Pluto’s Atmosphere Boasts Methane, Warmer Temps

 

Artist’s impression of how the surface of Pluto might look, if patches of pure methane rest on the surface. At the distance of Pluto, the Sun appears about 1,000 times fainter than on Earth. Credit: ESO

 

Pluto is certainly frigid, but new research has revealed its atmosphere is a bit warmer.

Astronomers using the European Southern Observatory’s Very Large Telescope have found unexpectedly large amounts of methane in Pluto’s atmosphere, which evidently helps it stay about 40 degrees warmer than the dwarf planet’s surface. The atmosphere warms to -180 degrees Celsius (-356 degrees Fahrenheit), compared to a surface that’s usually -220 degrees Celsius (-428 degrees Fahrenheit).

“With lots of methane in the atmosphere, it becomes clear why Pluto’s atmosphere is so warm,” said Emmanuel Lellouch of the Observatoire de Paris in France. Lellouch is lead author of the paper reporting the results, which is in press at the journal Astronomy and Astrophysics.

Pluto, which is about a fifth the size of Earth, is composed primarily of rock and ice and orbits about 40 times further from the Sun than the Earth.

It has been known since the 1980s that Pluto also has a thin, tenuous atmosphere. Abundant nitrogen, along with traces of methane and probably carbon monoxide, are held to the surface by an atmospheric pressure only about one hundred thousandth of that on Earth, or about 0.015 millibars. As Pluto moves away from the Sun, during its 248 year-long orbit, its atmosphere gradually freezes and falls to the ground. In periods when it is closer to the Sun — as it is now — the temperature of Pluto’s solid surface increases, causing the ice to sublimate into gas.

Until recently, only the upper parts of the atmosphere of Pluto could be studied. By observing stellar occultations, a phenomenon that occurs when a Solar System body blocks the light from a background star, astronomers were able to demonstrate that Pluto’s upper atmosphere was some 50 degrees warmer than the surface. Those observations couldn’t shed any light on the atmospheric temperature and pressure near Pluto’s surface. But unique, new observations made with the CRyogenic InfraRed Echelle Spectrograph (CRIRES), attached to ESO’s Very Large Telescope, have now revealed that the atmosphere as a whole, not just the upper atmosphere, has a mean temperature much less frigid than the surface.

Usually, air near the surface of the Earth is warmer than the air above it, largely because the atmosphere is heated from below as solar radiation warms the Earth’s surface, which, in turn, warms the layer of the atmosphere directly above it. Under certain conditions, this situation is inverted so that the air is colder near the surface of the Earth. Meteorologists call this an inversion layer, and it can cause smog build-up.

Most, if not all, of Pluto’s atmosphere is thus undergoing a temperature inversion: the temperature is higher, the higher in the atmosphere you look. The change is about 3 to 15 degrees per kilometer (.62 miles). On Earth, under normal circumstances, the temperature decreases through the atmosphere by about 6 degrees per kilometer.

The reason why Pluto’s surface is so cold is linked to the existence of Pluto’s atmosphere, and is due to the sublimation of the surface ice; much like sweat cools the body as it evaporates from the surface of the skin, this sublimation has a cooling effect on the surface of Pluto.

The CRIRES observations also indicate that methane is the second most common gas in Pluto’s atmosphere, representing half a percent of the molecules. “We were able to show that these quantities of methane play a crucial role in the heating processes in the atmosphere and can explain the elevated atmospheric temperature,” said Lellouch.

Two different models can explain the properties of Pluto’s atmosphere. In the first, the astronomers assume that Pluto’s surface is covered with a thin layer of methane, which will inhibit the sublimation of the nitrogen frost. The second scenario invokes the existence of pure methane patches on the surface.

“Discriminating between the two will require further study of Pluto as it moves away from the Sun,” says Lellouch. “And of course, NASA’s New Horizons space probe will also provide us with more clues when it reaches the dwarf planet in 2015.”

LEAD IMAGE CAPTION: Artist’s impression of how the surface of Pluto might look, if patches of pure methane rest on the surface. At the distance of Pluto, the Sun appears about 1,000 times fainter than on Earth. Credit: ESO

Source: ESO

Titan Dunes Turn Climate Models Upside Down

Scientists have mapped vast dune fields on Titan that may align with the wind on Saturn’s biggest moon — flowing opposite the way climate models had predicted.

The maps, as above, represent four years of radar data collected by the Cassini spacecraft. They reveal rippled dunes that are generally oriented east-west, which means Titan’s winds probably blow toward the east instead of the west. If so, Titan’s surface winds blow opposite the direction suggested by previous global circulation models. On the example above, the arrows indicate the general wind direction. The dark areas without arrows might have dunes but have not yet been imaged. 

“At Titan there are very few clouds, so determining which way the wind blows is not an easy thing, but by tracking the direction in which Titan’s sand dunes form, we get some insight into the global wind pattern,” says Ralph Lorenz, Cassini radar scientist at Johns Hopkins University in Maryland. “Think of the dunes sort of like a weather vane, pointing us to the direction the winds are blowing.”

Titan’s dunes are believed to be made up of hydrocarbon sand grains likely derived from organic chemicals in Titan’s smoggy skies. The dunes wrap around high terrain, which provides some idea of their height. They accumulate near the equator, and may pile up there because drier conditions allow for easy transport of the particles by the wind. Titan’s higher latitudes contain lakes and may be “wetter” with more liquid hydrocarbons, not ideal conditions for creating dunes.

“Titan’s dunes are young, dynamic features that interact with topographic obstacles and give us clues about the wind regimes,” said Jani Radebaugh, from Brigham Young University in Utah. “Winds come at these dunes from at least a couple of different directions, but then combine to create the overall dune orientation.”

Researchers say the wind pattern is important for planning future Titan explorations that might involve balloon-borne experiments. Some 16,000 dune segments were mapped out from about 20 radar images, digitized and combined to produce the new map, which is available at http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. A paper based on the new findings appeared in the Feb. 11 issue of Geophysical Research Letters.

Cassini, which launched in 1997 and is now in extended mission operations, continues to blaze its trail around the Saturn system and will visit Titan again on March 27. Seventeen Titan flybys are planned this year.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA’s Jet propulsion Laboratory (JPL) in Pasadena, California manages the Cassini-Huygens mission. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

LEAD IMAGE CREDIT: NASA/JPL/Space Science Institute (Boulder, Colorado)

Source: NASA

Jupiter, Saturn Plowed Through Asteroids, Study Says

Asteroids

 

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When Mars and Jupiter migrated to their present orbits around 4 billion years ago, they left scars in the asteroids belt that are still visible today.

The evidence is unveiled in a new paper in this week’s issue of the journal Nature, by planetary scientists David Minton and Renu Malhotra from the University of Arizona in Tucson.  

The asteroid belt has long been known to harbor gaps, called Kirkwood gaps, in distinct locations. Some of these gaps correspond to unstable zones, where the modern-day gravitational influence of Jupiter and Saturn eject asteroids. But for the first time, Minton and Malhotra have noticed that some clearings don’t fit the bill.

“What we found was that many regions are depleted in asteroids relative to other regions, not just in the previously known Kirkwood gaps that are explained by the current planetary orbits,” Minton wrote in an email. In an editorial accompanying the paper, author Kevin Walsh added, “Qualitatively, it looks as if a snow plough were driven through the main asteroid belt, kicking out asteroids along the way and slowing to a stop at the inner edge of the belt.” 

Walsh hails from the Observatoire de la Côte d’Azur in France. In his News and Views piece, he explains that the known Kirkwood gaps, discovered by Daniel Kirkwood in 1867, “correspond to the location of orbital resonances with Jupiter — that is, of orbits whose periods are integer ratios of Jupiter’s orbital period.” For example, if an asteroid orbited the Sun three times for every time Jupiter did, it would be in a 3:1 orbital resonance with the planet, he wrote. Objects in resonance with a giant planet have inherently unstable orbits, and are likely to be ejected from the solar system. When planets migrated, astronomers believe objects in resonance with them also shifted, affecting different parts of the asteroid belt at different times. 

“Thus, if nothing has completely reshaped the asteroid belt since the planets settled into their current orbits, signatures of past planetary orbital migration may still remain,” Walsh wrote. And that’s exactly what Minton and Malhotra sought.

The asteroid belt easily gave up its secrets, showing the lingering evidence of planetary billiards on the inner edge of the asteroid belt and at the outer edge of each Kirkwood gap. The new finding, based on computer models, lends additional support to the theory that the giant planets — Jupiter, Saturn, Uranus and Neptune — formed twice as close to the sun as they are now and in a tighter configuration, and moved slowly outward. 

“The orbit of Pluto and other Kuiper belt objects that are trapped in [orbits that resonate] with Neptune can be explained by the outward migration of Neptune,” Minton and Malhotra write in the new study. “The exchange of angular momentum between planetesimals and the four giant planets caused the orbital migration of the giant planets until the outer planetesimal disk was depleted.”  Planetesimals are rocky and icy objects left over from planet formation.

“As Jupiter and Saturn migrated,” the authors continue, they wreaked havoc on the young asteroid belt, “exciting asteroids into terrestrial planet-crossing orbits, thereby greatly depleting the asteroid belt population and perhaps also causing a late heavy bombardment in the inner Solar System.”

The late heavy bombardment is proposed to have occurred about 3.9 billion years ago, or 600 million years after the birth of the Solar System, and it’s believed to account for many of the Moon’s oldest craters. Walsh said a reasonable next step, to corroborate the theory about the newly described clearings in the asteroid belt, is to link them chronologically with the bombardment.

LEAD PHOTO CAPTION: Artist’s depiction of the asteroid belt between Mars and Jupiter. Credit: David Minton and Renu Malhotra

Source: Nature

Penetrating New View Into The Helix Nebula

 

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ESO’s La Silla Observatory has snapped a new image of the famous Helix planetary nebula, revealing a rich — and rarely photographed — background of distant galaxies.

The Helix Nebula, NGC 7293, about 700 light-years away in the constellation of Aquarius, is a Sun-like star in its final explosion before retirement as a white dwarf.

Shells of gas are blown off from the surface of such stars, often in intricate and beautiful patterns, and shine under the harsh ultraviolet radiation from the faint, hot central star. The main ring of the Helix Nebula is about two light-years across, or half the distance between the Sun and its nearest stellar neighbour.

Despite being photographically spectacular, the Helix is hard to see visually as its light is thinly spread over a large area of sky. The history of its discovery is rather obscure. It first appears in a list of new objects compiled by the German astronomer Karl Ludwig Harding in 1824. The name Helix comes from the rough corkscrew shape seen in the earlier photographs.

Although the Helix looks very much like a doughnut, studies have shown that it possibly consists of at least two separate discs with outer rings and filaments. The brighter inner disc seems to be expanding at about 100,000 km/h (about 62,000 miles/h) and to have taken about 12,000 years to form.

Because the Helix is relatively close — it covers an area of the sky about a quarter of the full Moon — it can be studied in much greater detail than most other planetary nebulae and has been found to have an unexpected and complex structure. All around the inside of the ring are small blobs, known as “cometary knots,” with faint tails extending away from the central star. Although they look tiny, each knot is about as large as our Solar System. These knots have been extensively studied, both with the ESO Very Large Telescope and with the NASA/ESA Hubble Space Telescope, but remain only partially understood. A careful look at the central part of this object reveals not only the knots, but also many remote galaxies seen right through the thinly spread glowing gas. Some of these seem to be gathered in separate galaxy groups scattered over various parts of the image.

For a sweet treat, throw a little of this into your coffee: Helix Nebula pan and zoom (video)

LEAD IMAGE CAPTION: The blue-green glow in the center of the Helix comes from oxygen atoms shining under effects of the intense ultraviolet radiation of the 120,000 degree Celsius (about 216,000 degrees F) central star and the hot gas. Further out from the star and beyond the ring of knots, the red color from hydrogen and nitrogen is more prominent. Credit: Max-Planck Society/ESO telescope at the La Silla observatory in Chile

Source: ESO

Arizona Scientist: We Could All Be Martians

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As long as we’re still pondering human origins, we may as well entertain the idea that our ancestor microbes came from Mars.

And Jay Melosh, a planetary scientist from the University of Arizona in Tucson, is ready with a geologically plausible explanation.

Meteorites.

“Biological exchange between the planets of our solar system seem not only possible, but inevitable,” because of meteorite exchanges between the planets, Melosh said. “Life could have originated on the planet Mars and then traveled to Earth.”

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Jay Melosh. Credit: Maria Schuchardt, University of Arizona Lunar and Planetary Lab

Melosh is a long-time researcher who says he’s studied “geological violence in all its forms.” He helped forge the giant impact theory of the moon’s formation, and helped advance the theory that an impact led to the extinction of the dinosaurs 65 million years ago.

He points out that Martian meteorites have been routinely pummeling Earth for billions of years, which would have opened the door for past Mars microbes to hitch a ride. Less regularly, Earth has undergone impacts that sent terrestrial materials flying, and some of those could have carried microbes toward the Red Planet.

“The mechanism by which large impacts on Mars can launch boulder-sized surface rocks into space is now clear,” he said. He explained that a shock wave spreads away from an impact site faster than the speed of sound, interacting with the planetary surface in a way that allows material to be cast off – at relatively low pressure, but high speed.

“Lightly damaged material at very high speeds,” he said, “is the kind of environment where microorganisms can survive.”

Scientists have recent evidence of Earth microbes surviving a few years in space. When the Apollo 12 astronauts landed on the moon, they retrieved a camera from Surveyor 3, an unmanned lander that had touched down nearly three years prior. Earthly microbes – including those associated with the common cold — were still living inside the camera box.

“The records were good enough to show one of the technicians had a cold when he was working on it,” he said.

Scientists also have evidence that microbes can survive for thousands or even hundreds of thousands of years when frozen on Earth, but surviving that long in space would be an entirely different matter, with the bombardment of UV light and cosmic rays. Then again, the microbe Dienococcus radiodurans is known to survive in the cores of nuclear reactors.

Melosh acknowledges that scientists lack proof that such an exchange has actually occurred between Mars and Earth — but science is getting ever closer to being able to track it down. 

LEAD PHOTO CAPTION: Artist’s conception of an fragment as it blasts off from Mars. Boulder-sized planetary fragments could be a mechanism that carried life between Mars and Earth, UA planetary scientist Jay Melosh says. (Painting by Don Davis. Copyright SETI Institute, 1994)

Source: University of Arizona and an interview with Jay Melosh

NASA Delays Discovery Launch Fourth Time

 

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NASA announced yet another delay for the launch of the Discovery STS-119 mission to the International Space Station Friday, marking the fourth time the mission has been postponed.

An all-day review of the craft’s readiness for launch left managers still under-confident about the operations of three hydrogen control valves that channel gaseous hydrogen from the main engines to the external fuel tank. Engineering teams have been working to identify what caused damage to a flow control valve on shuttle Endeavour during its November 2008 flight. NASA managers decided Friday more data and possible testing are required before launch can proceed.

“We need to complete more work to have a better understanding before flying,” said Bill Gerstenmaier, associate administrator for Space Operations at NASA Headquarters in Washington. Gerstenmaier chaired Friday’s Flight Readiness Review. 

“We were not driven by schedule pressure and did the right thing. When we fly, we want to do so with full confidence.”

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The STS-119 crew members gather in front of the hatch into space shuttle Discovery to place the mission plaque. Standing from left are Mission Specialists Joseph Acaba, Koichi Wakata, Steve Swanson, John Phillips and Richard Arnold and Pilot Tony Antonelli. Kneeling in front is Commander Lee Archambault. Photo credit: NASA/Kim Shiflett January 20, 2009

 

Besides understanding what happened with Endeavor’s valves last fall, teams also have tried to determine the consequences if a valve piece were to break off and strike part of the shuttle and external fuel tank.

Meanwhile, the Discovery launch date has shifted from Feb. 12, to Feb. 19, to Feb. 22, Feb. 27 and now — as of last night’s briefing — is postponed until further notice. The Space Shuttle Program has been asked to develop a plan for further inspections. The plan will be reviewed during a meeting on Wednesday, Feb. 25 and a new target launch date may be considered then.

The STS-119 mission is supposed to enhance the solar gathering power of the International Space Station so it might support a larger crew. When it does fly,  STS-119 will tote two solar array wings, each of which has two 115-foot-long arrays, for a total wing span of 240 feet, including the equipment that connects the two halves and allows them to twist as they track the sun. Altogether, the four sets of arrays can generate 84 to 120 kilowatts of electricity – enough to provide power for more than 40 average homes.

The mission astronauts arrived at the Kennedy Space Center Jan. 19 and have more or less been in standby mode ever since, shuttling back and forth between Florida and the Johnson Space Center in Houston. On Wednesday of this week, STS-119 mission specialists Richard Arnold and Joseph Acaba were in the Neutral Buoyancy Laboratory at Johnson, brushing up on spacewalk procedures. As of Thursday, the astronauts were in launch-countdown mode which included preflight quarantine.

Sweet Potatoes Flew into Space Aboard Columbia

 

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A team of researchers from the Deep South sent sweet potato plants into space, as part of an experiment aimed at providing food for long-term space missions.

Desmond G. Mortley, from the G.W. Carver Agricultural Experiment Station at Alabama’s Tuskegee University, and his colleagues launched the sweet potato cuttings on a five-day mission aboard the space shuttle Columbia, and compared their success to ground-based cuttings at Kennedy Space Center in Florida.

“The intent of the experiment was to study if stem cuttings would be a successful means of propagating plants in space, just as they are on Earth,” said Raymond Wheeler, a study co-author from NASA’s Biological Science Office at the Kennedy Space Center. “The results showed that the cuttings did indeed produce adventitious roots in microgravity, suggesting that cuttings should work well in space settings.”

The sweet potato experiment was flown on Columbia’s July 1999 mission to the Chandra X-Ray Observatory. The study findings were published in the May 2008 issue of the Journal of American Society for Horticultural Science, although a public press release was issued just this week.

Seeds of several crops have been grown in microgravity, but this was the first test for plants grown from cuttings. Cuttings grow roots faster than seeds do, and sweet potato cuttings regenerate very easily. This made them ideal for the study.

According to the study authors, all of the cuttings produced roots and growth was “quite vigorous in both ground-based and flight samples.” Except for a slight browning of some root tips in the flight samples, all of the stem cuttings appeared normal, they added. The roots on the flight cuttings tended to grow in random directions, sometimes perpendicular to the stems. Also, stem cuttings grown in microgravity had more roots and longer roots than ground-based controls.

The next step, Mortley and his colleagues say, will be to experiment over longer space missions to test root cuttings’ ability to grow plants.

Source: Eurekalert and Journal of American Society for Horticultural Science.

NASA’s Kepler Mission Ready for Launch

 

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NASA’s Kepler spacecraft is ready to be moved to the launch pad today and will blast off within weeks, with a mission to address an age-old question: Are we alone?

Kepler is scheduled to blast into space from Florida’s Cape Canaveral Air Force Station aboard a Delta II rocket on March 5 at 10:48 p.m. eastern time (7:48 p.m. Pacific). It is the first mission with the ability to find planets like Earth — rocky planets that orbit sun-like stars in a warm zone where liquid water could be maintained on the surface. If Earth-sized and slightly larger planets are as common around other stars as some astronomers suspect, Kepler could spy hundreds of them within the next few years.

If so, “life may well be common throughout our universe,” said William Borucki, NASA’s principal investigator for Kepler science, who spoke about the mission Thursday afternoon at a NASA press conference. “If on the other hand we don’t find any, that will be another profound discovery. In fact it will mean there will be no Star Trek.”

 

The Kepler mission will spend three and a half years surveying more than 100,000 sun-like stars in the Cygnus-Lyra region of our Milky Way galaxy.  Its telescope is specially designed to detect the periodic dimming of stars that planets cause as they pass by. Some star systems are oriented in such a way that their planets cross in front of their stars, as seen from our Earthly point of view. As the planets pass by, they cause their stars’ light to slightly dim, or wink.

The telescope can detect even the faintest of these winks, registering changes in brightness of only 20 parts per million. To achieve this resolution, Kepler will use the largest camera ever launched into space, a 95-megapixel array of charged couple devices, known as CCDs.

“If Kepler were to look down at a small town on Earth at night from space, it would be able to detect the dimming of a porch light as somebody passed in front,” James Fanson, Kepler project manager at NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a press release. During the briefing he added that the resolution is “akin to measuring a flea as it creeps across the headlight of an automobile at night. That’s the level of precision we have to achieve.”

Fanson added that Kepler, at a cost of about $500 million, is “the most complex piece of space flight hardware ever built” by the Boulder, Colorado-based Ball Aerospace & Technologies Corp.

The exoplanet research field has already proven exciting, Borucki said. Just over three hundred exoplanets have been detected so far, most of them gas giants like Jupiter and Saturn because those are the easiest to spot with pre-Kepler instruments. Already, the known exoplanets are an eclectic bunch.

“We’re finding planets that [would] float like foam on water,” Borucki said. “We’re finding planets with the density of lead.” And whereas researchers were expecting planet with orderly, circular orbits and sizes that increased with distances from stars, they’re finding a chaotic mix of behaviors — eccentric orbits, and giant, gaseous worlds so close to their parent stars that they complete full orbits within days.

By staring at one large patch of sky for the duration of its lifetime, Kepler will be able to watch planets periodically transit their stars over multiple cycles, allowing astronomers to confirm the presence of planets and use the Hubble and Spitzer space telescopes, along with ground-based telescopes, to characterize their atmospheres and orbits. Earth-size planets in habitable zones would theoretically take about a year to complete one orbit, so Kepler will monitor those stars for at least three years to confirm the planets’ presence.

The first objects likely to be reported will be the Jupiter- and Saturn-sized planets, and gradually — as confirmations roll in and detections get more focused — Neptune and then Earth-sized detections will be more likely to emerge, said exoplanet hunter Debra Fischer of San Francisco State University in California, who is not directly involved with the mission.

“We have a good chance of finding Mars-size planets, and a possibility of finding Mercury-sized planets” with Kepler, she said. “We don’t think we can do better than that.”

The scientists are in no rush to announce new discoveries until they’re “bulletproof,” they said — which could translate into years of suspense for the world’s Trekkies.

“We don’t want to have false discoveries,” Borucki said. “We want to be sure when we say it’s an earth, its an earth.”

Source: NASA teleconference and press release.

Fermi Glimpses Wildest-Ever Gamma-Ray Blast

GRB 080916C’s X-ray afterglow appears orange and yellow in this view that merges images from Swift’s UltraViolet/Optical and X-ray telescopes. Credit: NASA/Swift/Stefan Immler

 
Researchers using the Fermi Gamma-ray Space Telescope are reporting a gamma-ray explosion that blows away anything they’ve seen before. The blast, recorded last fall in the constellation Carina, released the energy of 9,000 supernovae.

The collapse of very massive stars can produce violent explosions, accompanied by strong bursts of gamma-ray light, which are some of the brightest events in the universe. Typical gamma-ray bursts emit photons with energies between 10 kiloelectron volts and about 1 megaelectron volt. Photons with energies above megaelectron volts have been seen in some very rare occasions but the distances to their sources were not known. An international research consortium is reporting in this week’s issue of the journal Science Express that the Fermi Gamma-Ray Space Telescope has detected photons with energies between 8 kiloelectron volts and 13 gigaelectron volts arriving from the gamma-ray burst 080916C.

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Fermi, formerly known as GLAST, pictured pre-launch in the spring of 2008. Photo credit: NASA/Dimitri Gerondidakis

The explosion, designated GRB 080916C, occurred just after midnight GMT on September 16 (7:13 p.m. on the 15th in the eastern US). Two of Fermi’s science instruments — the Large Area Telescope and the Gamma-ray Burst Monitor — simultaneously recorded the event. Together, the two instruments provide a view of the blast’s gamma-ray emission from energies ranging from 3,000 to more than 5 billion times that of visible light.

A team led by Jochen Greiner at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, established that the blast occurred 12.2 billion light-years away using the Gamma-Ray Burst Optical/Near-Infrared Detector (GROND) on the 2.2-meter (7.2-foot) telescope at the European Southern Observatory in La Silla, Chile.

“Already, this was an exciting burst,” says Julie McEnery, a Fermi deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But with the GROND team’s distance, it went from exciting to extraordinary.”

Astronomers believe most gamma-ray explosions occur when exotic massive stars run out of nuclear fuel. As a star’s core collapses into a black hole, jets of material — powered by processes not yet fully understood — blast outward at nearly the speed of light. The jets bore all the way through the collapsing star and continue into space, where they interact with gas previously shed by the star. This generates bright afterglows that fade with time.

The burst is not only spectacular but also enigmatic: a curious time delay separates its highest-energy emissions from its lowest. Such a time lag has been seen clearly in only one earlier burst, and researchers have several explanations for why it may exist. It is possible that the delays could be explained by the structure of this environment, with the low- and high-energy gamma rays “coming from different parts of the jet or created through a different mechanism,” said Large Area Telescope Principal Investigator Peter Michelson, a Stanford University physics professor affiliated with the Department of Energy.

Another, far more speculative theory suggests that perhaps time lags result not from anything in the environment around the black hole, but from the gamma rays’ long journey from the black hole to our telescopes. If the theorized idea of quantum gravity is correct, then at its smallest scale space is not a smooth medium but a tumultuous, boiling froth of “quantum foam.” Lower-energy (and thus lighter) gamma rays would travel faster through this foam than higher-energy (and thus heavier) gamma rays. Over the course of 12.2 billion light years, this very small effect could add up to a significant delay.

The Fermi results provide the strongest test to date of the speed of light’s consistency at these extreme energies. As Fermi observes more gamma-ray bursts, researchers can look for time lags that vary with respect to the bursts. If the quantum gravity effect is present, time lags should vary in relation to the distance. If the environment around the burst origin is the cause, the lag should stay relatively constant no matter how far away the burst occurred.

“This one burst raises all sorts of questions,” Michelson says. “In a few years, we’ll have a fairly good sample of bursts, and may have some answers.”

Source: Eurekalert

New Recipe for Dwarf Galaxies: Start with Leftover Gas

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Apparently, dwarf galaxies can spring out of thin air.

Astronomers using NASA’s Galaxy Evolution Explorer have spotted unexpected new galaxies in the constellation Leo that appear to be forming out of nothing more than pristine gas, probably leftover from the early universe.  The gas lacks both dark matter and metals — previously thought to be building blocks for galaxy formation.

Dwarf galaxies are relatively small collections of stars that often orbit around larger galaxies like our Milky Way. Though never seen before, the researchers say this new type of dwarf galaxy may be common throughout the more distant and early universe, when pristine gas was more pervasive. Their discovery appears in this week’s issue of the journal Nature.

The newly described dwarf galaxies are in the Leo Ring, a huge cloud of hydrogen and helium that traces a ragged path around two massive galaxies in the constellation Leo. The cloud is thought likely to be a primordial object, an ancient remnant of material that has remained relatively unchanged since the very earliest days of the universe. Identified about 25 years ago by radio waves, the ring cannot be seen in visible light.

“This intriguing object has been studied for decades with world-class telescopes operating at radio and optical wavelengths,” said lead study author David Thilker of Johns Hopkins University in Baltimore. He added that no stars were ever seen in the gaseous regions before. 

“But when we looked at the ring with the Galaxy Evolution Explorer, which is remarkably sensitive to ultraviolet light, we saw telltale evidence of recent massive star formation. It was really unexpected. We are witnessing galaxies forming out of a cloud of primordial gas.”

Our local universe contains two large galaxies, the Milky Way and the Andromeda galaxy, each with hundreds of billions of stars, and the Triangulum galaxy, with several tens of billions of stars. It also holds more than 40 much smaller dwarf galaxies, which have only a few billion stars. Invisible dark matter, detected by its gravitational influence, is a major component of both giant and dwarf galaxies with one exception — tidal dwarf galaxies.

Tidal dwarf galaxies condense out of gas recycled from other galaxies and have been separated from most of the dark matter with which they were originally associated. They are produced when galaxies collide and their gravitational masses interact. In the violence of the encounter, streamers of galactic material are pulled out away from the parent galaxies and the halos of dark matter that surround them.

Because they lack dark matter, the new galaxies observed in the Leo Ring resemble tidal dwarf galaxies, but they differ in a fundamental way. The gaseous material making up tidal dwarfs has already been cycled through a galaxy. It has been enriched with metals — elements heavier than helium — produced as stars evolve. “Leo Ring dwarfs are made of much more pristine material without metals,” Thilker said. “This discovery allows us to study the star formation process in gas that has not yet been enriched.”

Large, pristine clouds similar to the Leo Ring may have been more common throughout the early universe, Thilker said, and consequently may have produced many dwarf galaxies yet to be discovered that also lack dark matter.

Source: Caltech

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The forming dwarf galaxies shine in the far ultraviolet spectrum, rendered as blue in the call-out on the right hand side of this image. Near ultraviolet light, also obtained by the Galaxy Evolution Explorer, is displayed in green, and visible light from the blue part of the spectrum here is represented by red. The clumps (in circles) are distinctively blue, indicating they are primarily detected in far ultraviolet light. The faint blue overlay traces the outline of the Leo Ring, a huge cloud of hydrogen and helium that orbits around two massive galaxies in the constellation Leo (left panel). Credit: NASA/JPL-Caltech/DSS