Tuesday, January 31, 2012

IBEX: Glimpses of the Interstellar Material Beyond our Solar System

IBEX has directly sampled multiple heavy elements from the Local Interstellar Cloud for the first time. Credit: NASA/Goddard Scientific Visualization Studio. Download video

A great magnetic bubble surrounds the solar system as it cruises through the galaxy. The sun pumps the inside of the bubble full of solar particles that stream out to the edge until they collide with the material that fills the rest of the galaxy, at a complex boundary called the heliosheath. On the other side of the boundary, electrically charged particles from the galactic wind blow by, but rebound off the heliosheath, never to enter the solar system. Neutral particles, on the other hand, are a different story. They saunter across the boundary as if it weren't there, continuing on another 7.5 billion miles for 30 years until they get caught by the sun's gravity, and sling shot around the star.

There, NASA's Interstellar Boundary Explorer lies in wait for them. Known as IBEX for short, this spacecraft methodically measures these samples of the mysterious neighborhood beyond our home. IBEX scans the entire sky once a year, and every February, its instruments point in the correct direction to intercept incoming neutral atoms. IBEX counted those atoms in 2009 and 2010 and has now captured the best and most complete glimpse of the material that lies so far outside our own system.

The results? It's an alien environment out there: the material in that galactic wind doesn't look like the same stuff our solar system is made of.

Neutral atoms from the galactic wind sweep past the solar system's magnetic boundary, the heliosheath, and travel some 30 years into our solar system toward the sun. NASA's Interstellar Boundary Explorer (IBEX) can observe those atoms and provide information about the mysterious neighborhood outside our home. Credit: NASA/Goddard Conceptual Image Lab. Download video

"We've directly measured four separate types of atoms from interstellar space and the composition just doesn't match up with what we see in the solar system," says Eric Christian, mission scientist for IBEX at NASA's Goddard Space Flight Center in Greenbelt, Md. "IBEX's observations shed a whole new light on the mysterious zone where the solar system ends and interstellar space begins."

More than just helping to determine the distribution of elements in the galactic wind, these new measurements give clues about how and where our solar system formed, the forces that physically shape our solar system, and even the history of other stars in the Milky Way.

NASA's Interstellar Boundary Explorer (IBEX) has found that there's more oxygen in our solar system than there is in the nearby interstellar material. That suggests that either the sun formed in a different part of the galaxy or that outside our solar system life-giving oxygen lies trapped in dust or ice grains unable to move freely in space. Credit: NASA/Goddard. View larger

In a series of science papers appearing in the Astrophysics Journal on January 31, 2012, scientists report that for every 20 neon atoms in the galactic wind, there are 74 oxygen atoms. In our own solar system, however, for every 20 neon atoms there are 111 oxygen atoms. That translates to more oxygen in any given slice of the solar system than in the local interstellar space.

"Our solar system is different than the space right outside it and that suggests two possibilities," says David McComas the principal investigator for IBEX at the Southwest Research Institute in San Antonio, Texas. "Either the solar system evolved in a separate, more oxygen-rich part of the galaxy than where we currently reside or a great deal of critical, life-giving oxygen lies trapped in interstellar dust grains or ices, unable to move freely throughout space." Either way, this affects scientific models of how our solar system – and life – formed.

Studying the galactic wind also provides scientists with information about how our solar system interacts with the rest of space, which is congruent with an important IBEX goal. Classified as a NASA Explorer Mission -- a class of smaller, less expensive spacecraft with highly focused research objectives -- IBEX's main job is to study the heliosheath, that outer boundary of the solar system's magnetic bubble -- or heliosphere -- where particles from the solar wind meet the galactic wind.

Previous spacecraft have already provided some information about the way the galactic wind interacts with the heliosheath. Ulysses, for one, observed incoming helium as it traveled past Jupiter and measured it traveling at 59,000 miles per hour. IBEX's new information, however, shows the galactic wind traveling not only at a slower speed -- around 52,000 miles per hour -- but from a different direction, most likely offset by some four degrees from previous measurements. Such a difference may not initially seem significant, but it amounts to a full 20% difference in how much pressure the galactic wind exerts on the heliosphere.

The galactic wind streams toward the sun from the direction of Scorpio and IBEX has found that it travels at 52,000 miles an hour. The speed of the galactic wind and its subsequent pressure on the outside of the solar system's boundary affects the shape of the heliosphere as it travels through space. Credit: NASA/Goddard Scientific Visualization Studio. View larger

"Measuring the pressure on our heliosphere from the material in the galaxy and from the magnetic fields out there," says Christian, "will help determine the size and shape of our solar system as it travels through the galaxy."

These IBEX measurements also provide information about the cloud of material in which the solar system currently resides. This cloud is called the local interstellar cloud, to differentiate it from the myriad of particle clouds throughout the Milky Way, each traveling at different speeds. The solar system and its heliosphere moved into our local cloud at some point during the last 45,000 years.

Since the older Ulysses observations of the galactic wind speed was in between the speeds expected for the local cloud and the adjacent cloud, researchers thought perhaps the solar system didn't lie smack in the middle of this cloud, but might be at the boundary, transitioning into a new region of space. IBEX's results, however, show that we remain fully in the local cloud, at least for the moment.

"Sometime in the next hundred to few thousand years, the blink of an eye on the timescales of the galaxy, our heliosphere should leave the local interstellar cloud and encounter a much different galactic environment," McComas says.

In addition to providing insight into the interaction between the solar system and its environment, these new results also hold clues about the history of material in the universe. While the big bang initially created hydrogen and helium, only the supernovae explosions at the end of a giant star's life can spread the heavier elements of oxygen and neon through the galaxy. Knowing the amounts of such elements in space can help map how the galaxy has evolved and changed over time.

NASA's Interstellar Boundary Explorer (IBEX) studies the outer boundaries of the solar system where particles from the solar wind collide with particles from the galactic wind. Credit: NASA. View larger

"This set of papers provide many of the first direct measurements of the interstellar medium around us," says McComas. "We've been trying to understand our galaxy for a long time, and with all of these observations together, we are taking a major step forward in knowing what the local part of the galaxy is like."

Voyager 1 could cross out of our solar system within the next few years. By combining the data from several sets of NASA instruments – Ulysses, Voyager, IBEX and others – we are on the precipice of stepping outside and understanding the complex environment beyond our own frontier for the first time.

The Southwest Research Institute developed and leads the IBEX mission with a team of national and international partners. The spacecraft is one of NASA's series of low-cost, rapidly developed missions in the Small Explorers Program. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the program for the agency's Science Mission Directorate.

For more information about the IBEX mission, go to:

http://www.nasa.gov/ibex - Additional downloadable media

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, MD

Young Stars at Home in an Ancient Cluster

NGC 6752
Credit: ESA/Hubble & NASA

Looking like a hoard of gems fit for an emperor’s collection, this deep sky object called NGC 6752 is in fact far more worthy of admiration. It is a globular cluster, and at over 10 billion years old is one the most ancient collections of stars known. It has been blazing for well over twice as long long as our Solar System has existed.

NGC 6752 contains a high number of “blue straggler” stars, some of which are visible in this image. These stars display characteristics of stars younger than their neighbours, despite models suggesting that most of the stars within globular clusters should have formed at approximately the same time. Their origin is therefore something of a mystery.

Studies of NGC 6752 may shed light on this situation. It appears that a very high number — up to 38% — of the stars within its core region are binary systems. Collisions between stars in this turbulent area could produce the blue stragglers that are so prevalent.

Lying 13 000 light-years distant, NGC 6752 is far beyond our reach, yet the clarity of Hubble’s images brings it tantalisingly close.


Thursday, January 26, 2012

NASA's Kepler Announces 11 Planetary Systems Hosting 26 Planets

Kepler's Planetary Systems: The artist's rendering depicts the multiple planet systems discovered by NASA's Kepler mission. Image credit: NASA Ames/Jason Steffen, Fermilab Center for Particle Astrophysics.

Kepler's Planetary Systems' Orbits: The image shows an overhead view of orbital positions of the planets in systems with multiple transiting planets discovered by NASA's Kepler mission. Image credit: NASA Ames/Dan Fabrycky, University of California, Santa Cruz

NASA's Kepler mission has discovered 11 new planetary systems hosting 26 confirmed planets. These discoveries nearly double the number of verified Kepler planets and triple the number of stars known to have more than one planet that transits, or passes in front of, its host star. Such systems will help astronomers better understand how planets form.

The planets orbit close to their host stars and range in size from 1.5 times the radius of Earth to larger than Jupiter. Fifteen of them are between Earth and Neptune in size, and further observations will be required to determine which are rocky like Earth and which have thick gaseous atmospheres like Neptune. The planets orbit their host star once every six to 143 days. All are closer to their host star than Venus is to our sun.

"Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky," said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Now, in just two years staring at a patch of sky not much bigger than your fist, Kepler has discovered more than 60 planets and more than 2,300 planet candidates. This tells us that our galaxy is positively loaded with planets of all sizes and orbits."

Kepler identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars to detect when a planet passes in front of the star. That passage casts a small shadow toward Earth and the Kepler spacecraft.

“Confirming that the small decrease in the star's brightness is due to a planet requires additional observations and time-consuming analysis," said Eric Ford, associate professor of astronomy at the University of Florida and lead author of the paper confirming Kepler-23 and Kepler-24. “We verified these planets using new techniques that dramatically accelerated their discovery.”

Each of the new confirmed planetary systems contains two to five closely spaced transiting planets. In tightly packed planetary systems, the gravitational pull of the planets among themselves causes one planet to accelerate and another planet to decelerate along its orbit. The acceleration causes the orbital period of each planet to change. Kepler detects this effect by measuring the changes, or so-called Transit Timing Variations (TTVs).

Planetary systems with TTVs can be verified without requiring extensive ground-based observations, accelerating confirmation of planet candidates. The TTV detection technique also increases Kepler's ability to confirm planetary systems around fainter and more distant stars.

“By precisely timing when each planet transits its star, Kepler detected the gravitational tug of the planets on each other, clinching the case for ten of the newly announced planetary systems,” said Dan Fabrycky, Hubble Fellow at the University of California, Santa Cruz and lead author for a paper confirming Kepler-29, 30, 31 and 32."

Five of the systems (Kepler-25, Kepler-27, Kepler-30, Kepler-31 and Kepler-33) contain a pair of planets where the inner planet orbits the star twice during each orbit of the outer planet. Four of the systems (Kepler-23, Kepler-24, Kepler-28 and Kepler-32) contain a pairing where the outer planet circles the star twice for every three times the inner planet orbits its star.

“These configurations help to amplify the gravitational interactions between the planets, similar to how my sons kick their legs on a swing at the right time to go higher,” said Jason Steffen, the Brinson postdoctoral fellow at Fermilab Center for Particle Astrophysics in Batavia, Ill., and lead author of a paper confirming Kepler-25, 26, 27 and 28.

The system with the most planets among these discoveries is Kepler-33, a star that is older and more massive than our sun. Kepler-33 hosts five planets, ranging in size from 1.5 to 5 times that of Earth and all located closer to their star than any planet is to the sun.

The properties of a star provide clues for planet detection. The decrease in the star's brightness and duration of a planet transit combined with the properties of its host star present a recognizable signature. When astronomers detect planet candidates that exhibit similar signatures around the same star the likelihood of any of these planet candidates being a false positive is very low.

“The approach that was used to verify the Kepler-33 planets shows that the overall reliability of Kepler's candidate multiple transiting systems is quite high," said Jack Lissauer, planetary scientist at NASA Ames Research Center at Moffett Field, Calif., and lead author of the paper confirming Kepler-33. “This is a validation by multiplicity.”

  • These discoveries are published in the Astrophysical Journal and the Monthly Notices of the Royal Astronomical Society and can be viewed at:
  • J Lissauer et al - Almost All of Kepler's Multiple Planet Candidates are Planets, and Kepler-33 5-planet system
  • E Ford et al - Transit Timing Observations from Kepler: II. Confirmation of Two Multiplanet Systems via a Non-parametric Correlation Analysis. Confirms KOI-168=Kepler-23 and KOI 1102=Kepler-24
  • J Steffen et al - Transit Timing Observations from Kepler: III. Confirmation of 4 Multiple Planet Systems by a Fourier-Domain Study of Anti-correlated Transit Timing Variations
  • D Fabrycky et al - Transit Timing Observations From Kepler: IV. Confirmation Of 4 Multiple Planet Systems By Simple Physical Models
Ames Research Center in Moffett Field, Calif., manages Kepler's ground system development, mission operations and science data analysis. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., managed the Kepler mission's development.

Ball Aerospace and Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

The Space Telescope Science Institute in Baltimore archives, hosts and distributes Kepler science data. Kepler is NASA's 10th Discovery Mission and is funded by NASA's Science Mission Directorate at the agency's headquarters in Washington.

For more information about the Kepler mission, visit: http://www.nasa.gov/kepler

Kepler's Planetary Systems in Motion: The animation shows an overhead view of the orbital position of the planets in systems with multiple transiting planets discovered by NASA's Kepler mission. All the colored planets have been verified. More vivid colors indicate planets that have been confirmed by their gravitational interactions with each other or the star. Several of these systems contain additional planet candidates (shown in grey) that have not yet been verified. Image credit: NASA Ames/Dan Fabrycky, University of California, Santa Cruz

Transit Timing Variations: The animation shows the difference between planet transit timing of single and multiple planet system. In tightly packed planetary systems, the gravitational pull of the planets among themselves causes one planet to accelerate and another planet to decelerate along its orbit. The acceleration causes the orbital period of each planet to change. Kepler detects this effect by measuring the change known as Transit Timing Variations (TTVs). Image credit: NASA Ames/Kepler mission

Michele Johnson
NASA Ames Research Center

Wednesday, January 25, 2012

The Wild Early Lives of Today's Most Massive Galaxies

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Distant star-forming galaxies in the early Universe

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The position of the Extended Chandra Deep Field South in the constellation of Fornax

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Distant star-forming galaxies in the early Universe (zoom)

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Distant star-forming galaxies in the early Universe (pan)

Using the APEX telescope, a team of astronomers has found the strongest link so far between the most powerful bursts of star formation in the early Universe, and the most massive galaxies found today. The galaxies, flowering with dramatic starbursts in the early Universe, saw the birth of new stars abruptly cut short, leaving them as massive — but passive — galaxies of aging stars in the present day. The astronomers also have a likely culprit for the sudden end to the starbursts: the emergence of supermassive black holes.

Astronomers have combined observations from the LABOCA camera on the ESO-operated 12-metre Atacama Pathfinder Experiment (APEX) telescope [1] with measurements made with ESO’s Very Large Telescope, NASA’s Spitzer Space Telescope, and others, to look at the way that bright, distant galaxies are gathered together in groups or clusters.

The more closely the galaxies are clustered, the more massive are their halos of dark matter — the invisible material that makes up the vast majority of a galaxy’s mass. The new results are the most accurate clustering measurements ever made for this type of galaxy.

The galaxies are so distant that their light has taken around ten billion years to reach us, so we see them as they were about ten billion years ago [2]. In these snapshots from the early Universe, the galaxies are undergoing the most intense type of star formation activity known, called a starburst.

By measuring the masses of the dark matter halos around the galaxies, and using computer simulations to study how these halos grow over time, the astronomers found that these distant starburst galaxies from the early cosmos eventually become giant elliptical galaxies — the most massive galaxies in today’s Universe.

“This is the first time that we've been able to show this clear link between the most energetic starbursting galaxies in the early Universe, and the most massive galaxies in the present day," explains Ryan Hickox (Dartmouth College, USA and Durham University, UK), the lead scientist of the team.

Furthermore, the new observations indicate that the bright starbursts in these distant galaxies last for a mere 100 million years — a very short time in cosmological terms — yet in this brief time they are able to double the quantity of stars in the galaxies. The sudden end to this rapid growth is another episode in the history of galaxies that astronomers do not yet fully understand.

“We know that massive elliptical galaxies stopped producing stars rather suddenly a long time ago, and are now passive. And scientists are wondering what could possibly be powerful enough to shut down an entire galaxy’s starburst,” says Julie Wardlow (University of California at Irvine, USA and Durham University, UK), a member of the team.

The team’s results provide a possible explanation: at that stage in the history of the cosmos, the starburst galaxies are clustered in a very similar way to quasars, indicating that they are found in the same dark matter halos. Quasars are among the most energetic objects in the Universe — galactic beacons that emit intense radiation, powered by a supermassive black hole at their centre.

There is mounting evidence to suggest the intense starburst also powers the quasar by feeding enormous quantities of material into the black hole. The quasar in turn emits powerful bursts of energy that are believed to blow away the galaxy’s remaining gas — the raw material for new stars — and this effectively shuts down the star formation phase.

“In short, the galaxies’ glory days of intense star formation also doom them by feeding the giant black hole at their centre, which then rapidly blows away or destroys the star-forming clouds,” explains David Alexander (Durham University, UK), a member of the team.


[1] The 12-metre-diameter APEX telescope is located on the Chajnantor plateau in the foothills of the Chilean Andes. APEX is a pathfinder for ALMA, the Atacama Large Millimeter/submillimeter Array, a revolutionary new telescope that ESO, together with its international partners, is building and operating, also on the Chajnantor plateau. APEX is itself based on a single prototype antenna constructed for the ALMA project. The two telescopes are complementary: for example, APEX can find many targets across wide areas of sky, which ALMA will be able to study in great detail. APEX is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO.

[2] These distant galaxies are known as submillimetre galaxies. They are very bright galaxies in the distant Universe in which intense star formation occurs. Because of this extreme distance, their infrared light from dust grains heated by starlight is redshifted into longer wavelengths, and the dusty galaxies are therefore best observed in submillimetre wavelengths of light.
More information

This research is presented in a paper to appear in the journal Monthly Notices of the Royal Astronomical Society on 26 January 2012.

The team is composed of Ryan C. Hickox (Dartmouth College, Hanover, USA; Department of Physics, Durham University (DU); STFC Postdoctoral Fellow, UK), J. L. Wardlow (Department of Physics & Astronomy, University of California at Irvine, USA; Department of Physics, DU, UK), Ian Smail (Institute for Computational Cosmology, DU, UK), A. D. Myers (Department of Physics and Astronomy, University of Wyoming, USA), D. M. Alexander (Department of Physics, DU, UK), A. M. Swinbank (Institute for Computational Cosmology, DU, UK), A. L. R. Danielson (Institute for Computational Cosmology, DU, UK), J. P. Stott (Department of Physics, DU, UK), S. C. Chapman (Institute of Astronomy, Cambridge, UK), K. E. K. Coppin (Department of Physics, McGill University, Canada), J. S. Dunlop (Institute for Astronomy, University of Edinburgh, UK), E. Gawiser (Department of Physics and Astronomy, The State University of New Jersey, USA), D. Lutz (Max-Planck-Institut für extraterrestrische Physik, Germany), P. van der Werf (Leiden Observatory, Leiden University, The Netherlands), A. Weiß (Max-Planck-Institut für Radioastronomie, Germany).

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

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

Research paper
Information about APEX
Images related to APEX


Ryan Hickox
Dartmouth College
Hanover, New Hampshire, USA
Tel: +1 603 646 2962
Email: ryan.c.hickox@dartmouth.edu

Douglas Pierce-Price
ESO ALMA/APEX Public Information Officer
Garching, Germany
Tel: +49 89 3200 6759
Email: dpiercep@eso.org

Tuesday, January 24, 2012

Barred Spiral Galaxy Swirls in the Night Sky

NGC 2217
Credit: ESO

This image shows the swirling shape of galaxy NGC 2217, in the constellation of Canis Major (The Great Dog). In the central region of the galaxy is a distinctive bar of stars within an oval ring. Further out, a set of tightly wound spiral arms almost form a circular ring around the galaxy. NGC 2217 is therefore classified as a barred spiral galaxy, and its circular appearance indicates that we see it nearly face-on.

The outer spiral arms have a bluish colour, indicating the presence of hot, luminous, young stars, born out of clouds of interstellar gas. The central bulge and bar are yellower in appearance, due to the presence of older stars. Dark streaks can also be seen in places against the galaxy’s arms and central bulge, where lanes of cosmic dust block out some of the starlight.

The majority of spiral galaxies in the local Universe — including our own Milky Way — are thought to have a bar of some kind, and these structures play an important role in the development of a galaxy. They can, for example, funnel gas towards the centre of the galaxy, helping to feed a central black hole, or to form new stars.

Monday, January 23, 2012

Seeing Quadruple

UZC J224030.2+032131
Credit: ESA/Hubble & NASA

This NASA/ESA Hubble Space Telescope picture may trick you into thinking that the galaxy in it — known as UZC J224030.2+032131 — has not one but five different nuclei. In fact, the core of the galaxy is only the faint and diffuse object seen at the centre of the cross-like structure formed by the other four dots, which are images of a distant quasar located in the background of the galaxy.

The picture shows a famous cosmic mirage known as the Einstein Cross, and is a direct visual confirmation of the theory of general relativity. It is one of the best examples of the phenomenon of gravitational lensing — the bending of light by gravity as predicted by Einstein in the early 20th century. In this case, the galaxy’s powerful gravity acts as a lens that bends and amplifies the light from the quasar behind it, producing four images of the distant object.

The quasar is seen as it was around 11 billion light-years ago, in the direction of the constellation of Pegasus, while the galaxy that works as a lens is some ten times closer. The alignment between the two objects is remarkable (within 0.05 arcseconds), which is in part why such a special type of gravitational lensing is observed.

This image is likely the sharpest image of the Einstein Cross ever made, and was produced by Hubble’s Wide Field and Planetary Camera 2, and has a field of view of 26 by 26 arcseconds.

Saturday, January 21, 2012

Comet Corpses in the Solar Wind

A paper published in today's issue of Science raises an intriguing new possibility for astronomers: unearthing comet corpses in the solar wind. The new research is based on dramatic images of a comet disintegrating in the sun's atmosphere last July.

Comet Lovejoy grabbed headlines in Dec. 2011 when it plunged into the sun's atmosphere and emerged again relatively intact. But it was not the first comet to graze the sun. Last summer a smaller comet took the same trip with sharply different results. Comet C/2011 N3 (SOHO) was completely destroyed on July 6, 2011, when it swooped 100,000 km above the stellar surface. NASA's Solar Dynamics Observatory (SDO) recorded the disintegration.

Comet C/2011 N3 fragments as it passes through the sun's atmosphere on July 6, 2011. Credit: Solar Dynamics Observatory/K. Schrijver et al [larger image]


An extreme ultraviolet movie recorded by SDO shows comet Comet C/2011 N3 flying through the sun's atmosphere. [
Quicktime video]

"For the first time, we saw a comet move across the face of the sun and disappear," says Dean Pesnell, a co-author of the Science paper and Project Scientist for SDO at the Goddard Space Flight Center. "It was unprecedented."

In Jan. 20th issue of Science, the research team reported their analysis of the SDO images.

A key finding was the amount of material deposited into the sun's atmosphere. "The comet dissolved into more than a million tons of electrically charged gas," says Pesnell. "We believe these vapors eventually mixed with the solar wind and blew back into the solar system."

Pesnell says it might be possible to detect such "comet corpses" as they waft past Earth. Comets are rich in ice (frozen H2O), so when they dissolve in the hot solar atmosphere, the gaseous remains contain plenty of oxygen and hydrogen. A solar wind stream containing extra oxygen could be a telltale sign of a disintegrated comet. Other elements abundant in comets would provide similar markers.

Comet corpses are probably plentiful. There's a busy family of comets known as "Kreutz sungrazers," thought to be fragments of a giant comet that broke apart hundreds of years ago. Every day or so, SOHO sees one plunge into the sun and vanish. Each disintegration event creates a puff of comet vapor that might be detectable by spacecraft sampling the solar wind.

Why bother? Researchers are beginning to think of sungrazers as 'test particles' for studying the sun's atmosphere--kind of like tossing rocks into a pond. A lot can be learned about the pond by studying the ripples.

Indeed, SDO observed some extraordinary interactions between the sun and the doomed comet. As C/2011 N3 (SOHO) moved through the hot corona, cold gas lifted off the comet's nucleus and rapidly (within minutes) warmed to more than 500,000K, hot enough to shine brightly in SDO's extreme ultraviolet telescopes.

"The evaporating comet gas was glowing as brightly as the sun behind it," marvels Pesnell.

The gas was also rapidly ionized by a process called "charge exchange," which made the gas responsive to the sun's magnetic field. Caught in the grip of magnetic loops which thread the solar corona, the comet's ionized tail wagged back and forth wildly in the moments before final disintegration.

Watching this kind of sun-comet interaction could reveal new things about the thermal and magnetic structure of the solar atmosphere. Likewise, measuring how long it takes for "comet corpses" to reach Earth, and then sampling the gases when they arrive, could be very informative.

Watching this kind of sun-comet interaction could reveal new things about the thermal and magnetic structure of the solar atmosphere. Likewise, measuring how long it takes for "comet corpses" to reach Earth, and then sampling the gases when they arrive, could be very informative.

"Before SDO, no one dreamed we could observe a comet disintegrate inside the sun's atmosphere," says Pesnell who confesses that even he was a skeptic. But now, "I'm a believer."

The original research described in this story may be found in the Jan. 20th edition of Science: Destruction of Sun-grazing comet C/2011 N3 (SOHO) by C. J. Schrijver, J. C. Brown, K. Battams, P. Saint-Hilaire, W. Liu, H. Hudson, and W. D. Pesnell.

Author: Dr. Tony Phillips
Production editor: Dr. Tony Phillips
Credit: Science@NASA

More Information

Comet Lovejoy Plunges into the Sun and Survives
-- Science@NASA

Comet's Demise Observed for the First Time
-- videos from SDO

Some Comets Like it Hot
-- Science@NASA feature story

Sungrazing Comet -- ScienceCast video

Friday, January 20, 2012

Core of Messier 100 in Super High Res

Messier 100, NGC 4321
Credit: ESA/Hubble & NASA

Messier 100 is a perfect example of a grand design spiral galaxy, a type of galaxy with prominent and very well-defined spiral arms. These dusty structures swirl around the galaxy’s nucleus, and are marked by a flurry of star formation activity that dots Messier 100 with bright blue, high-mass stars.

This image from the NASA/ESA Hubble Space Telescope, the most detailed made to date, shows the bright core of the galaxy and the innermost parts of its spiral arms. Messier 100 has an active galactic nucleus — a bright region at the galaxy’s core caused by a supermassive black hole that is actively swallowing material, which radiates brightly as it falls inwards.

The galaxy’s spiral arms also host smaller black holes, including the youngest ever observed in our cosmic neighbourhood, the result of a supernova observed in 1979.

Messier 100 is located in the direction of the constellation of Coma Berenices, about 50 million light-years distant.

The galaxy became famous in the early 1990s with the release of two images of the object taken with Hubble before and after a major repair to the telescope, which illustrated the dramatic improvement in Hubble’s observations.

This image, taken with the high resolution channel of Hubble’s Advanced Camera for Surveys demonstrates the continued evolution of Hubble’s capabilities over two decades in orbit. This image, like all high resolution channel images, has a relatively small field of view: only around 25 by 25 arcseconds.


Source: ESA/Hubble - Space Telescope

Thursday, January 19, 2012

The Helix in New Colours

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VISTA’s look at the Helix Nebula

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The Helix Nebula in the constellation of Aquarius

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Digitized Sky Survey Image of the Helix Nebula

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Infrared/visible light comparison view of the Helix Nebula

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Zooming into the Helix Nebula

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An infrared/visible light comparison of views of the Helix Nebula

ESO’s VISTA telescope, at the Paranal Observatory in Chile, has captured a striking new image of the Helix Nebula. This picture, taken in infrared light, reveals strands of cold nebular gas that are invisible in images taken in visible light, as well as bringing to light a rich background of stars and galaxies.

The Helix Nebula is one of the closest and most remarkable examples of a planetary nebula [1]. It lies in the constellation of Aquarius (The Water Bearer), about 700 light-years away from Earth. This strange object formed when a star like the Sun was in the final stages of its life. Unable to hold onto its outer layers, the star slowly shed shells of gas that became the nebula. It is evolving to become a white dwarf star and appears as the tiny blue dot seen at the centre of the image.

The nebula itself is a complex object composed of dust, ionised material as well as molecular gas, arrayed in a beautiful and intricate flower-like pattern and glowing in the fierce glare of ultraviolet light from the central hot star.

The main ring of the Helix is about two light-years across, roughly half the distance between the Sun and the nearest star. However, material from the nebula spreads out from the star to at least four light-years. This is particularly clear in this infrared view since red molecular gas can be seen across much of the image.

While hard to see visually, the glow from the thinly spread gas is easily captured by VISTA’s special detectors, which are very sensitive to infrared light. The 4.1-metre telescope is also able to detect an impressive array of background stars and galaxies.

The powerful vision of ESO’s VISTA telescope also reveals fine structure in the nebula’s rings. The infrared light picks out how the cooler, molecular gas is organised. The material clumps into filaments that radiate out from the centre and the whole view resembles a celestial firework display.

Even though they look tiny, these strands of molecular hydrogen, known as cometary knots, are about the size of our Solar System. The molecules in them are able to survive the high-energy radiation that emanates from the dying star precisely because they clump into these knots, which in turn are shielded by dust and molecular gas. It is currently unclear how the cometary knots may have originated.


Please note that this text was modified on 18 January 2012 to correct some minor errors.

[1] Planetary nebulae have nothing to do with planets. This confusing name arose because many of them show small bright discs when observed visually and resemble the outer planets in the Solar System, such as Uranus and Neptune. The Helix Nebula, which also bears the catalogue number NGC 7293, is unusual as it appears very large, but also very faint, when viewed through a small telescope.
More information

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

Photos of VISTA


Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

Wednesday, January 18, 2012

Most Distant Dwarf Galaxy Detected

The gravitational lens B1938+666 as seen in the infrared when observed with the 10-meter Keck II telescope with Adaptive Optics on Mauna Kea, Hawaii. In the center is a massive red galaxy 9.8 billion light-years from Earth that acts like a cosmic magnifying glass, distorting the light from an even more distant galaxy, 17.3 billion light-years away. The result is a spectacular Einstein ring image of the background galaxy. The team used distortions within the ring to find evidence for a low-mass dark galaxy, which is a satellite of the foreground lensing galaxy. Using this gravitational lensing effect the mass of the dark galaxy was found to be 200 million times the mass of the Sun, which is similar to the masses of the satellite galaxies found around our own Milky Way, but is 9.8 billion light-years further away.Credit: D. Lagattuta / W. M. Keck Observatory

Kamuela, HI—Scientists have long struggled to detect the dim dwarf galaxies that orbit our own galaxy. So it came as a surprise on Jan. 18 when a team of astronomers using Keck II telescope’s adaptive optics has announced the discovery of a dwarf galaxy halfway across the universe.

The new dwarf galaxy found by MIT’s Dr. Simona Vegetti and colleagues is a satellite of an elliptical galaxy almost 10 billion light-years away from Earth. The team detected it by studying how the massive elliptical galaxy, called JVAS B1938 + 666, serves as a gravitational lens for light from an even more distant galaxy directly behind it. Their discovery was published in the Jan. 18 online edition of the journal Nature.

Like all supermassive elliptical galaxies, JVAS B1938 + 666’s gravity can deflect light passing by it. Often the light from a background galaxy gets deformed into an arc around the lens galaxy, and sometimes what’s called an Einstein ring. In this case, the ring is formed mainly by two lensed images of the background galaxy. The size, shape and brightness of the Einstein ring depends on the distribution of mass throughout the foreground lensing galaxy.

Vegetti and her team obtained extra sharp near-infrared image of JVAS B1938 + 666 by using the 10-meter Keck II telescope and its adaptive optics system, which corrects for the blurring effects of Earth’s atmosphere, and provides stunningly sharp images. With these data, they neatly determined the mass distribution of JVAS B1938 + 666 as well as the shape and brightness of the background galaxy.

The researchers used a sophisticated numerical technique to derive a model of the lens galaxy’s mass, as well as to map any excess lens mass that could not be accounted for by the galaxy. What they found was an excess mass near the Einstein ring that they attributed to the presence of a satellite, or “dwarf,” galaxy. Vegetti’s team also used a separate analytical model to test the detected excess mass. They found that a satellite galaxy is indeed required to explain the data.

“This satellite galaxy is exciting because it was detected in the excess-mass map despite its low mass,” commented Robert Schmidt of the Center for Astronomy at Heidelberg University, in a related Nature article. “A natural question to ask is whether the satellite galaxy can be observed directly rather than by its gravitational effect on the shape of a background object. With current instrumentation, the answer is no. The object is simply too distant to be imaged directly. But the message here is that it is possible to spot these elusive objects around distant lens galaxies without knowing where to look for them.”

Galaxies like our own are believed to form over billions of years through the merging of many smaller galaxies. So it’s expected that there should be many smaller dwarf galaxies buzzing around the Milky Way. However, very few of these tiny relic galaxies have been observed which has led astronomers to conclude that many of them must have very few stars or possibly may be made almost exclusively of dark matter.

Scientists theorize the existence of dark matter to explain observations that suggest there is far more mass in the universe than can be seen. However, because the particles that make up dark matter do not absorb or emit light, they have so far proven impossible to detect and identify. Computer modeling suggests that the Milky Way should have about 10,000 satellite dwarf galaxies, but only 30 have been observed.

“It could be that many of the satellite galaxies are made of dark matter, making them elusive to detect, or there may be a problem with the way we think galaxies form”, says Vegetti.

In the new study, Vegetti worked with Prof. Leon Koopmans of the University of Groningen, Netherlands; Dr. David Lagattuta and Prof. Christopher Fassnacht of the University of California at Davis; Dr. Matthew Auger of the University of California at Santa Barbara; and Dr. John McKean of the Netherlands Institute for Radio Astronomy.

“The existence of this low-mass dark galaxy is just within the bounds we expect if the Universe is composed of dark matter which has a low temperature. However, further dark satellites will need to be found to confirm this conclusion,” says Vegetti.

The W. M. Keck Observatory operates two 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Big Island of Hawaii. The twin telescopes feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system which cancels out much of the interference caused by Earth’s turbulent atmosphere. The Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

Adapted from a MIT press release.

For more information please visit

Gaseous ring around young star raises questions

Astronomers have detected a mysterious ring of carbon monoxide gas around the young star V1052 Cen, which is about 700 light years away in the southern constellation Centaurus. The ring is part of the star’s planet-forming disk, and it’s as far from V1052 Cen as Earth is from the sun. Discovered with the European Southern Observatory's Very Large Telescope, its edges are uniquely crisp.

Artist's conception image of a young star surrounded by a disk
(made up of rings)
Credits: NASA/JPL-Caltech

Carbon monoxide is often detected near young stars, but the gas is usually spread through the planet-forming disk. What’s different about this ring is that it is shaped more like a rope than a dinner plate, said Charles Cowley, professor emeritus in the University of Michigan who led the international research effort.

“It’s exciting because this is the most constrained ring we've ever seen, and it requires an explanation,” Cowley said. “At present time, we just don't understand what makes it a rope rather than a dish.” Perhaps magnetic fields hold it in place, the researchers say. Maybe “shepherding planets” are reining it in like several of Saturn’s moons control certain planetary rings.

“What makes this star so special is its very strong magnetic field and the fact that it rotates extremely slow compared to other stars of the same type,” said Swetlana Hubrig, of the Leibniz Institute for Astrophysics Potsdam (AIP), Germany.

The star’s unique properties first caught the researchers’ attention in 2008, and they have been studying it intensely ever since.

Understanding the interaction between central stars, their magnetic fields, and planet-forming disks is crucial for astronomers to reconstruct the solar system's history. It is also important to account for the diversity of the known planetary systems beyond our own. This new finding raises more questions than it answers about the late stages of star and solar system formation.

“Why do turbulent motions not tear the ring apart?” Cowley wondered. “How permanent is the structure? What forces might act to preserve it for times comparable to the stellar formation time itself?”

The team is excited to have found an ideal test case to study this type of object.

“This star is a gift of nature,” Hubrig said.

The findings are newly published online in Astronomy and Astrophysics. The paper is titled “The narrow, inner CO ring around the magnetic Herbig Ae star HD 101412.” Authors are from the University of Michigan, the Leibniz Institute for Astrophysics Potsdam (AIP) in Germany, the Istituto Nazionale die Astrofisica in Italy and the European Southern Observatory.

Contact University of Michigan
Nicole Casal Moore, ncmoore@umich.edu, +1 734 647-7087

Science contact
Dr. Swetlana Hubrig, shubrig@aip.de, +49 331-7499-225

Press contact
Dr. Gabriele Schönherr / Kerstin Mork, presse@aip.de ,Tel.: +49 331 7499 469

The key topics of the Leibniz Institute for Astrophysics are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP is a foundation according to civil law and is a member of the Leibniz Association. The Leibniz Association is a network of 87 independent research institutes and scientific service facilities, which strive for scientific solutions for major social challenges.

Tuesday, January 17, 2012

A New View of an Icon

Combining almost opposite ends of the electromagnetic spectrum, this composite of the Herschel in far-infrared and XMM-Newton’s X-ray images shows how the hot young stars detected by the X-ray observations are sculpting and interacting with the surrounding ultra-cool gas and dust, which, at only a few degrees above absolute zero, is the critical material for star formation itself. Both wavelengths would be blocked by Earth’s atmosphere, so are critical to our understanding of the lifecycle of stars

Credits: far-infrared: ESA/Herschel/PACS/SPIRE/Hill, Motte, HOBYS Key Programme Consortium; X-ray: ESA/XMM-Newton/EPIC/XMM-Newton-SOC/Boulanger.

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The Eagle Nebula as never seen before. In 1995, the Hubble Space Telescope's 'Pillars of Creation' image of the Eagle Nebula became one of the most iconic images of the 20th century. Now, two of ESA's orbiting observatories have shed new light on this enigmatic star-forming region.

The Eagle Nebula is 6500 light-years away in the constellation of Serpens. It contains a young hot star cluster, NGC6611, visible with modest back-garden telescopes, that is sculpting and illuminating the surrounding gas and dust, resulting in a huge hollowed-out cavity and pillars, each several light-years long.

The Hubble image hinted at new stars being born within the pillars, deeply inside small clumps known as 'evaporating gaseous globules' or EGGs. Owing to obscuring dust, Hubble's visible light picture was unable to see inside and prove that young stars were indeed forming.

This 1995 Hubble Space Telescope image of the ‘Pillars of Creation’ is probably the most famous astronomical image of the 20th Century. Taken in visible light using a combination of SII/H-alpha and OIII filters, it shows a part of the Eagle Nebula where new stars are forming. The tallest pillar is around 4 light-years high.

Credits: NASA/ESA/STScI, Hester & Scowen (Arizona State University)
HI-RES JPEG (Size: 814 kb)

The ESA Herschel Space Observatory's new image shows the pillars and the wide field of gas and dust around them. Captured in far-infrared wavelengths, the image allows astronomers to see inside the pillars and structures in the region.

In parallel, a new multi-energy X-ray image from ESA's XMM-Newton telescope shows those hot young stars responsible for carving the pillars.

XMM-Newton’s images of the Eagle Nebula region in X-rays, which here is colour-coded to show different energy levels (red: 0.3–1 keV, green: 1–2 keV and blue: 2–8 keV) is helping astronomers to investigate a theory that the Eagle Nebula is being powered by a hidden supernova remnant. The researchers are looking for signs of very diffuse emission and how far this extends around the region. They believe that an absence of this X-ray emission beyond that found by previous orbiting space telescopes (Chandra and Spitzer) would support the supernova remnant theory. The work on this is continuing.

Credits: ESA/XMM-Newton/EPIC/XMM-Newton-SOC/Boulanger

Combining the new space data with near-infrared images from the European Southern Observatory's (ESO's) Very Large Telescope at Paranal, Chile, and visible-light data from its Max Planck Gesellschaft 2.2m diameter telescope at La Silla, Chile, we see this iconic region of the sky in a uniquely beautiful and revealing way.

Messier 16 is a diffuse emission nebula that contains the young open cluster NGC6611. The iconic ‘Pillars of Creation’ image taken with the Hubble Space Telescope in 1995 is captured in near-infrared by the VLT, which penetrates straight through the obscuring gas and dust, rendering them almost invisible. The pillars are only a small portion of the extensive nebulous region imaged in far-infrared by ESA’s Herschel Space Observatory, which shows cool dust and gas tendrils being carved away by the hot stars seen in the X-ray image from XMM-Newton. The wide-field optical image from the ESO MPG telescope puts the pillars into context against the full scale of the nebula, which is over 75 light-years across.

Credits: far-infrared: ESA/Herschel/PACS/SPIRE/Hill, Motte, HOBYS Key Programme Consortium; ESA/XMM-Newton/EPIC/XMM-Newton-SOC/Boulanger; optical: MPG/ESO; near-infrared/VLT/ISAAC/McCaughrean & Andersen/AIP/ESO.

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In visible wavelengths, the nebula shines mainly due to reflected starlight and hot gas filling the giant cavity, covering the surfaces of the pillars and other dusty structures.

A movie of the Eagle Nebula at several wavelengths. A high-resolution downloadable version of the movie is available for download (19mb) in Quicktime format. Credits: far-infrared: ESA/Herschel/PACS/SPIRE/Hill, Motte, HOBYS Key Programme Consortium; ESA/XMM-Newton/EPIC/XMM-Newton-SOC/Boulanger; optical: MPG/ESO; near-infrared/VLT/ISAAC/McCaughrean & Andersen/AIP/ESO.

At near-infrared wavelengths, the dust becomes almost transparent and the pillars practically vanish.

The 8.2m-diameter VLT’s ANTU telescope imaged the famous Pillars of Creation region and its surroundings in near-infrared using the ISAAC instrument. This enabled astronomers to penetrate the obscuring dust in their search to detect newly formed stars. The research into the ‘evaporating gaseous globules’ (EGGs), which were first detected in the Hubble images, needed the near-infrared capabilities and resolution of the VLT to peel back the layers of dust and detect the low-mass young stars cocooned within the EGG shells. The near-infrared results showed that 11 of the 73 EGGs detected possibly contained stars, and that the tips of the pillars contain stars and nebulosity not seen in the Hubble image.

Credits: VLT/ISAAC/McCaughrean & Andersen/AIP/ESO . HI-RES JPEG (Size:
996 kb)

In far-infrared, Herschel detects this cold dust and the pillars reappear, this time glowing in their own light.

Intricate tendrils of dust and gas are seen to shine, giving astronomers clues about how it interacts with strong ultraviolet light from the hot stars seen by XMM-Newton.

In 2001, Very Large Telescope near-infrared images had shown only a small minority of the EGGs were likely to contain stars being born.

However, Herschel's image makes it possible to search for young stars over a much wider region and thus come to a much fuller understanding of the creative and destructive forces inside the Eagle Nebula.

This Herschel image of the Eagle Nebula, colour coded to 70 microns for blue and 160 microns for green using the PACS (Photodetector Array Camera) and 250 microns for red using the SPIRE (Spectral and Photometric Imaging Receiver) shows the self-emission of the intensely cold nebula’s gas and dust as never seen before. Each colour shows a different temperature of dust, from around 10 degrees above absolute zero (10K) for the red, up to around 40K for the blue. In the far–infrared, the nebula shows its intricate tendril nature, with vast cavities forming an almost cave-like surrounding to the famous pillars, which take on an ethereal ghostly appearance. The gas and dust provide the material for the star formation that is still under way inside this enigmatic nebula .

Credits: ESA/Herschel/PACS/SPIRE/Hill, Motte, HOBYS Key Programme Consortium. HI-RES JPEG (Size:
423 kb)

Earlier mid-infrared images from ESA's Infrared Space Observatory and NASA's Spitzer, and the new XMM-Newton data, have led astronomers to suspect that one of the massive, hot stars in NGC6611 may have exploded in a supernova 6000 years ago, emitting a shockwave that destroyed the pillars.

However, because of the distance of the Eagle Nebula, we won't see this happen for several hundred years yet.

Up to 1998 the ESA ISO (Infrared Space Observatory) was the most sensitive mid infrared telescope ever built. ISO observations were performed at 7 microns (and 15 microns, not shown) aiming to detect embedded sources in the pillars.

Credits: ESA/ISO/Pilbratt et al. HI-RES JPEG (Size:
192 kb)

Powerful ground-based telescopes continue to provide astonishing views of our Universe, but images in far-infrared, mid-infrared and X-ray wavelengths are impossible to obtain owing to the absorbing effects of Earth's atmosphere.

Space-based observatories such as ESA's Herschel and XMM-Newton help to peel back that veil and see the full beauty of the Universe across the electromagnetic spectrum.

With regions like the Eagle Nebula, combining all of these observations helps astronomers to understand the complex yet amazing lifecycle of stars.

NASA's Fermi Space Telescope Explores New Energy Extremes

New sources emerge and old sources fade as the LAT's view extends into higher energies. Credit: NASA/DOE/Fermi LAT Collaboration and A. Neronov et al. View larger

Fermi's view of the gamma-ray sky continually improves. This image of the entire sky includes three years of observations by Fermi's Large Area Telescope (LAT). It shows how the sky appears at energies greater than 1 billion electron volts (1 GeV). Brighter colors indicate brighter gamma-ray sources. A diffuse glow fills the sky and is brightest along the plane of our galaxy (middle). Discrete gamma-ray sources include pulsars and supernova remnants within our galaxy as well as distant galaxies powered by supermassive black holes. Credit: NASA/DOE/Fermi LAT Collaboration. View larger

This all-sky Fermi view includes only sources with energies greater than 10 GeV. From some of these sources, Fermi's LAT detects only one gamma-ray photon every four months. Brighter colors indicate brighter gamma-ray sources. Credit: NASA/DOE/Fermi LAT Collaboration. View larger

Fermi's Large Area Telescope (LAT) scans the entire sky every three hours, continually deepening its portrait of the sky in gamma rays, the most energetic form of light. While the energy of visible light falls between about 2 and 3 electron volts, the LAT detects gamma rays with energies ranging from 20 million to more than 300 billion electron volts (GeV).

At higher energies, gamma rays are rare. Above 10 GeV, even Fermi's LAT detects only one gamma ray every four months.

Before Fermi, we knew of only four discrete sources above 10 GeV, all of them pulsars," said David Thompson, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md. "With the LAT, we've found hundreds, and we're showing for the first time just how diverse the sky is at these high energies."

Any object producing gamma rays at these energies is undergoing extraordinary astrophysical processes. More than half of the 496 sources in the new census are active galaxies, where matter falling into a supermassive black hole powers jets that spray out particles at nearly the speed of light.

Only about 10 percent of the known sources lie within our own galaxy. They include rapidly rotating neutron stars called pulsars, the expanding debris from supernova explosions, and in a few cases, binary systems containing massive stars.

More than a third of the sources are completely unknown, having no identified counterpart detected in other parts of the spectrum. With the new catalog, astronomers will be able to compare the behavior of different sources across a wider span of gamma-ray energies for the first time.

Just as bright infrared sources may fade to invisibility in the ultraviolet, some of the gamma-ray sources above 1 GeV vanish completely when viewed at higher, or "harder," energies.

One example is the well-known radio galaxy NGC 1275, which is a bright, isolated source below 10 GeV. At higher energies it fades appreciably and another nearby source begins to appear. Above 100 GeV, NGC 1275 becomes undetectable by Fermi, while the new source, the radio galaxy IC 310, shines brightly.

The Fermi hard-source list is the product of an international team led by Pascal Fortin at the Ecole Polytechnique's Laboratoire Leprince-Ringuet in Palaiseau, France, and David Paneque at the Max Planck Institute for Physics in Munich.

The catalog serves as an important roadmap for ground-based facilities called Atmospheric Cherenkov Telescopes, which have amassed about 130 gamma-ray sources with energies above 100 GeV. They include the Major Atmospheric Gamma Imaging Cherenkov telescope (MAGIC) on La Palma in the Canary Islands, the Very Energetic Radiation Imaging Telescope Array System (VERITAS) in Arizona, and the High Energy Stereoscopic System (H.E.S.S.) in Namibia.

"Our catalog will have a significant impact on ground-based facilities' work by pointing them to the most likely places to find gamma-ray sources emitting above 100 GeV," Paneque said.

Compared to Fermi's LAT, these ground-based observatories have much smaller fields of view. They also make fewer observations because they cannot operate during daytime, bad weather or a full moon.

More than half of the sources above 10 GeV are black-hole-powered active galaxies. More than a third of the sources are completely unknown, having no identified counterpart detected in other parts of the spectrum. Credit: NASA's Goddard Space Flight Center. View larger

"As Fermi's exposure constantly improves our view of hard sources, ground-based telescopes are becoming more sensitive to lower-energy gamma rays, allowing us to bridge these two energy regimes," Fortin added.

NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership. Fermi is managed by Goddard. It was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Related Links:

For images related to this story

Very Energetic Radiation Imaging Telescope Array System (VERITAS) in Arizona

High Energy Stereoscopic System (H.E.S.S.) in Namibia

Trent J. Perrotto
Headquarters, Washington

Sunday, January 15, 2012

Hubble Spots a Busy Barred Spiral

NGC 3259
Credit: ESA/Hubble & NASA

This classic shot of a galaxy in the constellation of Ursa Major was taken by the NASA/ESA Hubble Space Telescope. NGC 3259 is a bright barred spiral galaxy located approximately 110 million light-years from Earth.

Being a fully-formed active galaxy, its bright central bulge hosts a supermassive black hole, whose huge appetite for matter explains the high luminosity of the galaxy’s core: as it devours its surroundings, the black hole emits intense radiation across the whole electromagnetic spectrum, including in visible light.

The beautiful spiral arms of the galaxy are not left out either as they contain dark lanes of dust and gas, ideal spawning grounds for stars. These bright, young, hot stars appear in rich clusters in the galaxy’s arms and are what gives the galaxy its blueish hue.

Interestingly, the galaxy has a small companion (visible to the left of the image), a much smaller galaxy that may be orbiting NGC 3259. In the background, numerous distant galaxies can be seen, easily identifiable by their elliptical shapes. They are visible here mainly in infrared light, which is shown in red in this image.