rule out some string theories and quantum loop gravity theories,” says Dr Laurent.

Integral made a similar observation in 2006, when it detected polarised emission from the Crab Nebula, the remnant of a supernova explosion just 6500 light years from Earth in our own galaxy.

This new observation is much more stringent, however, because GRB 041219A was at a distance estimated to be at least 300 million light years.

In principle, the tiny twisting effect due to the quantum grains should have accumulated over the very large distance into a detectable signal. Because nothing was seen, the grains must be even smaller than previously suspected.

“Fundamental physics is a less obvious application for the gamma-ray observatory, Integral,” notes Christoph Winkler, ESA’s Integral Project Scientist. “Nevertheless, it has allowed us to take a big step forward in investigating the nature of space itself.”

Now it’s over to the theoreticians, who must re-examine their theories in the light of this new result.

Contact for further information

Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Email: markus.bauer@esa.int
Tel: +31 71 565 6799
Mob: +31 61 594 3 954

Dr Philippe Laurent
Laboratoire APC, CEA/IRFU
Email: philippe.laurent@cea.fr
Tel: +33 1 69 08 80 66 or +33 1 57 27 60 72

Dr Christoph Winkler
ESA Integral Project Scientist
Email: christoph.winkler@rssd.esa.int
Tel: +31 71 5653591

Notes for editors

Constraints on Lorentz Invariance Violation using INTEGRAL/IBIS observations of GRB041219A by P. Laurent, D. Götz, P. Binetruy, S. Covino, A. Fernandez-Soto is published online at Physical Review D June, 28th 2011, Vol. 83, issue 12.

Wednesday, June 29, 2011

Making a Spectacle of Star Formation in Orion

Best known as Messier 78, the two round greenish nebulae are actually cavities carved out of the surrounding dark dust clouds. Image credit: NASA/JPL-Caltech. Full image and caption

Looking like a pair of eyeglasses only a rock star would wear, this nebula brings into focus a murky region of star formation. NASA's Spitzer Space Telescope exposes the depths of this dusty nebula with its infrared vision, showing stellar infants that are lost behind dark clouds when viewed in visible light.

Best known as Messier 78, the two round greenish nebulae are actually cavities carved out of the surrounding dark dust clouds. The extended dust is mostly dark, even to Spitzer's view, but the edges show up in mid-wavelength infrared light as glowing, red frames surrounding the bright interiors. Messier 78 is easily seen in small telescopes in the constellation of Orion, just to the northeast of Orion's belt, but looks strikingly different, with dominant, dark swaths of dust. Spitzer's infrared eyes penetrate this dust, revealing the glowing interior of the nebulae.

The light from young, newborn stars are starting to carve out cavities within the dust, and eventually, this will become a larger nebula like the "green ring" imaged by Spitzer (see http://www.jpl.nasa.gov/news/news.cfm?release=2011-183).

A string of baby stars that have yet to burn their way through their natal shells can be seen as red pinpoints on the outside of the nebula. Eventually these will blossom into their own glowing balls, turning this two-eyed eyeglass into a many-eyed monster of a nebula.

This is a three-color composite that shows infrared observations from two Spitzer instruments. Blue represents 3.6- and 4.5-micron light, and green shows light of 5.8 and 8 microns, both captured by Spitzer's infrared array camera. Red is 24-micron light detected by Spitzer's multiband imaging photometer.

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

Most Distant Quasar Found

PR Image eso1122a
An artist’s rendering of the most distant quasar

PR Image eso1122b
The most distant quasar

PR Image eso1122c
Wide-field view of the sky around the most remote quasar

PR Video eso1122a
ESOcast 32: Most Distant Quasar Found

PR Video eso1122b
Zooming in on the most distant quasar found so far

PR Video eso1122c
A 3D animation of the most distant quasar

A team of European astronomers has used ESO’s Very Large Telescope and a host of other telescopes to discover and study the most distant quasar found to date. This brilliant beacon, powered by a black hole with a mass two billion times that of the Sun, is by far the brightest object yet discovered in the early Universe. The results will appear in the 30 June 2011 issue of the journal Nature.

“This quasar is a vital probe of the early Universe. It is a very rare object that will help us to understand how supermassive black holes grew a few hundred million years after the Big Bang,” says Stephen Warren, the study’s team leader.

Quasars are very bright, distant galaxies that are believed to be powered by supermassive black holes at their centres. Their brilliance makes them powerful beacons that may help to probe the era when the first stars and galaxies were forming. The newly discovered quasar is so far away that its light probes the last part of the reionisation era [1].

The quasar that has just been found, named ULAS J1120+0641 [2], is seen as it was only 770 million years after the Big Bang (redshift 7.1, [3]). It took 12.9 billion years for its light to reach us.

Although more distant objects have been confirmed (such as a gamma-ray burst at redshift 8.2, eso0917, and a galaxy at redshift 8.6, eso1041), the newly discovered quasar is hundreds of times brighter than these. Amongst objects bright enough to be studied in detail, this is the most distant by a large margin.

The next most-distant quasar is seen as it was 870 million years after the Big Bang (redshift 6.4). Similar objects further away cannot be found in visible-light surveys because their light, stretched by the expansion of the Universe, falls mostly in the infrared part of the spectrum by the time it gets to Earth. The European UKIRT Infrared Deep Sky Survey (UKIDSS) which uses the UK's dedicated infrared telescope [4] in Hawaii was designed to solve this problem. The team of astronomers hunted through millions of objects in the UKIDSS database to find those that could be the long-sought distant quasars, and eventually struck gold.

“It took us five years to find this object,” explains Bram Venemans, one of the authors of the study. “We were looking for a quasar with redshift higher than 6.5. Finding one that is this far away, at a redshift higher than 7, was an exciting surprise. By peering deep into the reionisation era, this quasar provides a unique opportunity to explore a 100-million-year window in the history of the cosmos that was previously out of reach.”

The distance to the quasar was determined from observations made with the FORS2 instrument on ESO’s Very Large Telescope (VLT) and instruments on the Gemini North Telescope [5]. Because the object is comparatively bright it is possible to take a spectrum of it (which involves splitting the light from the object into its component colours). This technique allowed the astronomers to find out quite a lot about the quasar.

These observations showed that the mass of the black hole at the centre of ULAS J1120+0641 is about two billion times that of the Sun. This very high mass is hard to explain so early on after the Big Bang. Current theories for the growth of supermassive black holes predict a slow build-up in mass as the compact object pulls in matter from its surroundings.

“We think there are only about 100 bright quasars with redshift higher than 7 over the whole sky,” concludes Daniel Mortlock, the leading author of the paper. “Finding this object required a painstaking search, but it was worth the effort to be able to unravel some of the mysteries of the early Universe.”

Notes

[1] About 300 000 years after the Big Bang, which occurred 13.7 billion years ago, the Universe had cooled down enough to allow electrons and protons to combine into neutral hydrogen (a gas without electric charge). This cool dark gas permeated the Universe until the first stars started forming about 100 to 150 million years later. Their intense ultraviolet radiation slowly split the hydrogen atoms back into protons and electrons, a process called reionisation, making the Universe more transparent to ultraviolet light. It is believe that this era occurred between about 150 million to 800 million years after the Big Bang.

[2] The object was found using data from the UKIDSS Large Area Survey, or ULAS. The numbers and prefix ‘J’ refer to the quasar’s position in the sky.

[3] Because light travels at a finite speed, astronomers look back in time as they look further away into the Universe. It took 12.9 billion years for the light from ULAS J1120+0641 to travel to telescopes on Earth so the quasar is seen as it was when the Universe was only 770 million years old. In those 12.9 billion years, the Universe expanded and the light from the object stretched as a result. The cosmological redshift, or simply redshift, is a measure of the total stretching the Universe underwent between the moment when the light was emitted and the time when it was received.

[4] UKIRT is the United Kingdom Infrared Telescope. It is owned by the UK’s Science and Technology Facilities Council and operated by the staff of the Joint Astronomy Centre in Hilo, Hawaii.

[5] FORS2 is the VLT’s FOcal Reducer and low dispersion Spectrograph. Other instruments used to split up the light of the object were the Gemini Multi-Object Spectrograph (GMOS) and the Gemini Near-Infrared Spectrograph (GNIRS). The Liverpool Telescope, the Isaac Newton Telescope and the UK Infrared Telescope (UKIRT) were also used to confirm survey measurements.

More information

This research was presented in a paper to appear in the journal Nature on 30 June 2011.

The team is composed of Daniel J. Mortlock (Imperial College London [Imperial], UK), Stephen J. Warren (Imperial), Bram P. Venemans (ESO, Garching, Germany), Mitesh Patel (Imperial), Paul C. Hewett (Institute of Astronomy [IoA], Cambridge, UK), Richard G. McMahon (IoA), Chris Simpson (Liverpool John Moores University, UK), Tom Theuns (Institute for Computational Cosmology, Durham, UK and University of Antwerp, Belgium), Eduardo A. Gonzáles-Solares (IoA), Andy Adamson (Joint Astronomy Centre, Hilo, USA), Simon Dye (Centre for Astronomy and Particle Theory, Nottingham, UK), Nigel C. Hambly (Institute for Astronomy, Edinburgh, UK), Paul Hirst (Gemini Observatory, Hilo, USA), Mike J. Irwin (IoA), Ernst Kuiper (Leiden Observatory, The Netherlands), Andy Lawrence (Institute for Astronomy, Edinburgh, UK), Huub J. A. Röttgering (Leiden Observatory, The Netherlands).

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

Links
Research paper: Nature paper
Photos of the VLT

Contacts

Daniel Mortlock
Astrophysics Group, Blackett Laboratory, Imperial College London
London, United Kingdom
Tel: +44 20 7594 7878
Email: d.mortlock@imperial.ac.uk

Bram Venemans
ESO Astronomer
Garching bei München, Germany
Tel: +49 89 3200 6631
Email: bveneman@eso.org

Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: rhook@eso.org

Tuesday, June 28, 2011

Neutron star bites off more than it can chew

HI-RES GIF (Size: 10 261 kb)
This animated sequence of images illustrates the partial ingestion of a clump of matter by the neutron star hosted in the Supergiant Fast X-Ray Transient, IGR J18410-0535.

The ingestion of the clump material produced a dramatic increase in the X-rays released by the neutron star, which was detected with XMM-Newton. The peak in the X-ray luminosity corresponds to the period when the accretion rate was at its maximum.

Credits: ESA/AOES Medialab
ESA’s XMM-Newton space observatory has watched a faint star flare up at X-ray wavelengths to almost 10 000 times its normal brightness. Astronomers believe the outburst was caused by the star trying to eat a giant clump of matter.

The flare took place on a neutron star, the collapsed heart of a once much larger star. Now about 10 km in diameter, the neutron star is so dense that it generates a strong gravitational field.

The clump of matter was much larger than the neutron star and came from its enormous blue supergiant companion star.

“This was a huge bullet of gas that the star shot out, and it hit the neutron star allowing us to see it,” says Enrico Bozzo, ISDC Data Centre for Astrophysics, University of Geneva, Switzerland, and team leader of this research.

The flare lasted four hours and the X-rays came from the gas in the clump as it was heated to millions of degrees while being pulled into the neutron star’s intense gravity field. In fact, the clump was so big that not much of it hit the neutron star. Yet, if the neutron star had not been in its path, this clump would probably have disappeared into space without trace.

XMM-Newton caught the flare during a scheduled 12.5-hour observation of the system, which is known only by its catalogue number IGR J18410-0535, but the astronomers were unaware of their catch immediately.

The telescope works through a sequence of observations carefully planned to make the best use of the space observatory’s time, then sends the data to Earth.

It was about ten days after the observation that Dr Bozzo and his colleagues received the data and quickly realised they had something special. Not only were they pointing in the right direction to see the flare, but the observation had lasted long enough for them to see it from beginning to end.

“I don’t know if there is any way to measure luck, but we were extremely lucky,” says Dr Bozzo. He estimates that an X-ray flare of this magnitude can be expected a few times a year at the most for this particular star system.

The duration of the flare allowed them to estimate the size of the clump. It was much larger than the star, probably 16 million km across, or about 100 billion times the volume of the Moon. Yet, according to the estimate made from the flare’s brightness, the clump contained only one-thousandth of our natural satellite’s mass.

These figures will help astronomers understand the behaviour of the blue supergiant and the way it emits matter into space. All stars expel atoms into space, creating a stellar wind. The X-ray flare shows that this particular blue supergiant does it in a clumpy fashion, and the estimated size and mass of the cloud allow constraints to be placed on the process.

“This remarkable result highlights XMM-Newton's unique capabilities,” comments Norbert Schartel, XMM-Newton Project Scientist. “Its observations indicate that these flares can be linked to the neutron star attempting to ingest a giant clump of matter.”


Contact for further information


Markus Bauer

ESA Science and Robotic Exploration Communication Officer
Email: markus.bauer@esa.int
Tel: +31 71 565 6799
Mob: +31 61 594 3 954

Enrico Bozzo
ISDC Data Centre for Astrophysics
University of Geneva, Switzerland
Tel: +41 22 37 92158
Email: enrico.bozzo@unige.ch

Norbert Schartel
ESA XMM-Newton Project Scientist
Tel: +34 91 8131 184
Email: norbert.schartel@esa.int

Notes to editors

IGR J18410-0535 belongs to the class of star called Supergiant Fast X-Ray Transients, which were discovered by ESA’s INTEGRAL spacecraft in 2005.

Bozzo, E., et al., “XMM-Newton observations of IGR J18410-0535: the ingestion of a clump by a supergiant fast X-ray transient”, will be published in a forthcoming edition of Astronomy and Astrophysics.

Monday, June 27, 2011

Engulfed by Stars Near the Milky Way’s Heart

The globular star cluster Djorgovski 1
Credit: ESA/Hubble & NASA

The NASA/ESA Hubble Space Telescope has imaged an area so jam-packed with stars that they almost overwhelm the inky blackness of space. This includes the globular star cluster Djorgovski 1, which was only discovered in 1987

Djorgovski 1 is located close to the centre of our Milky Way Galaxy, within the bulge. If the galaxy is thought of as being like a city, then this bulge is the very busiest district at its centre. Djorgovski 1's proximity to this hub — within just a few degrees — explains why the picture is teeming with stars.

Globular clusters like Djorgovski 1 formed early in the Milky Way's history, and as such may hold clues about the inner galaxy’s early evolution. However, with so much material in the way, obtaining accurate data is problematic. To make matters worse, these stars are faint. Even the most luminous stars in Djorgovski 1 are fainter than the brightest giant stars in the bulge.

Another quandary is apparent: how do you know which stars belong to Djorgovski 1, and which are from the bulge? To determine this, astronomers have studied the chemical composition of numerous stars in the area. Stars with a similar composition likely belong in the same group, like siblings in a family. This technique has successfully provided the information to distinguish between stars in Djorgovski 1 and the surrounding bulge.

These studies also reveal that Djorgovski 1’s stars contain hydrogen and helium, but not much else. In astronomical terms, they are described as “metal-poor”. In fact, it appears that Djorgovski 1 is one of the most metal-poor clusters in the inner galaxy. It is not clear why this is the case, but additional research may shed light on the issue.

This picture was created from multiple images taken with the Wide Field Camera of Hubble’s Advanced Camera for Surveys. Exposures through a yellow/orange filter (F606W) are coloured blue and images through a near-infrared filter (F814W) are shown as red. The total exposure times per filter are 340 s and 360 s, respectively, and the field of view is 2.7 by 1.5 arcminutes in extent.

Thursday, June 23, 2011

The Flames of Betelgeuse

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The flames of Betelgeuse

PR Image eso1121b
The star Betelgeuse in the constellation of Orion

PR Video eso1121a
Zooming in on the flames of Betelgeuse

Using the VISIR instrument on ESO’s Very Large Telescope (VLT), astronomers have imaged a complex and bright nebula around the supergiant star Betelgeuse in greater detail than ever before. This structure, which resembles flames emanating from the star, is formed as the behemoth sheds its material into space.

Betelgeuse, a red supergiant in the constellation of Orion, is one of the brightest stars in the night sky. It is also one of the biggest, being almost the size of the orbit of Jupiter — about four and half times the diameter of the Earth’s orbit. The VLT image shows the surrounding nebula, which is much bigger than the supergiant itself, stretching 60 billion kilometres away from the star's surface — about 400 times the distance of the Earth from the Sun.

Red supergiants like Betelgeuse represent one of the last stages in the life of a massive star. In this short-lived phase, the star increases in size, and expels material into space at a tremendous rate — it sheds immense quantities of material (about the mass of the Sun) in just 10 000 years.

The process by which material is shed from a star like Betelgeuse involves two phenomena. The first is the formation of huge plumes of gas (although much smaller than the nebula now imaged) extending into space from the star’s surface, previously detected using the NACO instrument on the VLT [1]. The other, which is behind the ejection of the plumes, is the vigorous up and down movement of giant bubbles in Betelgeuse’s atmosphere — like boiling water circulating in a pot (eso0927).

The new results show that the plumes seen close to the star are probably connected to structures in the outer nebula now imaged in the infrared with VISIR. The nebula cannot be seen in visible light, as the very bright Betelgeuse completely outshines it. The irregular, asymmetric shape of the material indicates that the star did not eject its material in a symmetric way. The bubbles of stellar material and the giant plumes they originate may be responsible for the clumpy look of the nebula.

The material visible in the new image is most likely made of silicate and alumina dust. This is the same material that forms most of the crust of the Earth and other rocky planets. At some time in the distant past, the silicates of the Earth were formed by a massive (and now extinct) star similar to Betelgeuse.

In this composite image, the earlier NACO observations of the plumes are reproduced in the central disc. The small red circle in the middle has a diameter about four and half times that of the Earth’s orbit and represents the location of Betelgeuse’s visible surface. The black disc corresponds to a very bright part of the image that was masked to allow the fainter nebula to be seen. The VISIR images were taken through infrared filters sensitive to radiation of different wavelengths, with blue corresponding to shorter wavelengths and red to longer. The field of view is 5.63 x 5.63 arcseconds.

Notes

[1] NACO is a VLT instrument that combines the Nasmyth Adaptive Optics System (NAOS) and the Near-infrared Imager and Spectrograph (CONICA). It provides adaptive optics assisted imaging, imaging polarimetry, coronography and spectroscopy, at near-infrared wavelengths.

More information

This research was presented in a paper to appear in the journal Astronomy & Astrophysics.

The team is composed of P. Kervella (Observatoire de Paris, France), G. Perrin (Observatoire de Paris, France), A. Chiavassa (Université Libre de Bruxelles, Belgium), S. T. Ridgway (National Optical Astronomy Observatories, Tucson, USA), J. Cami (University of Western Ontario,Canada; SETI Institute, Mountain View, USA), X. Haubois (Universidade de São Paulo, Brazil) and T. Verhoelst (Instituut voor Sterrenkunde, Leuven, Belgium).

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

Links
Research paper (Astronomy & Astrophysics)
Photos of the VLT

Contacts

Pierre Kervella
LESIA, Observatoire de Paris / CNRS, Université Pierre et Marie Curie
Paris, France
Tel: +33 1 45 07 79 66
Email: Pierre.Kervella@obspm.fr

Guy Perrin
LESIA, Observatoire de Paris / CNRS, Université Pierre et Marie Curie
Paris, France
Tel: +33 1 45 07 79 63
Email: guy.perrin@obspm.fr

Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: rhook@eso.org

Wednesday, June 22, 2011

Cassini Captures Ocean-Like Spray at Saturn Moon

Dramatic plumes, both large and small, spray water ice out from many locations along the famed "tiger stripes" near the south pole of Saturn's moon Enceladus. The tiger stripes are fissures that spray icy particles, water vapor and organic compounds. Image credit: NASA/JPL/Space Science Institute . Full image and caption

PASADENA, Calif. -- NASA's Cassini spacecraft has discovered the best evidence yet for a large-scale saltwater reservoir beneath the icy crust of Saturn's moon Enceladus. The data came from the spacecraft's direct analysis of salt-rich ice grains close to the jets ejected from the moon.

Data from Cassini's cosmic dust analyzer show the grains expelled from fissures, known as tiger stripes, are relatively small and predominantly low in salt far away from the moon. But closer to the moon's surface, Cassini found that relatively large grains rich with sodium and potassium dominate the plumes. The salt-rich particles have an "ocean-like" composition and indicate that most, if not all, of the expelled ice and water vapor comes from the evaporation of liquid salt water. The findings appear in this week's issue of the journal Nature.

"There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than salt water under Enceladus's icy surface," said Frank Postberg, a Cassini team scientist at the University of Heidelberg, Germany, and the lead author on the paper. When water freezes, the salt is squeezed out, leaving pure water ice behind. If the plumes emanated from ice, they should have very little salt in them.

The Cassini mission discovered Enceladus' water-vapor and ice jets in 2005. In 2009, scientists working with the cosmic dust analyzer examined some sodium salts found in ice grains of Saturn's E ring, the outermost ring that gets its material primarily from Enceladean jets. But the link to subsurface salt water was not definitive.

The new paper analyzes three Enceladus flybys in 2008 and 2009 with the same instrument, focusing on the composition of freshly ejected plume grains. The icy particles hit the detector target at speeds between 15,000 and 39,000 mph (23,000 and 63,000 kilometers per hour), vaporizing instantly. Electrical fields inside the cosmic dust analyzer separated the various constituents of the impact cloud.

The data suggest a layer of water between the moon's rocky core and its icy mantle, possibly as deep as about 50 miles (80 kilometers) beneath the surface. As this water washes against the rocks, it dissolves salt compounds and rises through fractures in the overlying ice to form reserves nearer the surface. If the outermost layer cracks open, the decrease in pressure from these reserves to space causes a plume to shoot out. Roughly 400 pounds (200 kilograms) of water vapor is lost every second in the plumes, with smaller amounts being lost as ice grains. The team calculates the water reserves must have large evaporating surfaces, or they would freeze easily and stop the plumes.

"This finding is a crucial new piece of evidence showing that environmental conditions favorable to the emergence of life can be sustained on icy bodies orbiting gas giant planets," said Nicolas Altobelli, the European Space Agency's project scientist for Cassini.

Cassini's ultraviolet imaging spectrograph also recently obtained complementary results that support the presence of a subsurface ocean. A team of Cassini researchers led by Candice Hansen of the Planetary Science Institute in Tucson, Ariz., measured gas shooting out of distinct jets originating in the moon's south polar region at five to eight times the speed of sound, several times faster than previously measured. These observations of distinct jets, from a 2010 flyby, are consistent with results showing a difference in composition of ice grains close to the moon's surface and those that made it out to the E ring. That paper was published in the June 9 issue of Geophysical Research Letters.

"Without an orbiter like Cassini to fly close to Saturn and its moons -- to taste salt and feel the bombardment of ice grains -- scientists would never have known how interesting these outer solar system worlds are," said Linda Spilker, NASA's Cassini project scientist at the Jet Propulsion Laboratory in Pasadena, Calif.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The mission is managed by JPL for NASA's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology, Pasadena.

For more information about Cassini, visit:
http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov

Contacts

Jia-Rui Cook 818-354-0850

Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

Dwayne C. Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown@nasa.gov

Markus Bauer 011-31-71-565-6799
European Space Agency, Noordwijk, the Netherlands
markus.bauer@esa.int

A Galactic Crash Investigation

PR Image eso1120a
X-rays, dark matter and galaxies in the cluster Abell 2744

PR Image eso1120b
Pandora’s Cluster — a galactic crash investigation

PR Image eso1120c
Pandora’s Cluster — the merging galaxy cluster Abell 2744

PR Image eso1120d
Pandora’s Cluster — Hubble view of Abell 2744

PR Image eso1120e
Wide-field view of Abell 2744

PR Video eso1120a
ESOcast 31: Pandora's Cluster

PR Video eso1120b
Simulation of the merging events in Abell 2744

PR Video eso1120c
Zooming in on Pandora’s Cluster

Pan across Abell 2744, Pandora’s Cluster

A team of scientists has studied the galaxy cluster Abell 2744, nicknamed Pandora’s Cluster. They have pieced together the cluster’s complex and violent history using telescopes in space and on the ground, including ESO’s Very Large Telescope and the Hubble Space Telescope. Abell 2744 seems to be the result of a simultaneous pile-up of at least four separate galaxy clusters and this complex collision has produced strange effects that have never been seen together before.

When huge clusters of galaxies crash together, the resulting mess is a treasure trove of information for astronomers. By investigating one of the most complex and unusual colliding clusters in the sky, an international team of astronomers has pieced together the history of a cosmic crash that took place over a period of 350 million years.

Julian Merten, one of the lead scientists for this new study of cluster Abell 2744, explains: “Like a crash investigator piecing together the cause of an accident, we can use observations of these cosmic pile-ups to reconstruct events that happened over a period of hundreds of millions of years. This can reveal how structures form in the Universe, and how different types of matter interact with each other when they are smashed together.”

“We nicknamed it Pandora’s Cluster because so many different and strange phenomena were unleashed by the collision. Some of these phenomena had never been seen before,” adds Renato Dupke, another member of the team.

Abell 2744 has now been studied in more detail than ever before by combining data from ESO’s Very Large Telescope (VLT), the Japanese Subaru telescope, the NASA/ESA Hubble Space Telescope, and NASA’s Chandra X-Ray Observatory.

The galaxies in the cluster are clearly visible in the VLT and Hubble images. Although the galaxies are bright they make up less than 5% of the mass there. The rest is gas (around 20%), which is so hot that it shines only in X-rays, and dark matter (around 75%), which is completely invisible. To understand what was going on in the collision the team needed to map the positions of all three types of matter in Abell 2744.

Dark matter is particularly elusive as it does not emit, absorb or reflect light (hence its name), but only makes itself apparent through its gravitational attraction. To pinpoint the location of this mysterious substance the team exploited a phenomenon known as gravitational lensing. This is the bending of light rays from distant galaxies as they pass through the gravitational fields present in the cluster. The result is a series of telltale distortions in the images of galaxies in the background of the VLT and Hubble observations. By carefully plotting the way that these images are distorted, it is possible to map quite accurately where the hidden mass — and hence the dark matter — actually lies.

By comparison, finding the hot gas in the cluster is simpler as NASA’s Chandra X-ray Observatory can observe it directly. These observations are not just crucial to find out where the gas is, but also to show the angles and speeds at which different components of the cluster came together.

When the astronomers looked at the results they found many curious features. “Abell 2744 seems to have formed from four different clusters involved in a series of collisions over a period of some 350 million years. The complicated and uneven distribution of the different types of matter is extremely unusual and fascinating,” says Dan Coe, the other lead author of the study.

It seems that the complex collision has separated out some of the hot gas and dark matter so that they now lie apart from each other, and from the visible galaxies. Pandora’s Cluster combines several phenomena that have only ever been seen singly in other systems.

Near the core of the cluster is a “bullet”, where the gas of one cluster collided with that of another to create a shock wave. The dark matter passed through the collision unaffected [1].

In another part of the cluster there seem to be galaxies and dark matter, but no hot gas. The gas may have been stripped away during the collision, leaving behind no more than a faint trail.

Even odder features lie in the outer parts of the cluster. One region contains lots of dark matter, but no luminous galaxies or hot gas. A separate ghostly clump of gas has been ejected, which precedes rather than follows the associated dark matter. This puzzling arrangement may be telling astronomers something about how dark matter behaves and how the various ingredients of the Universe interact with each other.

Galaxy clusters are the biggest structures in the cosmos, containing literally trillions of stars. The way they form and develop through repeated collisions has profound implications for our understanding of the Universe. Further studies of the Pandora’s Cluster, the most complex and fascinating merger yet found, are in progress.
Notes

[1] This effect has been seen before in a few galaxy cluster collisions, including the original "Bullet Cluster", 1E 0657-56.

More information

This research is presented in a paper entitled “Creation of cosmic structure in the complex galaxy cluster merger Abell 2744”, to appear in Monthly Notices of the Royal Astronomical Society.

The team is composed of J. Merten (Institute for Theoretical Astrophysics, Heidelberg, Germany; INAF-Osservatorio Astronomico di Bologna, Italy), D. Coe (Space Telescope Science Institute, Baltimore, USA), R. Dupke (University of Michigan, USA; Eureka Scientific, USA; National Observatory, Rio de Janeiro, Brazil), R. Massey (University of Edinburgh, Scotland), A. Zitrin (Tel Aviv University, Israel), E.S. Cypriano (University of Sao Paulo, Brazil), N. Okabe (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan), B. Frye (University of San Francisco, USA), F. Braglia (University of British Columbia, Canada), Y. Jimenez-Teja (Instituto de Astrofisica de Andalucia, Granada, Spain), N. Benitez (Instituto de Astrofisica de Andalucia), T. Broadhurst (University of Basque Country, Spain), J. Rhodes (Jet Propulsion Laboratory/Caltech, USA), M. Meneghetti (INAF-Osservatorio Astronomico di Bologna, Italy), L. A. Moustakas (Caltech), L. Sodre Jr. (University of Sao Paulo, Brazil), J. Krick (Spitzer Science Center/IPAC/Caltech, USA) and J. N. Bregman (University of Michigan).

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

Links
Research paper
Photos of the VLT

Contacts

Julian Merten
Institute for Theoretical Astrophysics
Heidelberg, Germany
Tel: +49 6221 54 8987
Email: jmerten@ita.uni-heidelberg.de

Daniel Coe
Space Telescope Science Institute
Baltimore, USA
Tel: +1 410 338 4312
Email: dcoe@stsci.edu

Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: rhook@eso.org

Oli Usher
Hubble/ESA
Garching, Germany
Tel: +49 89 3200 6855
Email: ousher@eso.org

Tuesday, June 21, 2011

Astronomers Discover That Galaxies Are Either Asleep or Awake

Bluer galaxies are actively “awake” and forming stars, while redder galaxies have shut down and are “asleep.” (Image: NASA, ESA, S. Beckwith (STScI) and the HUDF team)

Astronomers have probed into the distant universe and discovered that galaxies display one of two distinct behaviors: they are either awake or asleep, actively forming stars or are not forming any new stars at all.

Scientists have known for several years that galaxies in the nearby universe seem to fall into one of these two states. But a new survey of the distant universe shows that even very young galaxies as far away as 12 billion light years are either awake or asleep as well, meaning galaxies have behaved this way for more than 85 percent of the history of the universe. (Looking at galaxies farther away is like looking back in time when they were much younger, because of how long it takes the light they emit to reach us here on Earth.)

“The fact that we see such young galaxies in the distant universe that have already shut off is remarkable,” said Kate Whitaker, a Yale University graduate student and lead author of the paper, which is published in the June 20 online edition of the Astrophysical Journal.

In order to determine whether the galaxies were asleep or awake, Whitaker and her colleagues fabricated a new set of filters, each one sensitive to different wavelengths of light, which they used on a 4-meter Kitt Peak telescope in Arizona. They spent 75 nights peering into the distant universe and collecting light from 40,000 galaxies ranging in distance from the nearby universe out to 12 billion light years away. The resulting survey is the deepest and most complete ever made at those distances and wavelengths of light.

The team deciphered the galaxies’ dual behavior based on the color of the light they emit. Because of the physics of star formation, active, wakeful galaxies appear bluer, while the light emitted by passive, sleepy galaxies tends toward the redder end of the spectrum.

The researchers found that there are many more active galaxies than passive ones, which agrees with the current thinking that galaxies start out actively forming stars before eventually shutting down.

“We don’t see many galaxies in the in-between state,” said Pieter van Dokkum, a Yale astronomer and another author of the paper. “This discovery shows how quickly galaxies go from one state to the other, from actively forming stars to shutting off.”

Whether the sleeping galaxies have completely shut down remains an open question, Whitaker said. However, the new study suggests the active galaxies are forming stars at rates about 50 times greater than their sleepy counterparts.

“Next, we hope to determine whether galaxies go back and forth between waking and sleeping or whether they fall asleep and never wake up again,” van Dokkum said. “We’re also interested in how long it takes galaxies to fall asleep, and whether we can catch one in the act of dozing off.”

Other authors of the study include Ivo Labbé (Leiden University and Carnegie Observatories); Gabriel Brammer (Yale University and European Southern Observatory); Mariska Kriek (Princeton University and Harvard-Smithsonian Center for Astrophysics); Danilo Marchesini (Tufts University); Ryan Quadri and Marijn Franx (Leiden University); Adam Muzzin, Rachel Bezanson, Kyoung-Soo Lee, Britt Lundgren, Erica Nelson, Tomer Tal and David Wake (Yale University); Rik Williams (Carnegie Observatories); Garth Illingworth (UCO/Lick Observatory); and Gregory Rudnick (University of Kansas).

The ATLAS3D project: Replacing the handle of Hubble's tuning fork



A team of 25 astronomers from Europe and Northern America, including ASTRON astronomers Morganti, Oosterloo, and Serra, has shown that many galaxies, which are normally classified as spheroid galaxies according to the 70 year old Hubble classification scheme, are in fact spiral galaxies. The so-called ATLAS3D team observed a sample of 260 galaxies with the SAURON spectrograph on the 4.2-meter William Herschel Telescope on La Palma, which allowed them to determine the movements of the stars in these carefully selected galaxies. The results are important because it gives astronomers more information about the way galaxies form.

The team proposed a revised scheme in which the vast majority of spheroid galaxies, also known as early-type galaxies, are close relatives of spiral galaxies and for this reason form a parallel sequence to them. The new paradigm highlights a much closer connection between early-type and spiral galaxies than previously thought, and this will need to be considered in future models of how galaxies form. The above results were presented in three ATLAS3D team papers which will appear this month on the journal Monthly Notices of the Royal Astronomical Society.

Since Edwin Hubble introduced his famous tuning fork diagram more than 70 years ago, spiral galaxies and early-type galaxies have been regarded as being two distinct families. The spirals are characterised by the presence of disks of stars and gas in rapid rotation, while the early-types are gas poor and described as spheroid systems, with less rotation and often non-axisymmetric shapes. This clear distinction is emphasized in Hubble's tuning-fork diagram, where early-type galaxies lie on the handle of the fork, well separated from spiral galaxies. The separation is physically relevant as it implies a distinct path of formation for the two classes of objects.

A known issue of Hubble's classification, however, is that it mostly relies on optical images, from which it is nearly impossible to recognize thin face-on disks of stars from much rounder edge-on spheroids. For this reason the fraction of disks-like systems hidden in the early-type category has been a matter of debate for decades. The solution to the problem comes from observations of the stellar kinematics: the stars in a thin disk rotate much faster than those in a rounder spheroid. This implies that the kinematics makes it possible to recognize a disk from a spheroid at any inclination. However it requires complex and time-consuming observations.

The new results were unexpected and reveal a new paradigm for early-type galaxies. For the first time, it was found that the overwhelming majority of the early-type galaxies in the nearby Universe does not consist of roundish spheroidal objects, but instead has disks and mostly resembles spiral galaxies with the gas and dust removed. Only a tiny fraction of the early-type galaxies - the "slow rotators" - are genuine spheroids. This indicates that Hubble's classic tuning-fork gives a misleading description of galaxy structure.

For more information, please contact:

Prof. Dr. Tom Oosterloo, senior astronomer. Tel.: +31 521 595 779. E-mail: oosterloo@astron.nl.

Femke Boekhorst, PR & Communication. Tel.: +31 521 595 204. E-mail: boekhorst@astron.nl.


Caption to the figure: Maps of the observed velocity of the stars in the volume-limited sample of 260 early-type galaxies of the ATLAS3D survey. Red/blue colours indicate stars moving away/towards us respectively. Fast rotating and disk-like galaxies are characterized by two large and symmetric red/blue peaks at the two sides of the centre. This figure shows that this class of objects constitutes the vast majority of the sample.

More information:

Introduction to the ATLAS3D project: Cappellari et al. (2011, MNRAS, 413, 813: http://dx.doi.org/10.1111/j.1365-2966.2010.18174.x )

The kinematic classification of galaxies: Krajnović et al. (2011, MNRAS, in press: http://adsabs.harvard.edu/abs/2011arXiv1102.3801K), and Emsellem et al. (2011, MNRAS, in press: http://dx.doi.org/10.1111/j.1365-2966.2011.18496.x )

The comb classification diagram: Cappellari et al. (2011, MNRAS, in press: http://adsabs.harvard.edu/abs/2011arXiv1104.3545C )

The project website, including the full list of ATLAS3D papers, published data, and details on observations at other wavelengths: http://purl.org/atlas3d .

ATLAS3D Team Members:

Katey Alatalo (UC Berkeley [USA]) Leo Blitz (UC Berkeley [USA]) Maxime Bois (Observatoire de Lyon [France]) Frederic Bournaud (CEA, Paris-Saclay [France]) Martin Bureau (University of Oxford [UK]) Michele Cappellari (University of Oxford [UK]) Roger L. Davies (University of Oxford [UK]) Timothy A. Davis (University of Oxford [UK]) P. T. de Zeeuw (ESO, Garching [Germany]; Leiden University [The Netherlands]) Pierre-Alain Duc (Laboratoire AIM, Paris-Saclay [France]) Eric Emsellem (ESO, Garching [Germany]; Observatoire de Lyon [France]) Sadegh Khochfar (MPE, Garching [Germany]) Davor Krajnovic (ESO, Garching [Germany]) Harald Kuntschner (ESO, Garching [Germany]) Pierre-Yves Lablanche (Observatoire de Lyon [France]) Richard M. McDermid (Gemini Observatory, Hilo [USA]) Raffaella Morganti (ASTRON, Groningen University [The Netherlands]) Thorsten Naab (MPIA, Garching [Germany]) Tom Oosterloo (ASTRON, Groningen University [The Netherlands]) Marc Sarzi (University of Hertfordshire [UK]) Nicholas Scott (University of Oxford [UK]) Paolo Serra (ASTRON, Dwingeloo [The Netherlands]) A. Weijmans (Dunlap Inst., Univ. of Toronto, [Canada]) Lisa M. Young (New Mexico Tech, Socorro [USA]).

Duo of Big Telescopes Probes the Depths of Binary Star Formation

Figure 1: A composite image toward Taurus FS A binary system. The green color shows the intensity of visible light, based on optical data from the Hubble Space Telescope. The red color displays near-infrared data from the Subaru Telescope. The ellipse marks an artifact from data processing of the central bright star. The dashed lines denote the directions of the support of the secondary mirror of the telescope. The field of view is 16.5" x 17.5". North is up, and east is to the left.

Figure 2: The polarization distribution in visible light, overlaid on the visible image (top) and near-infrared image (bottom). The color-coding refers to the offset from the expected centro-symmetric pattern around FS A star and FS B star. The blue and red colors show the circular pattern around FS A while the green encircles FS B. The area toward the southeast of FS A is bright in the near infrared, and the offset, denoted by the yellow color, is larger. The fields of view are 19" x 31" (top) and 14" x 17" (bottom), respectively. North is up and east is to the left.

A team of researchers from four Japanese universities (Kobe, Saitama, Osaka, and Tokyo) has been able to delineate the intricate structure of the circumbinary disk that surrounds a young binary star system from the observation with the Subaru Telescope and the Hubble Space Telescope. By using different wavelengths to examine the system's internal structure, they succeeded in demonstrating a distinct color difference between its northern and southern portions (figure 1). The researchers are now prepared to apply their approach of combining optical and near-infrared observations to other regions of binary formation.

Previous observations have demonstrated that protoplanetary disks, composed of a ring of dense gas surrounding a star like our Sun, not only accompany many infant stars but also are sites that generate planetary systems such as the one to which our Earth belongs. Therefore, these disks provide important information about the formation of stars and planets.

Past observations have focused on the protoplanetary disks of single stars. However, stellar research reveals that the majority of stars are members of binary or multiple star systems rather than ones composed of a single star. The research team addressed the issue of limited research on binary systems by pointing the Subaru Telescope toward the FS star system in the constellation Taurus. The separation between the primary (A) and companion (B) stars is 20 arc seconds (2800 AU; astronomical unit, the distance between the Sun and the Earth) and the FS A star itself is also a binary system with only 0.2 arc seconds (30 AU) of separation between its stars. The research team succeeded in detecting a circumbinary disk by using the Subaru Telescope's near-infrared camera CIAO (Coronagraphic Imager with Adaptive Optics), which blocks out the bright light of the central star. The disk's size of 630 AU is equivalent to the aphelion (the furthest point from the Sun in its orbit) of Sedona, one of the trans-Neptunian objects.

The team then compared its near-infrared image with the optical image taken by the Advanced Camera System (ACS) aboard the Hubble Space Telescope (HST). The area north of the FS A binary is brighter in the visible light (optical), while that south of the binary stands out in the near-infrared. In other words, the north is blue, and the south is red. The protoplanetary disk reflects the visible or the infrared light from the central star, but it does not emit light by itself. The highly distinct color contrast between the northern and southern portions of FS A's protoplanetary disk is a very unique characteristic of the system.

The question becomes why the color is different in these regions around the binary. Part of the answer relates to the degree of the polarization dispersed from the surface of the disk. Regardless of whether the light is visible or near-infrared, it displays the properties of a wave as well as a particle, and its reflection shows polarization. The degree and the direction of the polarization provide information about the object that reflects the light. This is why measurement of the polarization is important for understanding the structure of the protoplanetary disk. The observation with the Hubble Space Telescope included information on polarization, and figure 2 shows the distribution of the polarized light. The majority of the disk shows a typical concentric pattern around the central star. Other protoplanetary disks show similar patterns.

In addition to its circular pattern, the outer region to the north reflects the light from the FS B star, which is much further away from the FS A system. The research team interpreted this feature as an effect of abundant interstellar material in front of the FS A circumbinary disk and the influence of the FS B. However, the polarization data show that the inner region to the north is part of the protobinary disk surrounding the FS A binary. The mystery of color difference remains.

In sum, the research team established that there is a distinct color difference between the areas to the north and south of the circumbinary disk of the FS A star. They want to continue observations of protoplanetary disks so that they can identify their common characteristics and chronicle their evolution. Their ultimate goal is to understand the planetary formation process in circumstellar/circumbinary disks.

Reference:
"High-Resolution Optical and Near-Infrared Images of the FS Tauri Circumbinary Disk", Tomonori Hioki, Yoichi Itoh, Yumiko Oasa, Misato Fukagawa, Masahiko Hayashi. June 2011 issue of the Publications of the Astronomical Society of Japan.

Monday, June 20, 2011

A Solar Flare That Will Blow Your Socks Off

By now many of you who follow the Sun have probably heard about the “solar flare that will blow your socks off,” which occurred in early morning of Sunday June 7. Here at the Chandra X-ray Center we watched it too -- with some pride as our colleagues downstairs with the Solar Dynamics Observatory were responsible for some of the movies that were being circulated around the Internet. On the one hand, an M2 is a medium-sized event and not usually a big deal. On the other hand, I also thought of a slogan written on my whiteboard a few years ago, “West limb worry.”

Having a Solar Blast

The reason I wrote that on my board was because of the "Parker spiral" and its relationship between the western limb of the Sun and the Earth. The Parker spiral is the name for the path the magnetic field takes through our Solar System. It doesn't simply move straight outward from the Sun, but instead wraps around the Sun due to the stellar rotation. When the magnetic field leaves the Sun, it travels perpendicular to the Sun's surface. But as the Sun rotates, the next field lines are dragged backwards. The resulting shape is a spiral and it is wound such that the Western limb of the sun as viewed from the Earth is connected to the Earth. So I worried… This is as much we can do about it immediately: if we see radiation rates increasing we can manually move the science instruments to a safe position, but it's difficult to estimate how quickly the ions from an event like that will reach the Earth.

At 1:45 pm Eastern on Tuesday, most the Chandra Science Center staff was in a group meeting discussing future possible endeavors for the division. Then my supervisor's pager went off, which I thought it was pretty amusing. Then someone else's phone went off, and I wondered why everybody hadn't shifted their phones to vibrate for the meeting. Then a little part of my brain woke up and told me to check my phone. It started vibrating in my hand as the alert went off to tell me that the spacecraft had autonomously moved the science instruments into the safe configuration.

Conveniently, most of the science team was already assembled due to the staff meeting and we simply found ourselves a quiet room next the meeting room and dialed in on a teleconference with the remainder of the Flight Operations Team. This resulted in a rather amusing scene of eight of us discussing who had the best speaker on their cell phone, followed by the discovery of the feedback caused by operating more than one speaker phone at the same table.

This was our first radiation shutdown in almost five years. It took us a few minutes for us to remember what the procedures were, and then each of us started going through our own checklists. This included the chief engineer checking that the spacecraft was in a stable position and good power was coming in. The mission planners looked up what observations were currently not being made and how and how important it was for them to be made and as soon as possible or in a timely manner. The instrument teams checked the specific health of their instruments and that the instruments were where they were supposed to be. I was checking the current radiation environment for Chandra as well as a series of other spacecraft such as ACE and GOES. After a brief discussion confirming that the spacecraft was safe and that the events appeared to be related to the solar flare, we were left with how to proceed from here.

This can be tricky because what we were witnessing was the arrival of the fastest high-energy protons that left the Sun. Still to come were “softer” (low-energy) protons that could take up to two more days to arrive. So we were left with a couple of choices; 1) simply sit things out for about two and a half days and restart science with high confidence after the entire storm had passed; or 2) try to pick up the schedule as quickly as possible with an observation which would be minimally affected by moderate radiation levels.

The second path would only be possible if radiation levels dropped within 16 hours. If they didn't drop, we would have wasted a lot of manpower creating a schedule we would never use and still have to write a new schedule the pickup 48 hours from then. On the other hand, picking up the schedule in 16 hours would add back nearly a day's worth of science on an instrument that costs tens of thousands of dollars a day to operate and is oversubscribed by seven to one. We chose plan two.

About eight hours after the shutdown, we had one of our thrice daily contacts with the spacecraft. At this time we checked the direct radiation environment and found it was to hot for us to restart activities. We would have exactly one more chance to check the radiation environment and decide whether or not we could restart loads or we would have to sit out 48 hours.

That chance came around seven o'clock Wednesday morning at which point the radiation levels had settled down enough for us to restart loads. We started with a matched set of observations of Alpha Centauri and things have been fine ever since.

For us, not only was this storm beautiful to behold, a credit to the Solar Dynamics Observatory, but also a reminder of how fickle space weather can be, even during this period of one of the quietest solar maximums on record.

Scott Wolk

GeMS First Light: A New Generation of Adaptive Optics Begins

Figure 1. The engineering first light image obtained with GeMS and the Gemini South Adaptive Optics Imager GSAOI on April 19, 2011. The field of view is 85 x 85 arcseconds and the wavelength is 2.12 microns. Strehl ratio and full-width at half-maximum values for all stars are shown in the insets. This image was obtained after only 30 minutes of focusing and optimization – it is by no means representative of what is expected from the fully-commissioned system. However, it is very encouraging and already illustrates the main advantage of MCAO, which is a relatively uniform compensation across a large field of view. Note that the poorer image quality on the left edge is expected, as these stars are outside the constellation defined by the three bright stars in the right half used to control Tip-Tilt.Download full-resolution PNG 0.9 MB

In early April 2011, after more than a decade of effort, the Gemini Multi-Conjugate Adaptive Optics System (GeMS) saw starlight for the first time. With this milestone GeMS kicked off a new era in adaptive optics (AO) technologies both for Gemini and for future generations of even larger telescopes that will require advanced AO to make them scientifically viable. These first GeMS photons, captured on April 19, 2011 (see Figure 1), kept hopes high for equally successful progress when commissioning resumes in late 2011 and then for system verification in early 2012.

Adaptive Optics is a well-known technology that compensates for image distortions induced by atmospheric turbulence. The vast majority of large telescopes in the world are now equipped with AO systems of various kinds, and many use lasers to create artificial stars (laser guide stars, LGS) in order to probe and correct for atmospheric turbulence over a larger portion of the sky (e.g. Altair at Gemini North). Multi-Conjugate Adaptive Optics (MCAO) is a relatively novel concept, in which the distortions are compensated by using not one, but a series of deformable mirrors and multiple guide stars. In effect, this provides compensation in three dimensions versus the two dimensions for classical (existing) AO systems. The impact on data is that there is a ten-fold increase in the size of the corrected field of view and significantly more uniform corrections across the entire field than classical AO. GeMS is the first instrument to use MCAO with multiple laser guide stars – thus explaining the long development cycle which began in 2001.

In March 2010 Gemini received the 50-watt sodium laser built by Lockheed Martin Coherent Technology. Following this, Canopus, the GeMS optical bench, made its much-anticipated trek from the Gemini South Base Facility integration laboratory to the Cerro Pachón summit in November 2010. The installation on the telescope in January 2011 marked the beginning of a five-month commissioning marathon for the Gemini MCAO team. The first two commissioning periods – one week in January and one in February – were dedicated to the laser and associated subsystems, beam transfer optics, laser launch telescope and various laser safety systems. The laser generally performed well, delivering between 45 and 60 watts of yellow (sodium) light (see the June 2011 issue of GeminiFocus, pages 23-28). After initial concerns about the laser guide star spot size we regularly obtained spot sizes of 1.3 arcseconds as viewed by the telescope’s acquisition camera system.

The commissioning of Canopus started in March, with two subsequent runs in April and May, for a total of nine clear nights. To date, the commissioning has concentrated on functionality since this very complex instrument includes multiple subsystems linked together by closed loops and offloads that the MCAO team had to characterize, debug and optimize. Currently, almost all subsystems, loops and offloads are working, which include: the main LGS loop, the natural guide star (NGS) loops, all telescope offloads, the LGS and NGS acquisition sequences, and many others. The technical first light image shown in Figure 1 was obtained on April 19 with plans to continue commissioning through May. However, bad weather and various technical issues prevented making much more progress in areas such as performance optimization and characterization as well as plans to acquire additional astronomical images which would demonstrate the system’s capabilities more dramatically.

In early June 2011, GeMS entered a five-month rework period. Significant work on the laser to insure better beam quality, stability and reliability is planned. Stability issues in the Beam Transfer Optics will also be addressed. Finally, various Canopus subsystems will be upgraded, with a particular effort to improve the optical throughput of the natural guide star wavefront sensors. Commissioning should resume at the end of 2011, with a focus on performance and integration with the observatory high-level software. System Verification (SV) is expected to occur in the first half of 2012.