NASA's Fermi Spots 'Superflares' in the Crab Nebula

The famous Crab Nebula supernova remnant has erupted in an enormous flare five times more powerful than any flare previously seen from the object. On April 12, NASA's Fermi Gamma-ray Space Telescope first detected the outburst, which lasted six days.

The nebula is the wreckage of an exploded star that emitted light which reached Earth in the year 1054. It is located 6,500 light-years away in the constellation Taurus. At the heart of an expanding gas cloud lies what is left of the original star's core, a superdense neutron star that spins 30 times a second. With each rotation, the star swings intense beams of radiation toward Earth, creating the pulsed emission characteristic of spinning neutron stars (also known as pulsars).

Apart from these pulses, astrophysicists believed the Crab Nebula was a virtually constant source of high-energy radiation. But in January, scientists associated with several orbiting observatories, including NASA's Fermi, Swift and Rossi X-ray Timing Explorer, reported long-term brightness changes at X-ray energies.

"The Crab Nebula hosts high-energy variability that we're only now fully appreciating," said Rolf Buehler, a member of the Fermi Large Area Telescope (LAT) team at the Kavli Institute for Particle Astrophysics and Cosmology, a facility jointly located at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University.

Since 2009, Fermi and the Italian Space Agency's AGILE satellite have detected several short-lived gamma-ray flares at energies greater than 100 million electron volts (eV) -- hundreds of times higher than the nebula's observed X-ray variations. For comparison, visible light has energies between 2 and 3 eV.

On April 12, Fermi's LAT, and later AGILE, detected a flare that grew about 30 times more energetic than the nebula's normal gamma-ray output and about five times more powerful than previous outbursts. On April 16, an even brighter flare erupted, but within a couple of days, the unusual activity completely faded out.

"These superflares are the most intense outbursts we've seen to date, and they are all extremely puzzling events," said Alice Harding at NASA's Goddard Space Flight Center in Greenbelt, Md. "We think they are caused by sudden rearrangements of the magnetic field not far from the neutron star, but exactly where that's happening remains a mystery."

The Crab's high-energy emissions are thought to be the result of physical processes that tap into the neutron star's rapid spin. Theorists generally agree the flares must arise within about one-third of a light-year from the neutron star, but efforts to locate them more precisely have proven unsuccessful so far.

Since September 2010, NASA's Chandra X-ray Observatory routinely has monitored the nebula in an effort to identify X-ray emission associated with the outbursts. When Fermi scientists alerted astronomers to the onset of a new flare, Martin Weisskopf and Allyn Tennant at NASA's Marshall Space Flight Center in Huntsville, Ala., triggered a set of pre-planned observations using Chandra.

"Thanks to the Fermi alert, we were fortunate that our planned observations actually occurred when the flares were brightest in gamma rays," Weisskopf said. "Despite Chandra's excellent resolution, we detected no obvious changes in the X-ray structures in the nebula and surrounding the pulsar that could be clearly associated with the flare."

Scientists think the flares occur as the intense magnetic field near the pulsar undergoes sudden restructuring. Such changes can accelerate particles like electrons to velocities near the speed of light. As these high-speed electrons interact with the magnetic field, they emit gamma rays.

To account for the observed emission, scientists say the electrons must have energies 100 times greater than can be achieved in any particle accelerator on Earth. This makes them the highest-energy electrons known to be associated with any cosmic source. Based on the rise and fall of gamma rays during the April outbursts, scientists estimate that the size of the emitting region must be comparable in size to the solar system.

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

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

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New sensor developed by MIT chemical engineers can detect tiny traces of explosives

MIT researchers have created a new detector so sensitive it can pick up a single molecule of an explosive such as TNT.

To create the sensors, chemical engineers led by Michael Strano coated carbon nanotubes — hollow, one-atom-thick cylinders made of pure carbon — with protein fragments normally found in bee venom. This is the first time those proteins have been shown to react to explosives, specifically a class known as nitro-aromatic compounds that includes TNT.

If developed into commercial devices, such sensors would be far more sensitive than existing explosives detectors — commonly used at airports, for example — which use spectrometry to analyze charged particles as they move through the air.

“Ion mobility spectrometers are widely deployed because they are inexpensive and very reliable. However, this next generation of nanosensors can improve upon this by having the ultimate detection limit, [detecting] single molecules of explosives at room temperature and atmospheric pressure,” says Strano, the Charles (1951) and Hilda Roddey Career Development Associate Professor of Chemical Engineering.

A former graduate student in Strano’s lab, Daniel Heller (now a Damon Runyon Fellow at MIT’s David H. Koch Institute for Integrative Cancer Research), is lead author of a paper describing the technology in the Proceedings of the National Academy of Sciences. The paper appears online this week.

A unique fingerprint

Strano has filed for a patent on the technology, which makes use of protein fragments called bombolitins. “Scientists have studied these peptides, but as far as we know, they’ve never been shown to have an affinity for and recognize explosive molecules in any way,” he says.

In recent years, Strano’s lab has developed carbon-nanotube sensors for a variety of molecules, including nitric oxide, hydrogen peroxide and toxic agents such as the nerve gas sarin. Such sensors take advantage of carbon nanotubes’ natural fluorescence, by coupling them to a molecule that binds to a specific target. When the target is bound, the tubes’ fluorescence brightens or dims.

The new explosives sensor works in a slightly different way. When the target binds to the bee-venom proteins coating the nanotubes, it shifts the fluorescent light’s wavelength, instead of changing its intensity. The researchers built a new type of microscope to read the signal, which can’t be seen with the naked eye. This type of sensor, the first of its kind, is easier to work with because it is not influenced by ambient light.

“For a fluorescent sensor, using the intensity of the fluorescent light to read the signal is more error-prone and noisier than measuring a wavelength,” Strano says.

Each nanotube-peptide combination reacts differently to different nitro-aromatic compounds. By using several different nanotubes coated in different bombolitins, the researchers can identify a unique “fingerprint” for each explosive they might want to detect. The nanotubes can also sense the breakdown products of such explosives.

“Compounds such as TNT decompose in the environment, creating other molecule types, and those derivatives could also be identified with this type of sensor,” Strano says. “Because molecules in the environment are constantly changing into other chemicals, we need sensor platforms that can detect the entire network and classes of chemicals, instead of just one type.”

The researchers also showed that the nanotubes can detect two pesticides that are nitro-aromatic compounds as well, making them potentially useful as environmental sensors. The research was funded by the Institute for Soldier Nanotechnologies at MIT.

Philip Collins, a professor of physics at the University of California at Irvine, says the new approach is a novel extension of Strano’s previous work on carbon-nanotube sensors. “It’s nice what they’ve done — combined a couple of different things that are not sensitive to explosives, and shown that the combination is sensitive,” says Collins, who was not involved in this research.

The technology has already drawn commercial and military interest, Strano says. For the sensor to become practical for widespread use, it would have to be coupled with a commercially available concentrator that would bring any molecules floating in the air in contact with the carbon nanotubes.

“It doesn’t mean that we are ready to put these onto a subway and detect explosives immediately. But it does mean that now the sensor itself is no longer the bottleneck,” Strano says. “If there’s one molecule in a sample, and if you can get it to the sensor, you can now detect and quantify it.”

Other researchers from MIT involved in the work include former postdocs Nitish Nair and Paul Barone; graduate students Jingqing Zhang, Ardemis Boghossian and Nigel Reuel; George Pratt ’10 and junior Adam Hansborough.

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Researchers get new view of how water and sulfur dioxide mix

The role of sulfur dioxide -- a pollutant of volcanic gasses and many combustion processes -- in acid rain is well known, but how sulfur dioxide reacts at the surface of aqueous particulates in the atmosphere to form acid rain is far from understood.

In National Science Foundation-funded laboratory experiments at the UO, chemistry doctoral student Stephanie T. Ota examined the behavior of sulfur dioxide as it approaches and adsorbs onto water at low temperatures that mimic high-atmospheric conditions. Using a combination of short-pulsed infrared and visible laser beams, she monitored the interaction of sulfur dioxide with water as it is flowed over a water surface.

The results -- detailed online ahead of regular publication in the Journal of the American Chemical Society -- show that as sulfur dioxide molecules approach the surface of water, they are captured by the top-most surface water molecules, an effect that is enhanced at cold temperatures.

Although this reaching out, says co-author Geraldine L. Richmond, professor of chemistry, provides a doorway for sulfur dioxide to enter the water solution, the weak nature of the surface-bonding interaction doesn't guarantee that the water temptress will be successful.

"We have found that that the sulfur dioxide bonding to the surface is highly reversible and does not necessarily provide the open doorway that might be expected," Ota said. "For example, for highly acidic water, the sulfur dioxide approaches and bonds to the water surface but shows little interest in going any further into the bulk water."

The uptake of gases like sulfur dioxide has important implications in understanding airborne pollutants and their role in global warming and climate change. Sulfur dioxide that has come together with water, becoming aqueous, reflects light coming toward the planet, while carbon dioxide accumulating in the atmosphere traps heat onto the planet.

Understanding the interaction of surface water molecules, such as those in clouds and fog, with pollutants rising from human activity below may help scientists better predict potential chemical reactions occurring in the atmosphere and their impacts, said Richmond, who was elected May 3 as a member of the National Academy of Sciences.

"In the past we presumed that most chemistry in the atmosphere occurred when gas molecules collide and react," she said. "These studies are some of the first to provide molecular insights into what happens when an atmospherically important gas such as sulfur dioxide collides with a water surface, and the role that water plays in playing the temptress to foster reactivity."

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The Life of an Ant

livescience.com

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Zoologger: Flashmob gathering of world's largest fish

Species: Rhincodon typus

Habitat: all tropical and warm temperate seas, except the Mediterranean, being large and enigmatic

On 12 August 2009 a small team of scientists took a light plane over the Caribbean Sea, just off Mexico's Yucatán peninsula. To their astonishment they saw 420 whale sharks swimming together in 18 square kilometres of ocean. It was by far the largest group ever seen (see photo).

Whale sharks are the biggest fish alive, regularly reaching 10 metres long and sometimes growing to 12 metres – and possibly even more. They dwarf the largest bony fish, the ocean sunfish, which does not even reach 2 metres.

But despite their size they remain mysterious. No one even knows how or where they breed.

Whale shark of a time

Alistair Dove of the Georgia Aquarium in Atlanta led the survey that spotted the whale shark flashmob. The team had found similar but smaller gatherings in 2006 and 2008, but seeing more than 400 whale sharks together came as a surprise, because they normally swim alone and only come together in groups of a few dozen.

The animals spent almost all their time together feeding on dense clusters of eggs laid by Atlantic little tunny, a fish related to tuna. The sharks mostly fed at the surface, swimming forwards with their top jaws above the water and sucking in floating tunny eggs. Confronted with particularly rich patches, they stopped and hung almost vertically with their heads up, sucking in huge gulps of water and food.

It's unclear how the sharks found the feeding ground. Rather than detecting it themselves, they might have followed other fish.

Certainly they are no strangers to long-distance travel, often crossing entire oceans. In 2007 70 whale sharks from around the world had their DNA analysed, and the most common genetic marker was found in fish from every quarter. Far from sticking to just one ocean, whale sharks are cosmopolitan.

Getting together

But whereas marine mammals like whales take advantage of gatherings to socialise and find mates, the whale sharks were peculiarly antisocial. "It appears they were not gathering to interact with each other," Dove says, "but were simply converging on a particularly rich food source."

Dove has studied captive whale sharks and says there is little evidence of any social system, such as a dominance hierarchy. But he says different sharks do have identifiable behaviour patterns, which suggests that, like many animals, they have at least the beginnings of personality.

A recent study showed that whale shark brains are relatively small for their body size, suggesting they are fairly dim and don't have complex social lives – social behaviour tends to be correlated with brain size in other animals. However, they also have a fairly large pallium – the part of the brain that, in humans, develops into the cerebral cortex and is the key to our intelligence.

Even if their social lives are simple, they must get together at some point to mate – though no one has ever seen them do it. The females give birth to live young, and one pregnant female nicknamed "megamamma" was found to be carrying 300 embryos.

Dove suspects they mate in the same way as other sharks: the mating pair stop swimming and partially entwine their bodies while the male inserts his genital clasper into the female from the side. As Dove says, "Two adult whale sharks sinking into the depths locked in a breeding embrace must be quite a sight."

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0018994

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The 10 Biggest Insects In The World

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Report sees sharper sea rise from Arctic melt

The findings "emphasize the need for greater urgency" in combating global warming, says the report of the Arctic Monitoring and Assessment Program (AMAP), the scientific arm of the eight-nation Arctic Council.

The warning of much higher seas comes as the world's nations remain bogged down in their two-decade-long talks on reducing emissions of carbon dioxide and other greenhouse gases blamed for global warming.

Rising sea levels are expected to cause some of global warming's worst damage - from inundated small islands to possible flooding of New York City's subways. Oceans will not rise uniformly worldwide, because of currents, winds and other factors, but such low-lying areas as Bangladesh and Florida will likely be hard-hit.

The new report, whose executive summary was obtained by The Associated Press, is to be delivered to U.S. Secretary of State Hillary Rodham Clinton and foreign ministers of the other seven member nations at an Arctic Council meeting next week in Greenland. It first will be discussed by some 400 international scientists at a conference this week in Copenhagen, Denmark.

Drawing on improved research techniques and recent scientific papers, the AMAP report updates forecasts made by the U.N.'s expert panel on climate change in its last major assessment in 2007.

The melting of Arctic glaciers and ice caps, including Greenland's massive ice sheet, is projected to help raise global sea levels by 35 to 63 inches (90 to 160 centimeters) by 2100, AMAP said, although it noted that estimate was highly uncertain.

That's up from the 2007 projection of 7 to 23 inches (19 to 59 centimeters) by the U.N. panel. The U.N. group had left out the possible acceleration of melting in Greenland and Antarctica, saying research on that hadn't advanced sufficiently by the mid-2000s. The U.N. estimate was based largely on the expansion of ocean waters from warming and the runoff from melting land glaciers elsewhere in the world.

Now the AMAP assessment finds that Greenland was losing ice in the 2004-2009 period four times faster than in 1995-2000.

In addition, the cover of sea ice on the Arctic Ocean is shrinking faster than projected by the U.N. panel, threatening the long-term survival of polar bears and other ice-dependent species. Summer ice coverage has been at or near record lows every year since 2001, said AMAP, predicting the ocean will be almost ice-free in the summer in 30 to 40 years.

Arctic temperatures in the past six years were the highest since measurements began in 1880, and "feedback" mechanisms are believed to be speeding up warming in the far north.

One such mechanism involves the ocean absorbing more heat when it's not covered by ice, because ice reflects the sun's energy. That effect has been anticipated by scientists "but clear evidence for it has only been observed in the Arctic in the past five years," AMAP said.

It projected that average fall and winter temperatures in the Arctic will climb by roughly 5 to 11 degrees Fahrenheit by 2080, even if greenhouse gas emissions are lower than in the past decade.

"The observed changes in sea ice on the Arctic Ocean, in the mass of the Greenland ice sheet and Arctic ice caps and glaciers over the past 10 years are dramatic and represent an obvious departure from the long-term patterns," AMAP said.

A leading American ice specialist, Richard Alley of Pennsylvania State University, who did not take part in the AMAP assessment, agreed that recent scientific estimates generally support its central finding.

A sea level rise of more than 3 feet this century "fits well within these estimates, and a somewhat higher value cannot be excluded," Alley said.

Scientists have steadily improved ways of measuring the loss of ice into the oceans.

In research reported in March in the journal Geophysical Research Letters, U.S. and European scientists used two independent methods to corroborate their findings: the on-the-ground measurement of ice thickness and movements using GPS stations and other tools, and the measurement of ice mass through gravity readings from satellites.

Led by Eric Rignot of NASA's Jet Propulsion Laboratory, they calculated that the accelerating melt of the vast Greenland and Antarctic ice sheets would contribute to an overall sea-level rise of some 13 inches by 2050. They didn't project sea levels to 2100 because of long-range uncertainties, but their work, like AMAP's, significantly updates previous projections.

The AMAP report said melting glaciers and ice sheets worldwide have become the biggest contributor to sea level rise. Greenland's ice sheet alone accounted for more than 40 percent of the 0.12 inches (3.1 millimeters) of sea-level rise observed annually between 2003 and 2008, AMAP said.

The AMAP group's main function is to advise the nations surrounding the Arctic - the U.S., Canada, Russia, Denmark, Norway, Sweden, Iceland and Finland - on threats to its environment.

The updated projections should supply further scientific ammunition in the uphill struggle for concerted global action to rein in greenhouse emissions. The failure of emissions-capping legislation in the U.S. Congress last year was one major setback.

"I'm not sure what is more alarming, the glacial pace of Congress to reduce carbon pollution or the astounding rate of melting Arctic ice," Lou Leonard, climate chief at the World Wildlife Fund, said of the new report.

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