Giant Asteroid Vesta Likely Cold and Dark Enough for Ice

The south pole of the giant asteroid Vesta, as imaged by the framing camera on NASA's Dawn spacecraft in September 2011. (Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Though generally thought to be quite dry, roughly half of the giant asteroid Vesta is expected to be so cold and to receive so little sunlight that water ice could have survived there for billions of years, according to the first published models of Vesta's average global temperatures and illumination by the sun.

"Near the north and south poles, the conditions appear to be favorable for water ice to exist beneath the surface," says Timothy Stubbs of NASA's Goddard Space Flight Center in Greenbelt, Md., and the University of Maryland, Baltimore County. Stubbs and Yongli Wang of the Goddard Planetary Heliophysics Institute at the University of Maryland published the models in the January 2012 issue of the journal Icarus. The models are based on information from telescopes including NASA's Hubble Space Telescope.

Vesta, the second-most massive object in the asteroid belt between Mars and Jupiter, probably does not have any significant permanently shadowed craters where water ice could stay frozen on the surface all the time, not even in the roughly 300-mile-diameter (480-kilometer-diameter) crater near the south pole, the authors note. The asteroid isn't a good candidate for permanent shadowing because it is tilted on its axis at about 27 degrees, which is even greater than Earth's tilt of roughly 23 degrees. In contrast, the moon, which does have permanently shadowed craters, is tilted at only about 1.5 degrees. As a result of its large tilt, Vesta has seasons, and every part of the surface is expected to see the sun at some point during Vesta's year.

The presence or absence of water ice on Vesta tells scientists something about the tiny world's formation and evolution, its history of bombardment by comets and other objects, and its interaction with the space environment. Because similar processes are common to many other planetary bodies, including the moon, Mercury and other asteroids, learning more about these processes has fundamental implications for our understanding of the solar system as a whole. This kind of water ice is also potentially valuable as a resource for further exploration of the solar system.

Though temperatures on Vesta fluctuate during the year, the model predicts that the average annual temperature near Vesta's north and south poles is less than roughly minus 200 degrees Fahrenheit (145 kelvins). That is the critical average temperature below which water ice is thought to be able to survive in the top 10 feet or so (few meters) of the soil, which is called regolith.

Near Vesta's equator, however, the average yearly temperature is roughly minus 190 degrees Fahrenheit (150 kelvins), according to the new results. Based on previous modeling, that is expected to be high enough to prevent water from remaining within a few meters of the surface. This band of relatively warm temperatures extends from the equator to about 27 degrees north and south in latitude.

"On average, it's colder at Vesta's poles than near its equator, so in that sense, they are good places to sustain water ice," says Stubbs. "But they also see sunlight for long periods of time during the summer seasons, which isn't so good for sustaining ice. So if water ice exists in those regions, it may be buried beneath a relatively deep layer of dry regolith."

The modeling also indicates that relatively small surface features, such as craters measuring around 6 miles (10 kilometers) in diameter, could significantly affect the survival of water ice. "The bottoms of some craters could be cold enough on average -- about 100 kelvins -- for water to be able to survive on the surface for much of the Vestan year [about 3.6 years on Earth]," Stubbs explains. "Although, at some point during the summer, enough sunlight would shine in to make the water leave the surface and either be lost or perhaps redeposit somewhere else."

So far, Earth-based observations suggest that the surface of Vesta is quite dry. However, the Dawn spacecraft is getting a much closer view. Dawn is investigating the role of water in the evolution of planets by studying Vesta and Ceres, two bodies in the asteroid belt that are considered remnant protoplanets -- baby planets whose growth was interrupted when Jupiter formed.

Dawn is looking for water using the gamma ray and neutron detector (GRaND) spectrometer, which can identify hydrogen-rich deposits that could be associated with water ice. The spacecraft recently entered a low orbit that is well suited to collecting gamma ray and neutron data.

"Our perceptions of Vesta have been transformed in a few months as the Dawn spacecraft has entered orbit and spiraled closer to its surface," says Lucy McFadden, a planetary scientist at NASA Goddard and a Dawn mission co-investigator. "More importantly, our new views of Vesta tell us about the early processes of solar system formation. If we can detect evidence for water beneath the surface, the next question will be is it very old or very young, and that would be exciting to ponder."

The modeling done by Stubbs and Wang, for example, relies on information about Vesta's shape. Before Dawn, the best source of that information was a set of images taken by NASA's Hubble Space Telescope in 1994 and 1996. But now, Dawn and its camera are getting a much closer view of Vesta.

"The Dawn mission gives researchers a rare opportunity to observe Vesta for an extended period of time, the equivalent of about one season on Vesta," says Stubbs. "Hopefully, we'll know in the next few months whether the GRaND spectrometer sees evidence for water ice in Vesta's regolith. This is an important and exciting time in planetary exploration."

Dawn's mission to Vesta and Ceres is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Va., designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team. The asteroid modeling by Stubbs and Wang is an extension of analysis originally applied to the moon and partially funded by the NASA Lunar Science Institute.

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Giant flakes make graphene oxide gel: Discovery could boost metamaterials, high-strength fibers

ScienceDaily (Oct. 20, 2011) — Giant flakes of graphene oxide in water aggregate like a stack of pancakes, but infinitely thinner, and in the process gain characteristics that materials scientists may find delicious.

A new paper by scientists at Rice University and the University of Colorado details how slices of graphene, the single-atom form of carbon, in a solution arrange themselves to form a nematic liquid crystal in which particles are free-floating but aligned.

That much was already known. The new twist is that if the flakes -- in this case, graphene oxide -- are big enough and concentrated enough, they retain their alignment as they form a gel. That gel is a handy precursor for manufacturing metamaterials or fibers with unique mechanical and electronic properties.

The team reported its discovery online this week in the Royal Society of Chemistry journal Soft Matter. Rice authors include Matteo Pasquali, a professor of chemical and biomolecular engineering and of chemistry; James Tour, the T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science; postdoctoral research associate Dmitry Kosynkin; and graduate students Budhadipta Dan and Natnael Behabtu. Ivan Smalyukh, an assistant professor of physics at the University of Colorado at Boulder, led research for his group, in which Dan served as a visiting scientist.

"Graphene materials and fluid phases are a great research area," Pasquali said. "From the fundamental point of view, fluid phases comprising flakes are relatively unexplored, and certainly so when the flakes have important electronic properties.

"From the application standpoint, graphene and graphene oxide can be important building blocks in such areas as flexible electronics and conductive and high-strength materials, and can serve as templates for ordering plasmonic structures," he said.

By "giant," the researchers referred to irregular flakes of graphene oxide up to 10,000 times as wide as they are high. (That's still impossibly small: on average, roughly 12 microns wide and less than a nanometer high.) Previous studies showed smaller bits of pristine graphene suspended in acid would form a liquid crystal and that graphene oxide would do likewise in other solutions, including water.

This time the team discovered that if the flakes are big enough and concentrated enough, the solution becomes semisolid. When they constrained the gel to a thin pipette and evaporated some of the water, the graphene oxide flakes got closer to each other and stacked up spontaneously, although imperfectly.

"The exciting part for me is the spontaneous ordering of graphene oxide into a liquid crystal, which nobody had observed before," said Behabtu, a member of Pasquali's lab. "It's still a liquid, but it's ordered. That's useful to make fibers, but it could also induce order on other particles like nanorods."

He said it would be a simple matter to heat the concentrated gel and extrude it into something like carbon fiber, with enhanced properties provided by "mix-ins."

Testing the possibilities, the researchers mixed gold microtriangles and glass microrods into the solution, and found both were effectively forced to line up with the pancaking flakes. Their inclusion also helped the team get visual confirmation of the flakes' orientation.

The process offers the possibility of the large-scale ordering and alignment of such plasmonic particles as gold, silver and palladium nanorods, important components in optoelectronic devices and metamaterials, they reported.

Behabtu added that heating the gel "crosslinks the flakes, and that's good for mechanical strength. You can even heat graphene oxide enough to reduce it, stripping out the oxygen and turning it back into graphite."

Co-authors of the paper are Angel Martinez and Julian Evans, graduate students of Smalyukh at the University of Colorado at Boulder.

The Institute for Complex Adaptive Matter, the Colorado Renewable and Sustainable Energy Initiative, the National Science Foundation, the Air Force Research Lab, the Air Force Office of Scientific Research, the Welch Foundation, the U.S. Army Corps of Engineers Environmental Quality and Installation Program and M-I Swaco supported the research.

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Budhadipta Dan, Natnael Behabtu, Angel Martinez, Julian S. Evans, Dmitry V. Kosynkin, James M. Tour, Matteo Pasquali, Ivan I. Smalyukh. Liquid crystals of aqueous, giant graphene oxide flakes. Soft Matter, 2011; DOI: 10.1039/C1SM06418E

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Giant flakes make graphene oxide gel: Discovery could boost metamaterials, high-strength fibers

ScienceDaily (Oct. 20, 2011) — Giant flakes of graphene oxide in water aggregate like a stack of pancakes, but infinitely thinner, and in the process gain characteristics that materials scientists may find delicious.

A new paper by scientists at Rice University and the University of Colorado details how slices of graphene, the single-atom form of carbon, in a solution arrange themselves to form a nematic liquid crystal in which particles are free-floating but aligned.

That much was already known. The new twist is that if the flakes -- in this case, graphene oxide -- are big enough and concentrated enough, they retain their alignment as they form a gel. That gel is a handy precursor for manufacturing metamaterials or fibers with unique mechanical and electronic properties.

The team reported its discovery online this week in the Royal Society of Chemistry journal Soft Matter. Rice authors include Matteo Pasquali, a professor of chemical and biomolecular engineering and of chemistry; James Tour, the T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science; postdoctoral research associate Dmitry Kosynkin; and graduate students Budhadipta Dan and Natnael Behabtu. Ivan Smalyukh, an assistant professor of physics at the University of Colorado at Boulder, led research for his group, in which Dan served as a visiting scientist.

"Graphene materials and fluid phases are a great research area," Pasquali said. "From the fundamental point of view, fluid phases comprising flakes are relatively unexplored, and certainly so when the flakes have important electronic properties.

"From the application standpoint, graphene and graphene oxide can be important building blocks in such areas as flexible electronics and conductive and high-strength materials, and can serve as templates for ordering plasmonic structures," he said.

By "giant," the researchers referred to irregular flakes of graphene oxide up to 10,000 times as wide as they are high. (That's still impossibly small: on average, roughly 12 microns wide and less than a nanometer high.) Previous studies showed smaller bits of pristine graphene suspended in acid would form a liquid crystal and that graphene oxide would do likewise in other solutions, including water.

This time the team discovered that if the flakes are big enough and concentrated enough, the solution becomes semisolid. When they constrained the gel to a thin pipette and evaporated some of the water, the graphene oxide flakes got closer to each other and stacked up spontaneously, although imperfectly.

"The exciting part for me is the spontaneous ordering of graphene oxide into a liquid crystal, which nobody had observed before," said Behabtu, a member of Pasquali's lab. "It's still a liquid, but it's ordered. That's useful to make fibers, but it could also induce order on other particles like nanorods."

He said it would be a simple matter to heat the concentrated gel and extrude it into something like carbon fiber, with enhanced properties provided by "mix-ins."

Testing the possibilities, the researchers mixed gold microtriangles and glass microrods into the solution, and found both were effectively forced to line up with the pancaking flakes. Their inclusion also helped the team get visual confirmation of the flakes' orientation.

The process offers the possibility of the large-scale ordering and alignment of such plasmonic particles as gold, silver and palladium nanorods, important components in optoelectronic devices and metamaterials, they reported.

Behabtu added that heating the gel "crosslinks the flakes, and that's good for mechanical strength. You can even heat graphene oxide enough to reduce it, stripping out the oxygen and turning it back into graphite."

Co-authors of the paper are Angel Martinez and Julian Evans, graduate students of Smalyukh at the University of Colorado at Boulder.

The Institute for Complex Adaptive Matter, the Colorado Renewable and Sustainable Energy Initiative, the National Science Foundation, the Air Force Research Lab, the Air Force Office of Scientific Research, the Welch Foundation, the U.S. Army Corps of Engineers Environmental Quality and Installation Program and M-I Swaco supported the research.

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Budhadipta Dan, Natnael Behabtu, Angel Martinez, Julian S. Evans, Dmitry V. Kosynkin, James M. Tour, Matteo Pasquali, Ivan I. Smalyukh. Liquid crystals of aqueous, giant graphene oxide flakes. Soft Matter, 2011; DOI: 10.1039/C1SM06418E

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Carbon nanotube muscles generate giant twist for novel motors

ScienceDaily (Oct. 14, 2011) — New artificial muscles that twist like the trunk of an elephant, but provide a thousand times higher rotation per length, have been developed by a team of researchers from The University of Texas at Dallas, The University of Wollongong in Australia, The University of British Columbia in Canada, and Hanyang University in Korea.

The research appears in the journal Science.

These muscles, based on carbon nanotubes yarns, accelerate a 2000 times heavier paddle up to 590 revolutions per minute in 1.2 seconds, and then reverse this rotation when the applied voltage is changed. The demonstrated rotation of 250 per millimeter of muscle length is over a thousand times that of previous artificial muscles, which are based on ferroelectrics, shape memory alloys, or conducting organic polymers. The output power per yarn weight is comparable to that for large electric motors, and the weight-normalized performance of these conventional electric motors severely degrades when they are downsized to millimeter scale.

These muscles exploit strong, tough, highly flexible yarns of carbon nanotubes, which consist of nanoscale cylinders of carbon that are ten thousand times smaller in diameter than a human hair. Important for success, these nanotubes are spun into helical yarns, which means that they have left and right handed versions (like our hands), depending upon the direction of rotation during twisting the nanotubes to make yarn. Rotation is torsional, meaning that twist occurs in one direction until a limiting rotation results, and then rotation can be reversed by changing the applied voltage. Left and right hand yarns rotate in opposite directions when electrically charged, but in both cases the effect of charging is to partially untwist the yarn.

Unlike conventional motors, whose complexity makes them difficult to miniaturize, the torsional carbon nanotube muscles are simple to inexpensively construct in either very long or millimeter lengths. The nanotube torsional motors consist of a yarn electrode and a counter-electrode, which are immersed in an ionically conducting liquid. A low voltage battery can serve as the power source, which enables electrochemical charge and discharge of the yarn to provide torsional rotation in opposite directions. In the simplest case, the researchers attach a paddle to the nanotube yarn, which enables torsional rotation to do useful work -- like mixing liquids on "micro-fluidic chips" used for chemical analysis and sensing.

The mechanism of torsional rotation is remarkable. Charging the nanotube yarns is like charging a supercapacitor -- ions migrate into the yarns to electrostatically balance the electronic charge electrically injected onto the nanotubes. Although the yarns are porous, this influx of ions causes the yarn to increase volume, shrink in length by up to a percent, and torsionally rotate. This surprising shrinkage in yarn length as its volume increases is explained by the yarn's helical structure, which is similar in structure to finger cuff toys that trap a child's fingers when elongated, but frees them when shortened.

Nature has used torsional rotation based on helically wound muscles for hundreds of millions of years, and exploits this action for such tasks as twisting the trunks of elephants and octopus limbs. In these natural appendages, helically wound muscle fibers cause rotation by contracting against an essentially incompressible, bone-less core. On the other hand, the helically wound carbon nanotubes in the nanotube yarns are undergoing little change in length, but are instead causing the volume of liquid electrolyte within the porous yarn to increase during electrochemical charging, so that torsional rotation occurs.

The combination of mechanical simplicity, giant torsional rotations, high rotation rates, and micron-size yarn diameters are attractive for applications, such as microfluidic pumps, valve drives, and mixers. In a fluidic mixer demonstrated by the researchers, a 15 micron diameter yarn rotated a 200 times larger radius and 80 times heavier paddle in flowing liquids at up to one rotation per second.

"The discovery, characterization, and understanding of these high performance torsional motors shows the power of international collaborations," said Ray H. Baughman, a corresponding author of the author of the Science article and Robert A. Welch Professor of Chemistry and director of The University of Texas at Dallas Alan G. MacDiarmid NanoTech Institute. "Researchers from four universities in three different continents that were born in eight different countries made critically important contributions."

Other co-authors of this article are Javad Foroughi (first author and research fellow), Geoffrey M. Spinks (a corresponding author and professor), and Gordon G. Wallace (professor) of the University of Wollongong in Australia; Jiyoung Oh (postdoctoral fellow), Mikhail E. Kozlov (research professor), and Shaoli Fang (research professor) at The University of Texas at Dallas; Tissaphern Mirfakhrai (postdoctoral fellow) and John D. W. Madden (professor) at The University of British Columbia; and Min Kyoon Shin (postdoctoral fellow) and Seon Jeong Kim (professor) at Hanyang University.

Funding for this research was provided by grants from the Air Force Office of Scientific Research, the Air Force AOARD program, the Office of Naval Research MURI program, and the Robert A. Welch Foundation in the United States; the Creative Research Initiative Center for Bio-Artificial Muscle in Korea; the Natural Sciences and Engineering Research Council of Canada; and the Australian Research Council.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Texas at Dallas, via EurekAlert!, a service of AAAS.

Journal Reference:

Javad Foroughi, Geoffrey M. Spinks, Gordon G. Wallace, Jiyoung Oh, Mikhail E. Kozlov, Shaoli Fang, Tissaphern Mirfakhrai, John D. W. Madden, Min Kyoon Shin, Seon Jeong Kim, Ray H. Baughman. Torsional Carbon Nanotube Artificial Muscles. Science, 2011; DOI: 10.1126/science.1211220

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Giant star expels multiple dust shells, astronomers find

ScienceDaily (Sep. 27, 2011) — An international team led by KU Leuven astronomer Leen Decin discovered not less than a dozen cold dust arcs around the giant star CW Leo. The team used the sensitive PACS instrument on board the Herschel Space Observatory to detect for the first time arcs of dust far away from the star. CW Leo has expelled these shells of dust in different epochs in its life. The faintest shell we can see now was, according to the team, expelled about 16,000 years ago. In the mean time it has drifted away from the star over more than 7,000 billion kilometers.

Episodes

"Until recently, the environment of giant stars seemed homogeneous, but more and more observations indicate that this is not true," says Leen Decin. "These new Herschel images confirm that in a stunning way. We have detected a dozen arcs, puffed out by the star in the course of its life. The faintest shell we found is already at a distance of 7,000 billion kilometers from the star."

The different shells were ejected by the star with intervals of 500 to 1,700 years. The astronomers in the team believe such shells, even fainter, are also present further out, up to the violent bow shock where the expelled material of the star collides with the interstellar medium. The oldest shells have probably disappeared in the bow shock already.

Our own Sun too will turn into a red giant star, about five billion years from now, when it will inflate and condensate dust in the outer, cooling layers of its atmosphere. The episodes in CW Leo's history help astronomers understand the future of our own Sun.

Cold

Since the different shells have been travelling far away from the star by now, they are also very cold, about -248°C. The PACS instrument onboard the Herschel Space Telescope was especially designed to make images of the far-infrared light emitted by dust that cold. Thanks to the Belgian participation in the building of the PACS instrument, the team got priority access to the space telescope. Christoffel Waelkens, Co-principal investigator of the PACS instrument consortium is proud of yet another discovery by Herschel: "We had a lot of ideas for science with Herschel, but we also hoped that Herschel would surprise us with unexpected results. It has been a continuous delight since the first observations: at every opportunity nature proves to have more imagination than we have, but still presents us the phenomena so that we can understand them."

Digging in the data

Making the rings visible in the Herschel images was not trivial. Pierre Royer, instrument expert in the PACS team of the Institute of Astronomy at KU Leuven, clarifies: "The work of constantly refining the instrumental calibration and improving the data-analysis techniques really becomes rewarding when it comes to push the instrument to its limits, allowing for cutting-edge science." Also after the Herschel Launch in 2009 the PACS instrument team, including 7 scientists and engineers at KU Leuven, continued to refine the initial calibration and data analysis software.

Publication

The team published the results in the October 2011 issue of the journal Astronomy & Astrophysics.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Katholieke Universiteit Leuven.

Journal Reference:

L. Decin, P. Royer, N. L. J. Cox, B. Vandenbussche, R. Ottensamer, J. A. D. L. Blommaert, M. A. T. Groenewegen, M. J. Barlow, T. Lim, F. Kerschbaum, T. Posch, C. Waelkens. Discovery of multiple dust shells beyond 1?arcmin in the circumstellar envelope of IRC +10216 usingHerschel/PACS. Astronomy & Astrophysics, 2011; 534: A1 DOI: 10.1051/0004-6361/201117360

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Green ring fit for a superhero: Spitzer Space Telescope spies powerful light of giant 'O' stars

ScienceDaily (June 19, 2011) — This glowing emerald nebula seen by NASA's Spitzer Space Telescope is reminiscent of the glowing ring wielded by the superhero Green Lantern. In the comic books, the diminutive Guardians of the Planet "Oa" forged his power ring, but astronomers believe rings like this are actually sculpted by the powerful light of giant "O" stars. O stars are the most massive type of star known to exist.

Named RCW 120 by astronomers, this region of hot gas and glowing dust can be found in the murky clouds encircled by the tail of the constellation Scorpius. The green ring of dust is actually glowing in infrared colors that our eyes cannot see, but show up brightly when viewed by Spitzer's infrared detectors. At the center of this ring are a couple of giant stars whose intense ultraviolet light carved out the bubble, though they blend in with the other stars when viewed in infrared.

Rings like this are so common in Spitzer's observations that astronomers have even enlisted the help of the public to help find and catalog them all. Anyone interested in joining the search as a citizen scientist can visit "The Milky Way Project," part of the "Zooniverse" of public astronomy projects, at http://www.milkywayproject.org/ .

The flat plane of our galaxy is located toward the bottom of the picture, and the ring is slightly above the plane. The green haze seen at the bottom of the image is the diffuse glow of dust from the galactic plane.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. For more information about Spitzer, visit http://spitzer.caltech.edu/ and http://www.nasa.gov/spitzer

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA's Jet Propulsion Laboratory.

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Green ring fit for a superhero: Spitzer Space Telescope spies powerful light of giant 'O' stars

ScienceDaily (June 19, 2011) — This glowing emerald nebula seen by NASA's Spitzer Space Telescope is reminiscent of the glowing ring wielded by the superhero Green Lantern. In the comic books, the diminutive Guardians of the Planet "Oa" forged his power ring, but astronomers believe rings like this are actually sculpted by the powerful light of giant "O" stars. O stars are the most massive type of star known to exist.

Named RCW 120 by astronomers, this region of hot gas and glowing dust can be found in the murky clouds encircled by the tail of the constellation Scorpius. The green ring of dust is actually glowing in infrared colors that our eyes cannot see, but show up brightly when viewed by Spitzer's infrared detectors. At the center of this ring are a couple of giant stars whose intense ultraviolet light carved out the bubble, though they blend in with the other stars when viewed in infrared.

Rings like this are so common in Spitzer's observations that astronomers have even enlisted the help of the public to help find and catalog them all. Anyone interested in joining the search as a citizen scientist can visit "The Milky Way Project," part of the "Zooniverse" of public astronomy projects, at http://www.milkywayproject.org/ .

The flat plane of our galaxy is located toward the bottom of the picture, and the ring is slightly above the plane. The green haze seen at the bottom of the image is the diffuse glow of dust from the galactic plane.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. For more information about Spitzer, visit http://spitzer.caltech.edu/ and http://www.nasa.gov/spitzer

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA's Jet Propulsion Laboratory.

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Astrophysicists use X-ray fingerprints to study eating habits of giant black holes

ScienceDaily (June 7, 2011) — By studying the X-rays emitted when superheated gases plunge into distant and massive black holes, astrophysicists at the Georgia Institute of Technology have provided an important test of a long-standing theory that describes the extreme physics occurring when matter spirals into these massive objects.

Matter falling into black holes emits tremendous amounts of energy which can escape as visible light, ultraviolet light and X-rays. This energy can also drive outflows of gas and dust far from the black hole, affecting the growth and evolution of galaxies containing the black holes. Understanding the complex processes that occur in these active galactic nuclei is vital to theories describing the formation of galaxies such as the Milky Way, and is therefore the subject of intense research.

Though light cannot escape from black holes themselves, black holes with accretion disks -- which are swirling clouds of matter about to enter the black hole -- are among the most luminous objects in galaxies. By studying how the radiation and accretion disk interact, astrophysicists can learn much about the extreme gravitational fields, magnetic forces and radiation processes close to these black holes.

"We reviewed data collected from space telescopes over the past few years and found that the more rapidly a black hole was gobbling up material, the more highly ionized the accretion disk was," said David Ballantyne, an assistant professor in Georgia Tech's School of Physics. "The simple theory of accretion disks predicts this, but the relationship we saw between the ionization and rate of accretion was different from what the theory predicted."

The large difference between the observed and theoretical relationships -- a linear dependence on the rate of accretion as opposed to a cubic dependence -- is not surprising for a phenomenon that can't exactly be tested under controlled laboratory conditions. In a paper published online June 3 in The Astrophysical Journal, Ballantyne describes the research and speculates about possible reasons for the difference between observations and theory. The research, which will appear in the Journal's June 20 issue, was supported in part by the National Science Foundation (NSF).

"As in many areas of science, especially astronomy, we end up needing more data -- many more high-quality observations to better define this relationship," he added.

Astrophysicists don't have a detailed understanding of how the accretion process works, why black holes grow at different rates -- or what makes them stop growing. These questions are important because the growth of active galactic nuclei -- the black holes and their surrounding accretion disks -- has broader effects on the galaxies of which they are part.

"The rapid accretion phase releases a lot of energy, not only in radiation, but also in outflows that drive gas out of a galaxy, which can shut off star formation and hold back the growth of the galaxy," said Ballantyne, a scientist in Georgia Tech's Center for Relativistic Astrophysics. "We could potentially learn something fundamental about the flow of energy through the accretion disk very close to the black hole. We could learn about the viscosity of this matter and how efficiently radiation transport takes place. These are very important questions in astrophysics."

X-rays are believed to originate from innermost portion of active galactic nuclei. As they pass through matter on its way into the black hole, the X-rays are altered by the materials in ways that astrophysicists can measure. In their study, Ballantyne and his collaborators were interested in studying the ionization state of the matter -- which is related to the illumination -- and were able to do so by analyzing the "fingerprint" the ionization left on the X-rays.

"From laboratory work, we understand the physics of how gas interacts with X-ray radiation because that's basically an atomic physics problem," he explained. "We can model what these fingerprints might look like on the X-rays, and compare that to the actual data to help us understand what's going on."

Because of their high energy and short wavelength, X-rays pass through many materials, such as human bodies, with little attenuation. This makes them ideal for examining processes in active galactic nuclei. Longer wavelengths, such as ultraviolet and visible light, are absorbed by intergalactic dust, or are difficult to distinguish from light originating in stars. However, X-rays do get absorbed by dense objects, such as bones -- and crucially for this study -- accretion disks.

Ballantyne and his collaborators Jon McDuffie and John Rusin studied ten X-ray observations reported by other scientists from eight different active galactic nuclei. The observations were made using such space telescopes as Chandra and XMM.

To be useful, they used only measurements of X-ray emissions from the innermost and hottest portion of the accretion disk, and only where the mass of the black holes -- which range from a million to a billion times the size of our sun -- had high quality estimates.

In pursuing the study, Ballantyne hopes to maintain the involvement of Rusin, a student from South Cobb High School in Marietta, near Atlanta. Rusin became involved when he contacted Georgia Tech to inquire about astrophysics projects.

"He helped us with data acquisition and was a really big help," said Ballantyne. "I treated him just like an undergraduate student. I'm pleased to know that he has decided to attend Georgia Tech."

The next step in the research will be to gather additional information from other studies of active galactic nuclei to see if the linear relationship Ballantyne's group measured holds up. The work may also lead to other techniques for learning about black holes and the accretion process.

"Black holes themselves are very simple, but what goes on around them can be very complex," Ballantyne said. "There is still a lot to be learned about how black holes get fueled, and how some accrete slowly while others grow rapidly. The astrophysics of black holes is actually very important in determining what our universe looks like."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Georgia Institute of Technology Research News. The original article was written by John Toon.

Journal Reference:

D. R. Ballantyne, J. R. McDuffie, J. S. Rusin. A Correlation between the Ionization State of the Inner Accretion Disk and the Eddington Ratio of Active Galactic Nuclei. The Astrophysical Journal, 2011; 734 (2): 112 DOI: 10.1088/0004-637X/734/2/112

Note: If no author is given, the source is cited instead.

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Giant ants once roamed Wyoming

SERIOUS ANTA fossil ant queen found in Wyoming is the size of a rufous hummingbird’s body and is the first giant ant species documented by more than a wing in North America.© Bruce Archibald

It’s not a bird or a plane, but it is an ant the size of a hummingbird.

A winged ant queen fossilized in 49.5-million-year-old Wyoming rock ranks as the first body of a giant ant from the Western Hemisphere, says paleoentomologist Bruce Archibald of Simon Fraser University in Burnaby, Canada.

The new species, Titanomyrma lubei, is related to giant ants previously found in German fossils. These long-distance relatives bolster the notion that the climate of the time had hot blips that allowed warmth-loving giant insects to spread from continent to continent, Archibald and a U.S.-Canada team propose online May 4 in the Proceedings of the Royal Society B.

An ancient ant wing from Tennessee had hinted that big ants lived in North America during this time, says Torsten Wappler of the University of Bonn in Germany. “But complete preserved specimens were not known until Bruce came up with this beautiful preserved fossil.”

The new fossil caught Archibald’s eye as he and coauthor Kirk Johnson poked around storage drawers at the Denver Museum of Nature & Science, where Johnson works. The spookiest thing about the Wyoming ant may be that even at 5.1 centimeters long, she is not the largest ant ever found. A German specimen is slightly longer, as are queens of a living African driver ant, Dorylus wilverthi.

Although ants overall trend toward greater size in cooler places, Archibald notes that the eight largest living species dwell mostly in the tropics. The team looked at climate reconstructions for the fossil species and found hot spots where the ancient giants lived as well.

For a tropical lineage to have sprawled between continents meant taking ancient land bridges through Greenland or Iceland. During much of the ants’ time those northern routes were merely temperate. But brief hot spells were possible, Archibald and his colleagues say. Climate scientists have already suggested there were several around 50 million years ago; one, for example, lasted about 170,000 years.

That idea of tropical moments of opportunity fits the interpretation of other fossils from the far north, says paleoclimatologist Appy Sluijs of Utrecht University in the Netherlands. Findings in northern regions of preserved hippo predecessors, tropical plankton and pollen from tropical palms support the idea. Now, he says, “The major challenge is to explain how a region that does not receive sunlight for 6 months keeps from freezing its giant ants and other creatures that don’t tolerate frost.”

Community ecologist Michael Kaspari of the University of Oklahoma in Norman has studied the cooler-bigger connection and says that so far he’s “agnostic” about whether supersized ant species have tropical tastes. In any case, he says, the new species ranks as “a magnificent ant.”

Found in: Earth, Environment and Life

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