Saturday, June 30, 2012

Cassini Finds Likely Subsurface Ocean on Saturn Moon

This artist's concept shows a possible scenario for the internal structure of Titan, as suggested by data from NASA's Cassini spacecraft. Scientists have been trying to determine what is under Titan's organic-rich atmosphere and icy crust. Image credit: A. Tavani. Full image and caption

Squeezing and Stretching Titan
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PASADENA, Calif. -- Data from NASA's Cassini spacecraft have revealed Saturn's moon Titan likely harbors a layer of liquid water under its ice shell.

Researchers saw a large amount of squeezing and stretching as the moon orbited Saturn. They deduced that if Titan were composed entirely of stiff rock, the gravitational attraction of Saturn would cause bulges, or solid "tides," on the moon only 3 feet (1 meter) in height. Spacecraft data show Saturn creates solid tides approximately 30 feet (10 meters) in height, which suggests Titan is not made entirely of solid rocky material. The finding appears in today's edition of the journal Science.

"Cassini's detection of large tides on Titan leads to the almost inescapable conclusion that there is a hidden ocean at depth," said Luciano Iess, the paper's lead author and a Cassini team member at the Sapienza University of Rome, Italy. "The search for water is an important goal in solar system exploration, and now we've spotted another place where it is abundant."

Titan takes only 16 days to orbit Saturn, and scientists were able to study the moon's shape at different parts of its orbit. Because Titan is not spherical, but slightly elongated like a football, its long axis grew when it was closer to Saturn. Eight days later, when Titan was farther from Saturn, it became less elongated and more nearly round. Cassini measured the gravitational effect of that squeeze and pull.

Scientists were not sure Cassini would be able to detect the bulges caused by Saturn's pull on Titan. By studying six close flybys of Titan from Feb. 27, 2006, to Feb. 18, 2011, researchers were able to determine the moon's internal structure by measuring variations in the gravitational pull of Titan using data returned to NASA's Deep Space Network (DSN).

"We were making ultrasensitive measurements, and thankfully Cassini and the DSN were able to maintain a very stable link," said Sami Asmar, a Cassini team member at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The tides on Titan pulled up by Saturn aren't huge compared to the pull the biggest planet, Jupiter, has on some of its moons. But, short of being able to drill on Titan's surface, the gravity measurements provide the best data we have of Titan's internal structure."

An ocean layer does not have to be huge or deep to create these tides. A liquid layer between the external, deformable shell and a solid mantle would enable Titan to bulge and compress as it orbits Saturn. Because Titan's surface is mostly made of water ice, which is abundant in moons of the outer solar system, scientists infer Titan's ocean is likely mostly liquid water.

On Earth, tides result from the gravitational attraction of the moon and sun pulling on our surface oceans. In the open oceans, those can be as high as two feet (60 centimeters). While water is easier to move, the gravitational pulling by the sun and moon also causes Earth's crust to bulge in solid tides of about 20 inches (50 centimeters).

The presence of a subsurface layer of liquid water at Titan is not itself an indicator for life. Scientists think life is more likely to arise when liquid water is in contact with rock, and these measurements cannot tell whether the ocean bottom is made up of rock or ice. The results have a bigger implication for the mystery of methane replenishment on Titan.

"The presence of a liquid water layer in Titan is important because we want to understand how methane is stored in Titan's interior and how it may outgas to the surface," said Jonathan Lunine, a Cassini team member at Cornell University, Ithaca, N.Y. "This is important because everything that is unique about Titan derives from the presence of abundant methane, yet the methane in the atmosphere is unstable and will be destroyed on geologically short timescales."

A liquid water ocean, "salted" with ammonia, could produce buoyant ammonia-water liquids that bubble up through the crust and liberate methane from the ice. Such an ocean could serve also as a deep reservoir for storing methane.

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. DSN, also managed by JPL, is an international network of antennas that supports interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions. Cassini's radio science team is based at Wellesley College in Massachusetts. JPL is a division of the California Institute of Technology in Pasadena.

For more information about the mission, visit: and .

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

Dwayne Brown 202-358-1726
NASA Headquarters, Washington

Friday, June 29, 2012

IGR J11014-6103: Has the Speediest Pulsar Been Found?

IGR J11014-6103
Credit: X-ray: NASA/CXC/UC Berkeley/J.Tomsick et al & ESA/XMM-Newton, Optical: DSS; IR: 2MASS/UMass/IPAC-Caltech/NASA/NSF

Researchers using three different telescopes -- NASA's Chandra X-ray Observatory and ESA's XMM-Newton in space, and the Parkes radio telescope in Australia -- may have found the fastest moving pulsar ever seen.

The evidence for this potentially record-breaking speed comes, in part, from the features highlighted in this composite image. X-ray observations from Chandra (green) and XMM-Newton (purple) have been combined with infrared data from the 2MASS project and optical data from the Digitized Sky Survey (colored red, green and blue, but appearing in the image as white).

The large area of diffuse X-rays seen by XMM-Newton was produced when a massive star exploded as a supernova, leaving behind a debris field, or supernova remnant known as SNR MSH 11-16A. Shocks waves from the supernova have heated surrounding gas to several million degrees Kelvin, causing the remnant to glow brightly in X-rays.

The Chandra image shown in the inset ("Chandra Close-up") reveals a comet-shaped X-ray source well outside the boundary of the supernova remnant. This source consists of a point-like object with a long tail trailing behind it for about 3 light years. The bright star nearby and also the one in SNR MSH11-16A are both likely to be foreground stars unrelated to the supernova remnant.

The point-like X-ray source was discovered by the International Gamma-Ray Astrophysics Laboratory, or INTEGRAL, and is called IGR J11014-6103 (or IGR J11014 for short). It may be a rapidly spinning, super-dense star (known as a "pulsar", a type of neutron star) that was ejected during the explosion. If so, it is racing away from the center of the supernova remnant at millions of miles per hour.

The favored interpretation for the tail of X-ray emission is that a pulsar wind nebula, that is, a "wind" of high-energy particles produced by the pulsar, has been swept behind a bow shock created by the pulsar's high speed. (A similar case was seen in another object known as PSR B1957+20 .

The elongated emission is pointing towards the center of MSH 11-61A where the pulsar would have been formed, supporting the idea that the Chandra image is of a pulsar wind nebula and its bow shock. Another interesting feature of the Chandra image, also seen with XMM-Newton, is the faint X-ray tail extending to the top-right. The cause of this feature is unknown, but similar tails have been seen from other pulsars that also do not line up with the pulsar's direction of motion.

Based on earlier observations, astronomers estimate that the age of MSH 11-61A, as it appears in the image, is approximately 15,000 years, and it lies at a distance of about 30,000 light years away from Earth. Combining these values with the distance that the pulsar has appeared to have traveled from the center of the MSH 11-61A, astronomers estimate that IGR J11014 is moving at a speed between 5.4 million and 6.5 million miles per hour.

The only other neutron star associated with a supernova remnant that may rival this in speed is the candidate found in the supernova remnant known as G350.1-0.3. The speed of the neutron star candidate in this system is estimated to lie between 3 and 6 million miles per hour.

The high speeds estimated for both IGR J11014 and the neutron star candidate in G350.1-0.3 are preliminary and need to be confirmed. If they are confirmed, explaining the high speeds of the neutron star presents a severe challenge to existing models for supernova explosions.

One important caveat in the conclusion that IGR J11014 may be the fastest moving pulsar is that pulsations have not been detected in it during a search with the Commonwealth Scientific and Industrial Research Organization (CSIRO) Parkes radio telescope. This non-detection is not surprising for a pulsar located about 30,000 light years away.

However, there are other pieces of evidence that support the pulsar interpretation. First, the lack of detection of a counterpart to the X-ray source in optical or infrared images supports the idea that it is a pulsar, since such objects are very faint at these wavelengths. Also, there are no apparent differences in the brightness of the source between XMM-Newton observations in 2003 and the Chandra observations in 2011, behavior that is expected if IGR J11014 is a pulsar. Finally, the X-ray spectrum of the source, that is, its signature in energy, is similar to what astronomers expect to see for a pulsar.

These results were published in the May 10, 2012 issue of The Astrophysical Journal Letters. The authors were John Tomsick and Arash Bodaghee (University of California, Berkeley), Jerome Rodriguez and Sylvain Chaty (University of Paris, CEA Saclay), Fernando Camilo (Columbia University), Francesca Fornasini (UC Berkeley), and Farhid Rahoui (Harvard-Smithsonian Center for Astrophysics).

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

Fast Facts for IGR J11014-6103:

Scale: 1 degree across (~576 light years)
Category: Supernovas & Supernova Remnants, Neutron Stars/X-ray Binaries
Coordinates (J2000): RA 11h 01m 22.08s | Dec -61° 03' 25.20"
Constellation: Carina
Observation Date: 6 Sep 2011
Observation Time: 1 hours 23 min.
Obs. ID: 12420
Color Code: X-ray-Chandra: (Green) X-ray-XMM: (Purple); Optical (Red, Green, Blue)
Instrument: ACIS
References: Tomsick, J et al, 2012 ApJ 750:39; arXiv:1204.2836
Distance Estimate: About 30,000 light years

Thursday, June 28, 2012

Hubble, Swift Detect First-Ever Changes in an Exoplanet Atmosphere

Exoplanet HD 189733b (Artist's Illustration)
Science Credit:NASA,ESA, A. Lecavelier des Etangs (CNRS-UMPC, France), and P. Wheatley (University of Warwick)

WASHINGTON — An international team of astronomers using data from NASA's Hubble Space Telescope has made an unparalleled observation, detecting significant changes in the atmosphere of a planet located beyond our solar system.

The scientists conclude the atmospheric variations occurred in response to a powerful eruption on the planet's host star, an event observed by NASA's Swift satellite.

"The multiwavelength coverage by Hubble and Swift has given us an unprecedented view of the interaction between a flare on an active star and the atmosphere of a giant planet," said lead researcher Alain Lecavelier des Etangs at the Paris Institute of Astrophysics (IAP), part of the French National Scientific Research Center located at Pierre and Marie Curie University in Paris.

The exoplanet is HD 189733b, a gas giant similar to Jupiter, but about 14 percent larger and more massive. The planet circles its star at a distance of only 3 million miles, or about 30 times closer than Earth's distance from the Sun, and completes an orbit every 2.2 days. Its star, named HD 189733A, is about 80 percent the size and mass of our Sun.

Astronomers classify the planet as a "hot Jupiter." Previous Hubble observations show that the planet's deep atmosphere reaches a temperature of about 1,900 degrees Fahrenheit (1,030 degrees Celsius).

HD 189733b periodically passes across, or transits, its parent star, and these events give astronomers an opportunity to probe its atmosphere and environment. In a previous study, a group led by Lecavelier des Etangs used Hubble to show that hydrogen gas was escaping from the planet's upper atmosphere. The finding made HD 189733b only the second known "evaporating" exoplanet at the time.

The system is just 63 light-years away, so close that its star can be seen with binoculars near the famous Dumbbell Nebula. This makes HD 189733b an ideal target for studying the processes that drive atmospheric escape.

"Astronomers have been debating the details of atmospheric evaporation for years, and studying HD 189733b is our best opportunity for understanding the process," said Vincent Bourrier, a doctoral student at IAP and a team member on the new study.

When HD 189733b transits its star, some of the star's light passes through the planet's atmosphere. This interaction imprints information on the composition and motion of the planet's atmosphere into the star's light.

In April 2010, the researchers observed a single transit using Hubble's Space Telescope Imaging Spectrograph (STIS), but they detected no trace of the planet's atmosphere. Follow-up STIS observations in September 2011 showed a surprising reversal, with striking evidence that a plume of gas was streaming away from the exoplanet.

The researchers determined that at least 1,000 tons of gas was leaving the planet's atmosphere every second. The hydrogen atoms were racing away at speeds greater than 300,000 miles per hour. The findings will appear in an upcoming issue of the journal Astronomy & Astrophysics.

Because X-rays and extreme ultraviolet starlight heat the planet's atmosphere and likely drive its escape, the team also monitored the star with Swift's X-ray Telescope (XRT). On Sept. 7, 2011, just eight hours before Hubble was scheduled to observe the transit, Swift was monitoring the star when it unleashed a powerful flare. It brightened by 3.6 times in X-rays, a spike occurring atop emission levels that already were greater than the Sun's.

"The planet's close proximity to the star means it was struck by a blast of X-rays tens of thousands of times stronger than the Earth suffers even during an X-class solar flare, the strongest category," said co-author Peter Wheatley, a physicist at the University of Warwick in England.

After accounting for the planet's enormous size, the team notes that HD 189733b encountered about 3 million times as many X-rays as Earth receives from a solar flare at the threshold of the X class.

Hubble is a project of international cooperation between NASA and the European Space Agency. Swift is operated in collaboration with several U.S. institutions and partners in the United Kingdom, Italy, Germany, and Japan. NASA's Goddard Space Flight Center in Greenbelt, Md., manages both missions.

For images and video related to this finding, visit:

For more information about Swift, visit:

For more information about Hubble, visit:


J. D. Harrington
Headquarters, Washington

Lynn Chandler
NASA Goddard Space Flight Center, Greenbelt, Md.

Wednesday, June 27, 2012

New Way of Probing Exoplanet Atmospheres

PR Image eso1227a
Artist’s impression of the exoplanet Tau Boötis b

PR Image eso1227b
The parent star of the famous exoplanet Tau Boötis b

PR Image eso1227c
Wide-field view of the parent star of the famous exoplanet Tau Boötis b


PR Video eso1227a
Artist’s impression of the famous exoplanet Tau Boötis b

PR Video eso1227b
Zooming in on the star Tau Boötis

Tau Boötis b revealed

For the first time a clever new technique has allowed astronomers to study the atmosphere of an exoplanet in detail — even though it does not pass in front of its parent star. An international team has used ESO’s Very Large Telescope to directly catch the faint glow from the planet Tau Boötis b. They have studied the planet’s atmosphere and measured its orbit and mass precisely for the first time — in the process solving a 15-year old problem. Surprisingly, the team also finds that the planet’s atmosphere seems to be cooler higher up, the opposite of what was expected. The results will be published in the 28 June 2012 issue of the journal Nature.

The planet Tau Boötis b [1] was one of the first exoplanets to be discovered back in 1996, and it is still one of the closest exoplanets known. Although its parent star is easily visible with the naked eye, the planet itself certainly is not, and up to now it could only be detected by its gravitational effects on the star. Tau Boötis b is a large “hot Jupiter” planet orbiting very close to its parent star.

Like most exoplanets, this planet does not transit the disc of its star (like the recent transit of Venus). Up to now such transits were essential to allow the study of hot Jupiter atmospheres: when a planet passes in front of its star it imprints the properties of the atmosphere onto the starlight. As no starlight shines through Tau Boötis b’s atmosphere towards us, this means the planet’s atmosphere could not be studied before.

But now, after 15 years of attempting to study the faint glow that is emitted from hot Jupiter exoplanets, astronomers have finally succeeded in reliably probing the structure of the atmosphere of Tau Boötis b and deducing its mass accurately for the first time. The team used the CRIRES [2] instrument on the Very Large Telescope (VLT) at ESO’s Paranal Observatory in Chile. They combined high quality infrared observations (at wavelengths around 2.3 microns) [3] with a clever new trick to tease out the weak signal of the planet from the much stronger one from the parent star [4].

Lead author of the study Matteo Brogi (Leiden Observatory, the Netherlands) explains: “Thanks to the high quality observations provided by the VLT and CRIRES we were able to study the spectrum of the system in much more detail than has been possible before. Only about 0.01% of the light we see comes from the planet, and the rest from the star, so this was not easy”.

The majority of planets around other stars were discovered by their gravitational effects on their parent stars, which limits the information that can be gleaned about their mass: they only allow a lower limit to be calculated for a planet’s mass [5]. The new technique pioneered here is much more powerful. Seeing the planet’s light directly has allowed the astronomers to measure the angle of the planet’s orbit and hence work out its mass precisely. By tracing the changes in the planet’s motion as it orbits its star, the team has determined reliably for the first time that Tau Boötis b orbits its host star at an angle of 44 degrees and has a mass six times that of the planet Jupiter in our own Solar System.

“The new VLT observations solve the 15-year old problem of the mass of Tau Boötis b. And the new technique also means that we can now study the atmospheres of exoplanets that don’t transit their stars, as well as measuring their masses accurately, which was impossible before”, says Ignas Snellen (Leiden Observatory, the Netherlands), co-author of the paper. “This is a big step forward.”

As well as detecting the glow of the atmosphere and measuring Tau Boötis b’s mass, the team has probed its atmosphere and measured the amount of carbon monoxide present, as well as the temperature at different altitudes by means of a comparison between the observations and theoretical models. A surprising result from this work was that the new observations indicated an atmosphere with a temperature that falls higher up. This result is the exact opposite of the temperature inversion — an increase in temperature with height — found for other hot Jupiter exoplanets [6] [7].

The VLT observations show that high resolution spectroscopy from ground-based telescopes is a valuable tool for a detailed analysis of non-transiting exoplanets’ atmospheres. The detection of different molecules in future will allow astronomers to learn more about the planet’s atmospheric conditions. By making measurements along the planet’s orbit, astronomers may even be able to track atmospheric changes between the planet’s morning and evening.

"This study shows the enormous potential of current and future ground-based telescopes, such as the E-ELT. Maybe one day we may even find evidence for biological activity on Earth-like planets in this way”, concludes Ignas Snellen.


[1] The name of the planet, Tau Boötis b, combines the name of the star (Tau Boötis, or τ Bootis, τ is the Greek letter “tau”, not a letter “t” ) with the letter “b” indicating that this is the first planet found around this star. The designation Tau Boötis a is used for the star itself.

[2] CRyogenic InfraRed Echelle Spectrometer

[3] At infrared wavelengths, the parent star emits less light than in the optical regime, so this is a wavelength regime favorable for separating out the dim planet’s signal.

[4] This method uses the velocity of the planet in orbit around its parent star to distinguish its radiation from that of the star and also from features coming from the Earth’s atmosphere. The same team of astronomers tested this technique before on a transiting planet, measuring its orbital velocity during its crossing of the stellar disc.

[5] This is because the tilt of the orbit is normally unknown. If the planet’s orbit is tilted relative to the line of sight between Earth and the star then a more massive planet causes the same observed back and forth motion of the star as a lighter planet in a less tilted orbit and it is not possible to separate the two effects.

[6] Thermal inversions are thought to be characterised by molecular features in emission in the spectrum, rather than in absorption, as interpreted from photometric observations of hot Jupiters with the Spitzer Space Telescope. The exoplanet HD209458b is the best-studied example of thermal inversions in the exoplanet atmospheres.

[7] This observation supports models in which strong ultraviolet emission associated to chromospheric activity — similar to the one exhibited by the host star of Tau Boötis b — is responsible for the inhibition of the thermal inversion.

More information

This research was presented in a paper "The signature of orbital motion from the dayside of the planet τ Boötis b" to appear in the journal Nature on 28 June 2012.

The team is composed of Matteo Brogi (Leiden Observatory, the Netherlands), Ignas A. G. Snellen (Leiden Observatory), Remco J. de Kok (SRON, Utrecht, the Netherlands), Simon Albrecht (Massachusetts Institute of Technology, Cambridge, USA), Jayne Birkby (Leiden Observatory) and Ernst J. W. de Mooij (University of Toronto, Canada; Leiden Observatory).

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”.

Research paper in Nature
Photos of the VLT
Other images taken with the VLT


Ignas Snellen
Leiden Observatory, Leiden University
Leiden, The Netherlands
Tel: +31 715 275838

Matteo Brogi
Leiden Observatory, Leiden University
Leiden, The Neherlands
Tel: +31 715 278434

Jayne Birkby
Leiden Observatory, Leiden University
Leiden, The Netherlands
Tel: +31 715 275832

Richard Hook
ESO, La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591

Remco de Kok
Space Research Organization Netherlands (SRON)
Utrecht, The Netherlands
Tel: +31 88 777 5725

Gas Cloud Will Collide with our Galaxy’s Black Hole in 2013

Images taken over the last decade using the NACO instrument on ESO’s Very Large Telescope show the motion of a cloud of gas that is falling towards the supermassive black hole at the centre of the Milky Way. This is the first time ever that the approach of such a doomed cloud to a supermassive black hole has been observed and it is expected to break up completely during 2013. Credit: ESO/MPE

Scientists have determined a giant gas cloud is on a collision course with the black hole in the center of our galaxy, and the two will be close enough by mid-2013 to provide a unique opportunity to observe how a super massive black hole sucks in material, in real time. This will give astronomers more information on how matter behaves near a black hole.

“The next few years will be really fantastic and exciting because we are probing new territory,” said Reinhard Genzel, leading a team from the ESO in observations with the Very Large Telescope. “Here this cloud comes in gets disrupted and now it will begin to interact with the hot gas right around the black hole. We have never seen this before.”

By June of 2012, the gas cloud is expected to be just 36 light-hours (equivalent to 40,000,000,000 km) away from our galaxy’s black hole, which is extremely close in astronomical terms.

Astronomers have determined the speed of the gas cloud has increased, doubling over the past seven years, and is now reaching more than 8 million km per hour. The cloud is estimated to be three times the mass of Earth and the density of the cloud is much higher than that of the hot gas surrounding black hole. But the black hole has a tremendous gravitational force, and so the gas cloud will fall into the direction of the black hole, be elongated and stretched and look like spaghetti, said Stefan Gillessen, astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Munich, Germany, who has been observing our galaxy’s black hole, known as Sagittarius A* (or Sgr A*), for 20 years.

“So far there were only two stars that came that close to Sagittarius A*,” Gillessen said. “They passed unharmed, but this time will be different: the gas cloud will be completely ripped apart by the tidal forces of the black hole.”

Watch a video of observations of the cloud for the past 10 years:

No one really knows how the collision will unfold, but the cloud’s edges have already started to shred and it is expected to break up completely over the coming months. As the time of actual collision approaches, the cloud is expected to get much hotter and will probably start to emit X-rays as a result of the interaction with the black hole.

Although direct observations of black holes are impossible, as they do not emit light or matter, astronomers can identify a black hole indirectly due to the gravitational forces observed in their vicinity.

A black hole is what remains after a super massive star dies. When the “fuel” of a star runs low, it will first swell and then collapse to a dense core. If this remnant core has more than three times the mass of our Sun, it will transform to a black hole. So-called super massive black holes are the largest type of black holes, as their mass equals hundreds of thousands to a billion times the mass of our Sun.

Black holes are thought to be at the center of all galaxies, but their origin is not fully understood and astrophysicists can only speculate as to what happens inside them. And so this upcoming collision just 27,000 light years away will likely provide new insights on the behavior of black holes.

by Nancy Atkinson - Universe Today

Tuesday, June 26, 2012

NASA's Hubble Spots Rare Gravitational Arc from Distant, Hefty Galaxy Cluster

IDCS J1426.5+3508
Credit: NASA, ESA, and A. Gonzalez (University of Florida, Gainesville), A. Stanford (University of California, Davis and Lawrence Livermore National Laboratory), and M. Brodwin (University of Missouri-Kansas City and Harvard-Smithsonian Center for Astrophysics)

Seeing is believing, except when you don't believe what you see.

Astronomers using NASA's Hubble Space Telescope have found a puzzling arc of light behind an extremely massive cluster of galaxies residing 10 billion light-years away. The galactic grouping, discovered by NASA's Spitzer Space Telescope, was observed when the universe was roughly a quarter of its current age of 13.7 billion years. The giant arc is the stretched shape of a more distant galaxy whose light is distorted by the monster cluster's powerful gravity, an effect called gravitational lensing.

The trouble is, the arc shouldn't exist.

"When I first saw it, I kept staring at it, thinking it would go away," said study leader Anthony Gonzalez of the University of Florida in Gainesville. "According to a statistical analysis, arcs should be extremely rare at that distance. At that early epoch, the expectation is that there are not enough galaxies behind the cluster bright enough to be seen, even if they were 'lensed' or distorted by the cluster. The other problem is that galaxy clusters become less massive the farther back in time you go. So it's more difficult to find a cluster with enough mass to be a good lens for gravitationally bending the light from a distant galaxy."

Galaxy clusters are collections of hundreds to thousands of galaxies bound together by gravity. They are the most massive structures in our universe. Astronomers frequently study galaxy clusters to look for faraway, magnified galaxies behind them that would otherwise be too dim to see with telescopes. Many such gravitationally lensed galaxies have been found behind galaxy clusters closer to Earth.

The surprise in this Hubble observation is spotting a galaxy lensed by an extremely distant cluster. Dubbed IDCS J1426.5+3508, the cluster is the most massive found at that epoch, weighing as much as 500 trillion suns. It is 5 to 10 times larger than other clusters found at such an early time in the universe's history. The team spotted the cluster in a search using NASA's Spitzer Space Telescope in combination with archival optical images taken as part of the National Optical Astronomy Observatory's Deep Wide Field Survey at the Kitt Peak National Observatory, Tucson, Ariz. The combined images allowed them to see the cluster as a grouping of very red galaxies, indicating they are far away.

This unique system constitutes the most distant cluster known to "host" a giant gravitationally lensed arc. Finding this ancient gravitational arc may yield insight into how, during the first moments after the big bang, conditions were set up for the growth of hefty clusters in the early universe.

The arc was spotted in optical images of the cluster taken in 2010 by Hubble's Advanced Camera for Surveys. The infrared capabilities of Hubble's Wide Field Camera 3 (WFC3) helped provide a precise distance, confirming it to be one of the farthest clusters yet discovered.

Once the astronomers determined the cluster's distance, they used Hubble, the Combined Array for Research in Millimeter-wave Astronomy (CARMA) radio telescope, and NASA's Chandra X-ray Observatory to independently show that the galactic grouping is extremely massive.

CARMA helped the astronomers determine the cluster's mass by measuring how primordial light from the big bang was affected as it passed through the extremely hot, tenuous gas that permeates the grouping. The astronomers then used the WFC3 observations to map the cluster's mass by calculating how much cluster mass was needed to produce the gravitational arc. Chandra data, which revealed the cluster's brightness in X-rays, was also used to measure the cluster's mass.

"The chance of finding such a gigantic cluster so early in the universe was less than one percent in the small area we surveyed," said team member Mark Brodwin of the University of Missouri-Kansas City. "It shares an evolutionary path with some of the most massive clusters we see today, including the Coma Cluster and the recently discovered El Gordo Cluster."

An analysis of the arc revealed that the lensed object is a star-forming galaxy that existed 10 billion to 13 billion years ago. The team hopes to use Hubble again to obtain a more accurate distance to the lensed galaxy.

Gonzalez has considered several possible explanations for the arc.

One explanation is that distant galaxy clusters, unlike nearby clusters, have denser concentrations of galaxies at their cores, making them better magnifying glasses. However, even if the distant cores were denser, the added bulk still should not provide enough gravitational muscle to produce the giant arc seen in Gonzalez's observations, according to a statistical analysis.

Another possibility is that the initial microscopic fluctuations in matter made right after the big bang were different from those predicted by standard cosmological simulations, and therefore produced more massive clusters than expected.

"I'm not yet convinced by any of these explanations," Gonzalez said. "After all, we have found only one example. We really need to study more extremely massive galaxy clusters that existed between 8 billion and 10 billion years ago to see how many more gravitationally lensed objects we can find."

The team's results are described in three papers, which will appear online today and will be published in the July 10, 2012, issue of The Astrophysical Journal. Gonzalez is the first author on one of the papers; Brodwin, on another; and Adam Stanford of the University of California at Davis, on the third.


Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514 /

Anthony Gonzalez
University of Florida, Gainesville, Fla.
352-392-2052 x233

Source: HubbleSite

Radio Galaxies in the Distant Universe

A small section from a Hubble image of distant galaxies. A new paper has detected and studied infrared counterparts to all the galaxies in the main image with strong radio emission, the first time such a complete sample has been obtained. Credit: NASA/Hubble. Low Resolution Image (jpg)

For over a decade astronomers have been probing a region of the northern sky, not far from the handle of the Big Dipper, that is relatively free of bright stars and the diffuse glow of the Milky Way. The scientists want to take advantage of the clarity of the sky there to peer beyond our galaxy to study remote galaxies in the distant universe. This region, about half the angular size of the full moon, is now known to have over 50,000 galaxies.

CfA astronomers Steve Willner, Matt Ashby, and Jia-Sheng Huang and their colleagues studied the region using the SAO-led Infrared Array Camera (IRAC) on the Spitzer Space Telescope. Surveys have detected 1122 galaxies in this region that emit strongly at radio wavelengths, a consequence of their undergoing active star formation or of hosting active supermassive black holes at their nuclei. Since the radio observations alone are unable to estimate the distances to the galaxies or unravel the precise mechanisms powering their emission, the team undertook to use infrared data to provide that information.

In a paper to appear in the Astrophysical Journal, the team reports that it has detected essentially 100% of the radio galaxies in their infrared images. This is the first sample of the deep sky that has been able to completely associate radio galaxies with infrared counterparts, and it means that the conclusions they reach will be much more reliable. The team finds that 10-15% of the galaxies, most of them within a few billion light-years of us, are undergoing bursts of star formation. Roughly another quarter of the galaxies have supermassive black holes that are actively accreting matter; this group lies at greater distances (light from the most distant ones has been traveling for over eleven billion years). The remainder of the galaxies are still of uncertain nature, but now that both radio and infrared observations are available for all of them, future follow-up studies will have a strong basis for proceeding.

Monday, June 25, 2012

Cassini Shows Why Jet Streams Cross-Cut Saturn

A particularly strong jet stream churns through Saturn's northern hemisphere in this false-color view from NASA's Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI. Full image and caption

This figure examines a particularly strong jet stream and the eddies that drive it through the atmosphere of Saturn's northern hemisphere. Data from NASA's Cassini spacecraft were used to create this figure. Image Credit: NASA/JPL-Caltech/SSI

Turbulent jet streams, regions where winds blow faster than in other places, churn east and west across Saturn. Scientists have been trying to understand for years the mechanism that drives these wavy structures in Saturn's atmosphere and the source from which the jets derive their energy.

In a new study appearing in the June edition of the journal Icarus, scientists used images collected over several years by NASA's Cassini spacecraft to discover that the heat from within the planet powers the jet streams. Condensation of water from Saturn's internal heating led to temperature differences in the atmosphere. The temperature differences created eddies, or disturbances that move air back and forth at the same latitude, and those eddies, in turn, accelerated the jet streams like rotating gears driving a conveyor belt.

A competing theory had assumed that the energy for the temperature differences came from the sun. That is how it works in the Earth's atmosphere.

"We know the atmospheres of planets such as Saturn and Jupiter can get their energy from only two places: the sun or the internal heating. The challenge has been coming up with ways to use the data so that we can tell the difference," said Tony Del Genio of NASA's Goddard Institute for Space Studies, N.Y., the lead author of the paper and a member of the Cassini imaging team.

The new study was possible in part because Cassini has been in orbit around Saturn long enough to obtain the large number of observations required to see subtle patterns emerge from the day-to-day variations in weather. "Understanding what drives the meteorology on Saturn, and in general on gaseous planets, has been one of our cardinal goals since the inception of the Cassini mission," said Carolyn Porco, imaging team lead, based at the Space Science Institute, Boulder, Colo. "It is very gratifying to see that we're finally coming to understand those atmospheric processes that make Earth similar to, and also different from, other planets."

Rather than having a thin atmosphere and solid-and-liquid surface like Earth, Saturn is a gas giant whose deep atmosphere is layered with multiple cloud decks at high altitudes. A series of jet streams slice across the face of Saturn visible to the human eye and also at altitudes detectable to the near-infrared filters of Cassini's cameras. While most blow eastward, some blow westward. Jet streams occur on Saturn in places where the temperature varies significantly from one latitude to another.

Thanks to the filters on Cassini's cameras, which can see near-infrared light reflected to space, scientists now have observed the Saturn jet stream process for the first time at two different, low altitudes. One filtered view shows the upper part of the troposphere, a high layer of the atmosphere where Cassini sees thick, high-altitude hazes and where heating by the sun is strong. Views through another filter capture images deeper down, at the tops of ammonia ice clouds, where solar heating is weak but closer to where weather originates. This is where water condenses and makes clouds and rain.

In the new study, which is a follow-up to results published in 2007, the authors used automated cloud tracking software to analyze the movements and speeds of clouds seen in hundreds of Cassini images from 2005 through 2012.

"With our improved tracking algorithm, we've been able to extract nearly 120,000 wind vectors from 560 images, giving us an unprecedented picture of Saturn's wind flow at two independent altitudes on a global scale," said co-author and imaging team associate John Barbara, also at the Goddard Institute for Space Studies. The team's findings provide an observational test for existing models that scientists use to study the mechanisms that power the jet streams.

By seeing for the first time how these eddies accelerate the jet streams at two different altitudes, scientists found the eddies were weak at the higher altitudes where previous researchers had found that most of the sun's heating occurs. The eddies were stronger deeper in the atmosphere. Thus, the authors could discount heating from the sun and infer instead that the internal heat of the planet is ultimately driving the acceleration of the jet streams, not the sun. The mechanism that best matched the observations would involve internal heat from the planet stirring up water vapor from Saturn's interior. That water vapor condenses in some places as air rises and releases heat as it makes clouds and rain. This heat provides the energy to create the eddies that drive the jet streams.

The condensation of water was not actually observed; most of that process occurs at lower altitudes not visible to Cassini. But the condensation in mid-latitude storms does happen on both Saturn and Earth. Storms on Earth - the low- and high-pressure centers on weather maps - are driven mainly by the sun's heating and do not mainly occur because of the condensation of water, Del Genio said. On Saturn, the condensation heating is the main driver of the storms, and the sun's heating is not important.

Images of one of the strongest jet streams and a figure from the paper can be found at , and .

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute in Boulder, Colo.

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

Joe Mason 720-974-5859
Space Science Institute, Boulder, Colo.

Bill Steigerwald/Nancy Neal Jones 301-286-5017/6-0039
Goddard Space Flight Center, Greenbelt, Md. /

Friday, June 22, 2012

Multiple Mergers Generate Ultraluminous Infrared Galaxy

A team of astronomers led by Professor Yoshiaki Taniguchi (Ehime University) has concluded that the ultraluminous infrared galaxy (ULIRG) Arp 220 (Figure 1) developed from a multiple merger among four or more galaxies. Their new imaging data from the Subaru Telescope and optical spectroscopy from the W. M. Keck Observatory revealed two tidal tails that facilitated their analysis of Arp 220's development. Because Arp 220 is an archetypal or representative ULIRG, the team's findings facilitate an understanding of ULIRG development in general.

Figure 1: Optical images of Arp 220
Left: Image from the Hubble Space Telescope’s Advanced Camera for Surveys (ACS). (Credit: Hubble Space Telescope)
Right: Image from the Subaru Prime Focus Camera (Suprime-Cam). Huge, complex tidal remnants surround Arp 220. (Credit: Ehime University / NAOJ)

First discovered from the Infrared Astronomical Satellite's (IRAS) all-sky survey in the mid-1980s, ULIRGs are the most luminous class of galaxies in the relatively near or local Universe. Most of their energy output is in the infrared, suggesting that they contain a large amount of dust, an indication of immense star formation.

Astronomers have proposed different scenarios for the development of ULIRGs. Since ULIRGs' huge infrared luminosities (1012 Lsun), powered mostly by a large number of massive stars, are comparable to the high luminosity of quasars, the brightest class of active galactic nuclei, a 1988 scenario (Note 1) proposed that ULIRGs were an intermediate phase in the evolution of quasars after a merger. Another scenario proposed by Professor Taniguchi and his associate in 1998 (Note 2) hypothesized that multiple mergers among several galaxies explained the observational properties. However, a number of questions remained unanswered: 1) How many galaxies were merged into one? and 2) Which types of galaxies were merged into one? Since then, explanations for the origins of ULIRGs have remained controversial. The current team conducted research to help answer these questions and to propose a plausible, data-based explanation for the origin of ULIRGs.

The team made detailed optical imaging observations of Arp 220 using FOCAS (Faint Object Camera and Spectrograph) on the Subaru Telescope and the LRIS (Low Resolution Imaging Spectometer) on the Keck II Telescope. The new imaging data revealed a spectacular pair of tidal tails extending more than 50,000 light years. Intermediate-mass stars (with masses a few to several times that of the Sun), the remains of intense star formation events called "starbursts", dominate the composition of the tidal tails. The presence of an Hα absorption line (Figure 2) led to the first detection of these features. Dr. Kazuya Matsubayashi said, "I was very surprised when I found these Hα absorption features in the two tidal tails."

Figure 2: Images of Arp 220
Left: Hα image taken with the Faint Object Camera and Spectrograph (FOCAS) mounted on the Subaru Telescope. The dark parts in the figure (Hα absorption) pointed out with arrows are three post-starburst regions. Right: For reference, an R band image from Suprime-Cam. (Credit: Ehime University / NAOJ)

What could explain these surprising features? A merger between two galaxies is necessary to cause a starburst in a merging system. Therefore, two post-starburst galaxies could have produced the two long tidal tails. However, four galaxies are needed to generate the two post-starburst galaxies (Figure 3). The post-starburst tidal tails revealed by the new observations suggest a new scenario for the merging history in Arp 220. The team suggests that the two observed tidal tails in Arp 220 need a merger between two advanced (i.e., post-starburst) merger remnants. In sum, four spiral galaxies are necessary to explain the observed post-starburst tidal tails in Arp 220. They conclude that Arp 220 comes from a multiple merger that includes at least four galaxies, not from a typical merger. The team thinks that this conclusion about Arp 220 can be applied to other galaxy groups.

Figure 3: The proposed scenario of multiple mergers for Arp 220
Each pair of spiral galaxies merges into one, resulting in two merged starburst galaxies. As time goes by (200 million years after merging or longer), these galaxies evolve into post-starburst galaxies, which then merge again, resulting in the current Arp 220 with a pair of post-starburst tidal tails. (Credit: Ehime University / NAOJ)

There are a significant number of compact groups of galaxies in the Universe that could lead to multiple mergers. Professor Taniguchi noted, "Some of such compact groups have already merged into one. They are the ULIRGs observed to date." Some galaxies are associated together in a single gravitationally-bound group, and they will inevitably merge into one galaxy within several billion years.

Although ULIRGs are thought to evolve into quasars and then into giant early-type galaxies, future considerations of the evolution of galaxies will need to take into account the impact of multiple mergers, not just major mergers between two galaxies. Professor Taniguchi applied this principle to the fate of our Milky Way Galaxy: "Very recently, NASA announced that our Milky Way Galaxy will merge with the Andromeda Galaxy (M31) into a giant elliptical galaxy within several billion years. Please don't worry. That would only be a merger between two galaxies, so our Milky Way will not evolve into a ULIRG."


These results will be published in The Astrophysical Journal, Volume 753, July 10, 2012.


1. Sanders, D. B., et al. 1988, ApJ, 325, 74
2. Taniguchi, Y., & Shioya, Y. 1998, ApJ, 501, L167

Thursday, June 21, 2012

Planetrise: Alien World Looms Large in its Neighbor's Sky

In this artist's conception, a "hot Neptune" known as Kepler-36c looms in the sky of its neighbor, the rocky world Kepler-36b. The two planets have repeated close encounters, experiencing a conjunction every 97 days on average. At that time, they are separated by less than 5 Earth-Moon distances. Such close approaches stir up tremendous gravitational tides that squeeze and stretch both planets, which may promote active volcanism on Kepler-36b. Credit: David A. Aguilar (CfA).

over the horizon. Now imagine that instead of the Moon, a gas giant planet spanning three times more sky loomed over the molten landscape of a lava world. This alien vista exists in the newly discovered two-planet system of Kepler-36.

"These two worlds are having close encounters," said Josh Carter, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics (CfA).

"They are the closest to each other of any planetary system we've found," added co-author Eric Agol of the University of Washington.

Carter, Agol and their colleagues report their discovery in the June 21st Science Express.

They spotted the planets in data from NASA's Kepler spacecraft, which can detect a planet when it passes in front of, and briefly reduces the light coming from, its parent star.

The newfound system contains two planets circling a subgiant star much like the Sun except several billion years older. The inner world, Kepler-36b, is a rocky planet 1.5 times the size of Earth and weighing 4.5 times as much. It orbits about every 14 days at an average distance of less than 11 million miles.

The outer world, Kepler-36c, is a gaseous planet 3.7 times the size of Earth and weighing 8 times as much. This "hot Neptune" orbits once each 16 days at a distance of 12 million miles.

The two planets experience a conjunction every 97 days on average. At that time, they are separated by less than 5 Earth-Moon distances. Since Kepler-36c is much larger than the Moon, it presents a spectacular view in its neighbor's sky. (Coincidentally, the smaller Kepler-36b would appear about the size of the Moon when viewed from Kepler-36c.) Such close approaches stir up tremendous gravitational tides that squeeze and stretch both planets.

Researchers are struggling to understand how these two very different worlds ended up in such close orbits. Within our solar system, rocky planets reside close to the Sun while the gas giants remain distant.

Although Kepler-36 is the first planetary system found to experience such close encounters, it undoubtedly won't be the last.

"We're wondering how many more like this are out there," said Agol.

"We found this one on a first quick look," added Carter. "We're now combing through the Kepler data to try to locate more."

This result was made possible with asteroseismology. Asteroseismology is the study of stars by observing their natural oscillations. Sunlike stars resonate like musical instruments, due to sound waves trapped in their interiors. And just like a musical instrument, the larger the star, the "deeper" are its resonances. This trapped sound makes the stars gently breathe in and out, or oscillate.

Co-author Bill Chaplin (University of Birmingham, UK) noted, "Kepler-36 shows beautiful oscillations. By measuring the oscillations we were able to measure the size, mass and age of the star to exquisite precision."

He added, "Without asteroseismology, it would not have been possible to place such tight constraints on the properties of the planets."

The research was funded by NASA, the Space Telescope Science Institute and the National Science Foundation.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

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

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics

Wednesday, June 20, 2012

VLT Takes a Close Look at NGC 6357

PR Image eso1226a
Close-up view of NGC 6357

PR Image eso1226b
The stellar nursery NGC 6357 in the constellation of Scorpius

PR Image eso1226c
Wide-field view of the area of NGC 6357


PR Video eso1226a
Zooming in on NGC 6357

PR Video eso1226b
Panning across the stellar nursery NGC 6357

ESO’s Very Large Telescope (VLT) has taken the most detailed image so far of a spectacular part of the stellar nursery called NGC 6357. The view shows many hot young stars, glowing clouds of gas and weird dust formations sculpted by ultraviolet radiation and stellar winds.

Deep in the Milky Way in the constellation of Scorpius (The Scorpion) lies NGC 6357 [1], a region of space where new stars are being born in of chaotic clouds of gas and dust [2]. The outer parts of this vast nebula have now been imaged by ESO’s Very Large Telescope, producing the best picture of this region taken so far [3].

The new picture shows a broad river of dust across the centre that absorbs the light from more distant objects. To the right there is a small cluster of brilliant blue-white young stars that have formed from the gas. These are probably only a few million years old, very young by stellar standards. The intense ultraviolet radiation streaming out from these stars is hollowing out a cavity in the surrounding gas and dust and sculpting it in strange ways.

The whole image is covered with dark trails of cosmic dust, but some of the most fascinating dark features appear at the lower right and on the right hand edge of the picture. Here the radiation from the bright young stars has created curious elephant trunk columns, similar to the famous “pillars of creation” in the Eagle Nebula (opo9544a). Cosmic dust is much finer than the more familiar domestic variety. It more closely resembles smoke and consists mostly of tiny particles of silicates, graphite, and water ice that were produced and expelled into space by earlier generations of stars.

The bright central part of NGC 6357 contains a cluster of high-mass stars whose inhabitants are among the brightest in our galaxy. This inner region, not seen in this new picture, has been much studied and imaged by the NASA/ESA Hubble Space Telescope (heic0619). But this new picture shows that even the less well known outer parts of this nursery contain fascinating structures that can be revealed by the power of the VLT.

This image was produced as part of the ESO Cosmic Gems programme [4].


[1] This object also bears the curious name War and Peace Nebula, which has no link to Tolstoy’s great novel, but was given to this object by scientists working on the Midcourse Space Experiment. They noted that the bright, western part of the nebula resembled a dove, while the eastern part looked like a skull in their infrared images. Unfortunately this effect cannot be seen in the visible-light image presented here. The object is also occasionally nicknamed the Lobster Nebula.

[2] NGC 6357 was first recorded visually by John Herschel from South Africa in 1837. He only recorded the brightest central parts and the full scale of this huge nebula was only seen in photographs much later.

[3] The part of NGC 6357 shown in the new VLT image has not been targeted by the NASA/ESA Hubble Space Telescope.

[4] The ESO Cosmic Gems programme is an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of small amounts of observing time, combined with otherwise unused time on the telescopes’ schedules so as to minimise the impact on science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

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 the VLT
Other images taken with the VLT


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

Tuesday, June 19, 2012

Most Quasars Live on Snacks, Not Large Meals

The Homes of Quasars
Credit:NASA,ESA, and K. Schawinski (Yale University)
Release Images

Black holes in the early universe needed a few snacks rather than one giant meal to fuel their quasars and help them grow, a new study shows.

Quasars are the brilliant beacons of light that are powered by black holes feasting on captured material, and in the process, heating some of the matter to millions of degrees. The brightest quasars reside in galaxies distorted by collisions with other galaxies. These encounters send lots of gas and dust into the gravitational whirlpool of hungry black holes.

Now, however, astronomers are uncovering an underlying population of fainter quasars that thrive in normal-looking spiral galaxies. They are triggered by black holes snacking on such tasty treats as a batch of gas or the occasional small satellite galaxy.

A census of 30 quasar host galaxies conducted with two of NASA's premier observatories, the Hubble Space Telescope and Spitzer Space Telescope, has found that 26 of the host galaxies bear no tell-tale signs of collisions with neighbors, such as distorted shapes. Only one galaxy in the sample shows evidence of an interaction with another galaxy. The galaxies existed roughly 8 billion to 12 billion years ago, during a peak epoch of black-hole growth.

The study, led by Kevin Schawinski of Yale University, bolsters evidence that the growth of most massive black holes in the early universe was fueled by small, long-term events rather than dramatic short-term major mergers.

"Quasars that are products of galaxy collisions are very bright," Schawinski said. "The objects we looked at in this study are the more typical quasars. They're a lot less luminous. The brilliant quasars born of galaxy mergers get all the attention because they are so bright and their host galaxies are so messed up. But the typical bread-and-butter quasars are actually where most of the black-hole growth is happening. They are the norm, and they don't need the drama of a collision to shine."

Schawinski's science paper has been accepted for publication in a letter to the Monthly Notices of the Royal Astronomical Society.

For his analysis, Schawinski analyzed galaxies observed by the Spitzer and Hubble telescopes in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). He chose 30 dust-enshrouded galaxies that appeared extremely bright in infrared images taken by the Spitzer telescope, a sign that their resident black holes are feasting on infalling material. The dust is blocking the quasar's light at visible wavelengths. But infrared light pierces the dust, allowing Schawinski to study the galaxies' detailed structure. The masses of those galaxies are comparable to our Milky Way's.

Schawinski then studied the galaxies in near-infrared images taken by Hubble's Wide Field Camera 3. Hubble's sharp images allowed careful analysis of galaxy shapes, which would be significantly distorted if major galaxy mergers had taken place and were disrupting the structure. Instead, in all but one instance, the galaxies show no such disruption.

Whatever process is stoking the quasars, it's below the detection capability of even Hubble. "I think it's a combination of processes, such as random stirring of gas, supernovae blasts, swallowing of small bodies, and streams of gas and stars feeding material into the nucleus," Schawinski said.

A black hole doesn't need much gas to satisfy its hunger and turn on a quasar. "There's more than enough gas within a few light-years from the center of our Milky Way to turn it into a quasar," Schawinski explained. "It just doesn't happen. But it could happen if one of those small clouds of gas ran into the black hole. Random motions and stirrings inside the galaxy would channel gas into the black hole. Ten billion years ago, those random motions were more common and there was more gas to go around. Small galaxies also were more abundant and were swallowed up by larger galaxies."

The galaxies in Schawinski's study are prime targets for the James Webb Space Telescope, a large infrared observatory scheduled to launch later this decade. "To get to the heart of what kinds of events are powering the quasars in these galaxies, we need the Webb telescope. Hubble and Spitzer have been the trailblazers for finding them."

The team of astronomers in this study consists of K. Schawinski, B.D. Simmons, C.M. Urry, and E. Glikman (Yale University), and E. Treister (Universidad de Concepción, Chile).


Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514 /

Kevin Schawinski
Yale University, New Haven, Conn.

Globular Cluster M10

Credit: ESA/Hubble & NASA

Like many of the most famous objects in the sky, globular cluster Messier 10 was of little interest to its discoverer: Charles Messier, the 18th century French astronomer, catalogued over 100 galaxies and clusters, but was primarily interested in comets. Through the telescopes available at the time, comets, nebulae, globular clusters and galaxies appeared just as faint, diffuse blobs and could easily be confused for one another.

Only by carefully observing their motion — or lack of it — were astronomers able to distinguish them: comets move slowly relative to the stars in the background, while other more distant astronomical objects do not move at all.

Messier’s decision to catalogue all the objects that he could find and that were not comets, was a pragmatic solution which would have a huge impact on astronomy. His catalogue of just over 100 objects includes many of the most famous objects in the night sky. Messier 10, seen here in an image from the NASA/ESA Hubble Space Telescope, is one of them. Messier described it in the very first edition of his catalogue, which was published in 1774 and included the first 45 objects he identified.

Messier 10 is a ball of stars that lies about 15 000 light-years from Earth, in the constellation of Ophiuchus (The Serpent Bearer). Approximately 80 light-years across, it should therefore appear about two thirds the size of the Moon in the night sky. However, its outer regions are extremely diffuse, and even the comparatively bright core is too dim to see with the naked eye.

Hubble, which has no problems seeing faint objects, has observed the brightest part of the centre of the cluster in this image, a region which is about 13 light-years across.

This image is made up of observations made in visible and infrared light using Hubble’s Advanced Camera for Surveys. The observations were carried out as part of a major Hubble survey of globular clusters in the Milky Way.

A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant flashenthunder. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition has now closed and the results will be published soon.

Source: ESA/Hubble  - Space Telescope