New Class Of Pulsars Solve Mystery Of Previously Unidentified Gamma-ray Sources

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ScienceDaily (July 3, 2009) — A new class of pulsars detected by NASA's Fermi Gamma-ray Space Telescope is solving the mystery of previously unidentified gamma-ray sources and helping scientists understand the mechanisms behind pulsar emissions.

A study to be published by an international team of scientists in the July 2 edition of Science Express describes 16 pulsars discovered by Fermi based on their pulsed emissions of high-energy gamma rays. A pulsar is a rapidly spinning neutron star, the dense core left behind after a supernova explosion. Most of the 1,800 known pulsars were found through their periodic radio emissions.
"These are the first pulsars ever detected by gamma rays alone, and already we've found 16," said coauthor Robert Johnson, professor of physics at the University of California, Santa Cruz. "The existence of a large population of radio-quiet pulsars was suspected prior to this, but until Fermi was launched, only one radio-quiet pulsar was known, and it was first detected in x-rays."
Johnson and other physicists at UCSC's Santa Cruz Institute for Particle Physics (SCIPP) identified the gamma-ray pulsars using computational techniques they developed to comb through data from Fermi's Large Area Telescope (LAT). Marcus Ziegler, a postdoctoral researcher at SCIPP and corresponding author of the paper, said detection of gamma-ray pulsations from a typical source requires weeks or months of data from the LAT.
"From the faintest pulsar we studied, the LAT sees only two gamma-ray photons a day," Ziegler said.
Of the 16 gamma-ray pulsars found by Fermi, 13 are associated with unidentified gamma-ray sources detected previously by the EGRET instrument on the Compton Gamma-ray Observatory. EGRET detected nearly 300 gamma-ray point sources, but was unable to detect pulsations from those sources, most of which have remained unidentified, said Pablo Saz Parkinson, also a SCIPP postdoctoral researcher and corresponding author of the paper.
"It's been a longstanding question what could be powering those unidentified sources, and the new Fermi results tell us that a lot of them are pulsars," Saz Parkinson said. "These findings are also giving us important clues about the mechanism of pulsar emissions."
A pulsar emits narrow beams of radio waves from the magnetic poles of the neutron star, and the beams sweep around like a lighthouse beacon because the magnetic poles are not aligned with the star's spin axis. If the radio beam misses the Earth, the pulsar cannot be detected by radio telescopes. Fermi's ability to detect so many radio-quiet gamma-ray pulsars indicates that the gamma-rays are emitted in a beam that is wider and more fan-like than the radio beam.
"This favors models in which the gamma rays are emitted from the outer magnetosphere of the pulsar, as opposed to the polar cap much closer to the surface of the star," Saz Parkinson said.
The very intense magnetic and electric fields of a pulsar accelerate charged particles to nearly the speed of light, and these particles are ultimately responsible for the gamma-ray emissions.
Because the rotation of the star powers the emissions, isolated pulsars slow down as they age and lose energy. But a binary companion star can feed material to a pulsar and spin it up to a rotation rate of 100 to 1,000 times a second. These are called millisecond pulsars, and Fermi scientists detected gamma-ray pulsations from eight millisecond pulsars that were previously discovered at radio wavelengths. Those results are reported in a second study also published in the July 2 edition of Science Express.
"Fermi has truly unprecedented power for discovering and studying gamma-ray pulsars," said Paul Ray of the Naval Research Laboratory in Washington. "Since the demise of the Compton Gamma Ray Observatory a decade ago, we've wondered about the nature of unidentified gamma-ray sources it detected in our galaxy. These studies from Fermi lift the veil on many of them."
The corresponding authors of the first paper include Ziegler, Saz Parkinson, Ray, and UCSC graduate student Michael Dormody. Nine of the paper's coauthors are affiliated with UCSC, including William Atwood, adjunct professor of physics, who came up with the original design concept for the LAT as well as the concept for the algorithm to find gamma-ray pulsars. Much of the computational work was carried out on the UCSC Astronomy Department's Pleiades supercomputer. The second paper also has nine coauthors affiliated with UCSC.
Adapted from materials provided by University of California - Santa Cruz.

Mars More Like Earth Than Earth Than Thought? New Details About History Of Water On Red Planet

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ScienceDaily (July 3, 2009) — Scientists offer new details about the history of water on Mars, gleaned from the 2008 NASA Phoenix Mars Mission that was operated from The University of Arizona.

Four papers on the topic have been published in the journal Science on June 3, 2009.
Peter H. Smith, a scientist with the UA Lunar and Planetary Laboratory is the mission's principal investigator. There are 35 co-authors from six countries on the paper. Smith and his group of scientists and students used the lander to investigate the role of water and ice on Mars, as well as the changing weather patterns.
The popular mission launched in early August 2007. In May, 2008, early 10 months later, its landing trajectory was spectacularly captured by the HiRISE camera onboard the Mars Reconnaissance Orbiter.
For the next five months, the UA Science Operations Center clattered with researchers gearing themselves to follow the Martian diurnal phases, which are about 40 minutes longer than day and night on Earth and enough to throw off human sleep schedules in short order.
The landing site was an ejecta field. A comet or asteroid that crashed into the surface melted the ice below creating a sheet of dust and water that flowed across a shallow valley. Smith said that event also covered any large rocks that could have interfered with the ability of the Phoenix to safely land.
Smith and his group found patterns in the ground near the lander, multi-sided shapes about three to ten meters in size. The shapes are created when the surface contracts and the ice cracks. Sand fills in the cracks before the ice expands and buckles the surface to make the distinctive patterns.
Smith used the Phoenix lander's robotic arm to dig a series of trenches to expose subsurface ice and found that the ice in the centers of the polygons was fairly shallow, only a couple of inches deep.
"But in the troughs in between, we went down as much as eight inches and never did find the ice underneath. We weren't able to dig further down because the robot arm was hitting against the side of the lander. It was not known ahead of time that there would be changes in the depth of the ice," he said.
"We wanted to know the origin of the ice," Smith said. "It could have been the remnant of a larger polar ice cap that shrank; could have been a frozen ocean; could have been a snowfall frozen into the ground," he said.
"The most likely theory is that water vapor from the atmosphere slowly diffused into the surface and froze at the level where the temperature matches the frost point. We expected that was probably the source of the ice, but some of what we found was surprising."
One of the surprises was finding perchlorate.
"Perchlorate was not predicted at this landing site and nobody had it on their list of likely chemicals. There was a very high concentration of it, higher than the salts we might have expected like sodium chloride (table salt). As an oxidized state of chlorine, it has interesting properties including a strong affinity for water. On Earth, microbes use it as a chemical energy source."
During the mission, Mars moved from summer to winter, giving Smith and others an unprecedented look at the planet's changing weather patterns, including frost and snow.
"Frost was predicted, but snowfall was quite a welcome surprise," Smith said. "In summer there was a lot of dust in the atmosphere. As we neared fall, the dust cleared, and all of a sudden there were water ice clouds forming at about 4 km (2.5 mi.) above the surface. We could see the clouds scud by, moving through the camera field, and once we saw snow coming out of the bottom of a cloud. It was very exciting to watch the daily weather changes. No one has ever had this experience."
Smith said there are clues that thin films of water modified the soil chemistry. Unlike Earth, Mars has an unstable spin axis, which currently is tilted at about 25 degrees from vertical. Perhaps five millions years ago, he said, it was tilted much more, which would have exposed the north pole to larger amounts of sunlight creating warmer, wetter conditions during summer.
"During that previous climate, you would expect huge increase in the amounts of water vapor coming off the polar cap. If the cap goes unstable, you can have as much as three hundred times as much water in the atmosphere," Smith said.
It would have been enough for snowdrifts. On hot summer days, melting snow could have formed thin films of water.
Not enough for a lake or a river, but he said this could have been a time when damp soil provided a growth period for any microbes that learned to survive those long periods of dryness.
"Who knows? Evolution is a powerful force. If life ever started on Mars, there are niches where still it could survive."
Journal reference:
P. H. Smith et al. H2O at the Phoenix Landing Site. Science, July 3, 2009; Vol. 325. no. 5936, pp. 58 - 61 DOI: 10.1126/science.1172339
Adapted from materials provided by University of Arizona.

Return To The Moon: First Images Kick Off Mapping Mission

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ScienceDaily (July 3, 2009) — NASA's Lunar Reconnaissance Orbiter Camera (LROC) has taken and received its first images of the Moon, kicking off the year-long mapping mission of Earth's nearest celestial neighbor. The LROC imaging system, under the watchful eyes of Arizona State University professor Mark Robison, the principal investigator, consists of two Narrow Angle Cameras (NACs) to provide high-resolution black-and-white images, a Wide Angle Camera (WAC) to provide images in seven color bands over a 60-kilometer (37.28-mile) swath, and a Sequence and Compressor System (SCS) supporting data acquisition for both cameras.

NASA reports that the Lunar Reconnaissance Orbiter, which launched June 18, is performing exceptionally well and spacecraft checkout is proceeding smoothly, so smoothly in fact that LROC was given an early, but short (two orbits) opportunity Tuesday evening to measure temperatures and background values while imaging. Since LRO is in a terminator orbit, much of the area photographed was in shadows, which is actually a good situation for performing engineering checks of camera settings, according to Robinson, with ASU's School of Earth and Space Exploration. Much to the delight of the LROC team, a few of the images captured dramatic views of the surface.
"Our first images were taken along the Moon's terminator – the dividing line between day and night – making us initially unsure of how they would turn out," says Robinson. "Because of the deep shadowing, subtle topography is exaggerated suggesting a craggy and inhospitable surface. In reality, the area is similar to the region where the Apollo 16 astronauts comfortably explored in 1972. Though these images are magnificent in their own right, the main message is that LROC is nearly ready to begin its mission."
LROC NAC: Two details from one of the first images
LRO was 70 kilometers (43.5 miles) above the lunar surface when the summed mode image was taken, resulting in a resolution of approximately 1.4-meters/pixel (34.4°S, 6.0°W). Incredible levels of detail are visible in these two (1000 pixel-by-1000 pixel) cutouts from the full image (2532 pixels-by-53,248 pixels). The NAC data shown has not been calibrated, and the pixel values were stretched to enhance contrast.
Along the terminator, there simply is not much light – the instrument is "photon-starved," resulting in suboptimal signal-to-noise ratios. Without summing, images taken in this circumstance would be underexposed. To compensate for low light levels, the pixels can effectively be made larger by summing adjacent pixels to increase the signal-to-noise ratio, making the image sharper, though with 2x lower resolution. At this resolution, features as small as three meters (9.8 feet) wide can be discerned.
The NAC image shows a starkly beautiful region a few kilometers east of Hell E crater, which is located on the floor of the ancient Imbrian-aged Deslandres impact structure in the lunar highlands south of Mare Nubium. Numerous small, secondary craters can be identified, including several small crater chains. Also identifiable are distinctive lineations made readily apparent by the extreme lighting, representing ejecta from a nearby impact. The quality of these early engineering test images gives the LROC science team confidence it can achieve its primary goals, including obtaining the data needed to support future human lunar exploration and utilization.
Once LRO finishes commissioning operations and enters its 50-kilometer x 50-kilometer (31 miles x 31 miles) mapping orbit, a maneuver currently scheduled for mid-August, the LROC NAC will take images of over 8 percent of the Moon at 50-cm/pixel.
LROC WAC: Seeing the colors of the Moon
The LROC WAC represents a very different type of imaging system than the NAC. The WAC sees the surface in seven colors, one after the other. Looking at the raw image is akin to looking through venetian blinds, which is a little confusing at first.
First you notice the five stair step-like visible bands, and then the two lower-resolution and barely visible ultraviolet bands. During processing, these seven bands are pulled apart and seven single-filter mosaics are created that can be combined in various combinations for scientific analysis.
The WAC is designed to help place the super-high-resolution NAC images into their proper geologic context, as well as discriminate color units on the surface to help geologists map rock types and identify resources. Acquired at the same time as the NAC image, more of the Deslandres region is visible because the WAC has a field of view 20 times wider than the NAC though with substantially lower resolution. For comparison, the width of the NAC image is shown as two vertical bars in the center of the image. The WAC image shown here has not been calibrated and the pixel values were stretched to enhance contrast.
LROC is scheduled for activation July 3 to formally begin its commissioning activities. The LROC Science Operations Center, part of the School of Earth and Space Exploration in the College of Liberal Arts and Sciences on ASU's Tempe campus plans to steadily release images of the lunar frontier as more data is collected and processed.
LRO will spend the next year gathering crucial data on the lunar environment that will help astronauts prepare for exploring the Moon and eventually leaving the Earth-Moon system for voyages to Mars and beyond.
Adapted from materials provided by Arizona State University.

New Class Of Black Holes Discovered

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ScienceDaily (July 2, 2009) — A new class of black hole, more than 500 times the mass of the Sun, has been discovered by an international team of astronomers.

The finding in a distant galaxy approximately 290 million light years from Earth is reported today in the journal Nature.
Until now, identified black holes have been either super-massive (several million to several billion times the mass of the Sun) in the centre of galaxies, or about the size of a typical star (between three and 20 Solar masses).
The new discovery is the first solid evidence of a new class of medium-sized black holes. The team, led by astrophysicists at the Centre d'Etude Spatiale des Rayonnements in France, detected the new black hole with the European Space Agency's XMM-Newton X-ray space telescope.
"While it is widely accepted that stellar mass black holes are created during the death throes of massive stars, it is still unknown how super-massive black holes are formed," says the lead author of the paper, Dr Sean Farrell, now based at the Department of Physics and Astronomy at the University of Leicester.
He added: "One theory is that super-massive black holes may be formed by the merger of a number of intermediate mass black holes. To ratify such a theory, however, you must first prove the existence of intermediate black holes.
"This is the best detection to date of such long sought after intermediate mass black holes. Such a detection is essential. While it is already known that stellar mass black holes are the remnants of massive stars, the formation mechanisms of supermassive black holes are still unknown."
"The identification of HLX-1 is therefore an important step towards a better understanding of the formation of the super-massive black holes that exist at the centre of the Milky Way and other galaxies."
A black hole is a remnant of a collapsed star with such a powerful gravitational field that it absorbs all the light that passes near it and reflects nothing.
It had been long believed by astrophysicists that there might be a third, intermediate class of black holes, with masses between a hundred and several hundred thousand times that of the Sun. However, such black holes had not been reliably detected until now.
This new source, dubbed HLX-1 (Hyper-Luminous X-ray source 1), lies towards the edge of the galaxy ESO 243-49. It is ultra-luminous in X-rays, with a maximum X-ray brightness of approximately 260 million times that of the Sun.
The X-ray signature of HLX-1 and the lack of a counterpart in optical images confirm that it is neither a foreground star nor a background galaxy, and its position indicates that it is not the central engine of the host galaxy.
Using XMM-Newton observations carried out on the 23rd November 2004 and the 28th November 2008, the team showed that HLX-1 displayed a variation in its X-ray signature. This indicated that it must be a single object and not a group of many fainter sources. The huge radiance observed can only be explained if HLX-1 contains a black hole more than 500 times the mass of the Sun. No other physical explanation can account for the data.
S.A.F acknowledges funding from the CNES. S.A.F. and O.G. acknowledge STFC funding. This work made use of the 2XMM Serendipitous Source Catalogue constructed by the XMM-Newton Survey Science Centre on behalf of ESA. We thank the Swift team for performing a TOO observation which provided justification for an additional observation with XMM-Newton. This work was based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.
Adapted from materials provided by University of Leicester, via EurekAlert!, a service of AAAS.

Astronomers Discover Pair Of Solar Systems In The Making

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ScienceDaily (July 2, 2009) — Two University of Hawai'i at Mānoa astronomers have found a binary star-disk system in which each star is surrounded by the kind of dust disk that is frequently the precursor of a planetary system. Doctoral student Rita Mann and Dr. Jonathan Williams used the Submillimeter Array on Mauna Kea, Hawaii to make the observations.

A binary star system consists of two stars bound together by gravity that orbit a common center of gravity. Most stars form as binaries, and if both stars are hospitable to planet formation, it increases the likelihood that scientists will discover Earth-like planets.
This binary system, 253-1536, stands out as the first known example of two optically visible stars, each surrounded by a disk with enough mass to form a planetary system like our own. It lies 1,300 light-years from Earth, in the famous Orion Nebula, the kind of rich cluster of stars that is a common birth environment for most stars in our Milky Way galaxy, including our sun.
One of the disks was discovered in an image taken with the Hubble Space Telescope, but the other disk was hidden in the glare of the star. Hubble saw only the disk shadow, so the amount of material and its capability for planet formation was unknown until the UH team made the SMA observations. "The SMA was able to image the binary system at almost the same level of detail as the Hubble Space Telescope, but in the extreme infrared, where we can see the glow from the dust, rather than its shadow," explained Mann.
The two stars are 400 times farther from each other than Earth is from the sun. They would take 4,500 years, or about the length of human recorded history, to complete one orbit around their common center. Both stars are only about a third the mass of our sun and are much cooler and redder in color. Viewed from a potential future planet, the stellar neighbor would appear as an intense point in the night sky, about one thousand times brighter than the brightest star in our night sky, Sirius. Planets around the other star would be visible only through telescopes, but they would be within reach of spacecraft from a civilization with the same level of technology as ours.
The larger disk in 253-1536 is also the most massive found in the Orion Nebula so far. The discovery of this massive disk and the binary disk system improve our understanding of how common planet formation is in our Galaxy and place our Solar System in context.
Journal reference:
Mann et al. Massive Protoplanetary Disks in Orion beyond the Trapezium Cluster. The Astrophysical Journal, 2009; 699 (1): L55 DOI: 10.1088/0004-637X/699/1/L55
Adapted from materials provided by University of Hawaii at Manoa, via EurekAlert!, a service of AAAS.

First Direct Evidence Of Lightning On Mars Detected

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ScienceDaily (July 1, 2009) — For the first time, direct evidence of lightning has been detected on Mars, say University of Michigan researchers who found signs of electrical discharges during dust storms on the Red Planet.

The bolts were dry lightning, says Chris Ruf, a professor in the departments of Atmospheric, Oceanic and Space Sciences and Electrical Engineering and Computer Sciences.
"What we saw on Mars was a series of huge and sudden electrical discharges caused by a large dust storm," Ruf said. "Clearly, there was no rain associated with the electrical discharges on Mars. However, the implied possibilities are exciting."
Electric activity in Martian dust storms has important implications for Mars science, the researchers say.
"It affects atmospheric chemistry, habitability and preparations for human exploration. It might even have implications for the origin of life, as suggested by experiments in the 1950s," said Nilton Renno, a professor in the Department of Atmospheric, Oceanic and Space Sciences.
The findings are based on observations made using an innovative microwave detector developed at the U-M Space Physics Research Laboratory. The kurtosis detector, which is capable of differentiating between thermal and non-thermal radiation, took measurements of microwave emissions from Mars for approximately five hours a day for 12 days between May 22 and June 16, 2006.
On June 8, 2006 both an unusual pattern of non-thermal radiation and an intense Martian dust storm occurred, the only time that non-thermal radiation was detected. Non-thermal radiation would suggest the presence of lightning.
The researchers reviewed the data to determine the strength, duration and frequency of the non-thermal activity, as well as the possibility of other sources. But each test led to the conclusion that the dust storm likely caused dry lightning.
This work confirms soil measurements from the Viking landers 30 years ago, and it challenges 2006 experiments that suggested otherwise.
Data from the Viking landers raised the possibility that Martian dust storms might be electrically active like Earth's thunderstorms and thus, might be a source of reactive chemistry. But the hypothesis was untestable. In 2006, using theoretical modeling, laboratory experiments and field studies on Earth, a group of planetary scientists suggested that there was no direct evidence that lightning occurred on Mars. This new research refutes those findings.
"Mars continues to amaze us. Every new look at the planet gives us new insights," said Michael Sanders, manager of the exploration systems and technology office at Jet Propulsion Laboratory and a researchers involved in this study.
The new finding will be published in an upcoming issue of Geophysical Research Letters. The paper is called "The Emission of Non-Thermal Microwave Radiation by a Martian Dust Storm." In addition to Ruf and Renno, other U-M authors include Jasper Kok, a recent Ph.D. graduate from the Department of Atmospheric, Oceanic and Space Sciences; Etienne Bandelier, a graduate student in the same department; and Steve Gross, a lead research engineer in the same department.
Adapted from materials provided by University of Michigan.

Intense Heat Killed The Universe's Would-be Galaxies, Researchers Say

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ScienceDaily (July 1, 2009) — Millions of would-be galaxies failed to develop after being exposed to intense heat from the first stars and black holes formed in the early Universe, according to new research. Our Milky Way galaxy only survived because it was already immersed in a large clump of dark matter which trapped gases inside it, scientists led by Durham University's Institute for Computational Cosmology (ICC) found.

The research, presented at an international conference on July 1, 2009 also forms a core part of a new ICC movie charting the evolution of the Milky Way to be shown at the Royal Society.
The researchers said that the early Milky Way, which had begun forming stars, held on to the raw gaseous material from which further stars would be made. This material would otherwise have been evaporated by the high temperatures generated by the "ignition" of the Universe about half-a-billion years after the Big Bang.
Tiny galaxies, inside small clumps of dark matter, were blasted away by the heat which reached approximate temperatures of between 20,000 and 100,000 degrees centigrade, the scientists, including experts at Japan's University of Tsukuba, said.
Dark matter is thought to make up 85 per cent of the Universe's mass and is believed to be one of the building blocks of galaxy formation.
Using computer simulations carried out by the international Virgo Consortium (which is led by Durham) the scientists examined why galaxies like the Milky Way have so few companion galaxies or satellites.
Astronomers have found a few dozen small satellites around the Milky Way, but the simulations revealed that hundreds of thousands of small clumps of dark matter should be orbiting our galaxy.
The scientists said the heat from the early stars and black holes rendered this dark matter barren and unable to support the development of satellite star systems.
The findings will be presented to The Unity of the Universe conference to be held at the Institute of Cosmology and Gravitation, at the University of Portsmouth on Wednesday, July 1. The work has been funded by the Science and Technology Facilities Council (STFC) and the Japanese Society for the Promotion of Science.
The simulations also form part of a new ICC movie – called Our Cosmic Origins – which combines ground-breaking simulations with observations of galaxies to track the evolution of the Milky Way over the 13-billion-year history of the Universe.
Joint lead investigator Professor Carlos Frenk, Director of the Institute for Computational Cosmology, at Durham University, said: "The validity of the standard model of our Universe hinges on finding a satisfactory explanation for why galaxies like the Milky Way have so few companions.
"The simulations show that hundreds of thousands of small dark matter clumps should be orbiting the Milky Way, but they didn't form galaxies.
"We can demonstrate that it was almost impossible for these potential galaxies to survive the extreme heat generated by the first stars and black holes.
"The heat evaporated gas from the small dark matter clumps, rendering them barren. Only a few dozen front-runners which had a head start on making stars before the Universe ignited managed to survive."
By providing a natural explanation for the origin of galaxies, the simulations support the view that cold dark matter is the best candidate for the mysterious material believed to make up the majority of our Universe, the scientists added.
It is now up to experimental physicists to either find this dark matter directly or to make it in a particle accelerator such as the Large Hadron Collider at CERN.
Professor Frenk, added: "Identifying the dark matter is not only one of the most pressing problems in science today, but also the key to understanding the formation of galaxies."
Joint lead investigator Dr Takashi Okamoto from the University of Tsukuba said: "These are still early days in trying to make realistic galaxies in a computer, but our results are very encouraging."
Presentations:
1. Constraining feedback in galaxy formation: cosmological simulations of satellite galaxy formation, Okamoto, T; Frenk CS; Jenkins A; and Theuns T, July 2009.
2. The origin of failed subhaloes and the common mass scale of the Milky Way satellite galaxies, Okamoto, T and Frenk CS, July 2009.
Adapted from materials provided by Durham University, via EurekAlert!, a service of AAAS.