Wednesday, October 1, 2008

A Star That Bursts, Blinks and Disappears

Artist concept of a magnetar flare
This illustration shows a flare from magnetar Swift J195509+261406. A starquake is probably what triggered the object's 40 optical flares. Credit: NASA/Swift/Sonoma State University/A. Simonnet

"Twinkle, twinkle little star" goes the nursery rhyme. Now, astronomers are reporting on a strange case where one of the littlest of stars "twinkled" with gamma rays, X-rays, and light -- and then vanished.

The story began on June 6, 2007. That’s when a spike of gamma-rays lasting less than five seconds washed over NASA's Swift satellite. But this high-energy flash wasn't a gamma-ray burst -- the birth cry of a black hole far across the universe. It was something much closer to home.

Swift immediately reported the event’s position to astronomers all over the world. Within a minute, robotic telescopes turned to a spot in the constellation Vulpecula. Because Swift found an X-ray glow coming from this point, astronomers cataloged the object as "Swift J195509+261406," after its position in the sky and the discovering satellite. (Well, they had to call it something!)

During the next three days, the object brightened and faded in visible light. Not once, not twice -- but 40 times! Eleven days later, it flashed again, this time at infrared wavelengths. Then, it disappeared from view.

"I love it when Swift enables a discovery like this," says Neil Gehrels, the mission's lead scientist at NASA Goddard Space Flight Center in Greenbelt, Md. "The observatory is an astronomical robot built for gamma-ray burst studies, but it can also quickly point at other bizarre objects with bright flares."

Astronomers think the object was a neutron star -- the crushed innards of a massive star that long ago exploded as a supernova -- about 15,000 light-years away. Writing in the Sept. 25 issue of the science journal Nature, a team of 42 scientists concludes that Swift J195509+261406 is a special type of neutron star called a magnetar.

"We are dealing with an object that was hibernating for decades before entering a brief activity period," explains Alberto J. Castro-Tirado, lead author of the paper. "Magnetars remain quiet for decades."

Although measuring only about 12 miles across -- about the size of a city -- neutron stars have the strongest magnetic fields in the cosmos. Sometimes, those magnetic fields are super strong -- more than 100 times the strength of typical neutron stars.

Astronomers put these magnetic monsters in their own class: magnetars. Only about a dozen magnetars are known, but scientists suspect our galaxy contains many more. We just don’t see them because they’re quiet most of the time.

So what happened last year? Why did this previously unseen star begin behaving so badly? And why did it stop?

Combine a magnetar's pumped-up magnetic field with its rapid spin, and sooner or later something has to give. Every now and then, the magnetar’s rigid crust snaps under the strain.

This "starquake" releases pent-up magnetic energy, which creates bursts of light and radiation. Once the star’s crust and magnetic field settle down, the star goes dark and disappears from our view. At least until the next quake.

Astronomers suspect that magnetars lose their punch as time passes, but Swift J195509+261406 provides the missing link between objects exhibiting regular activity and those that have settled into retirement -- and invisibility.

So twinkle, twinkle magnetar. That's how we'll learn just where you are.

Related link:

> NASA's Swift Web site
Francis Reddy
NASA's Goddard Space Flight Center

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Pictured: The amazing natural wonders captured by the world's best photographers

By Claire Bates

A black-striped cleaner fish tentatively grooms a bullethead parrotfish ten times its size off the Red Sea.

In another stunning photograph a mass of swirling starlings create the illusion of a giant bird in flight.

Birds are also featured in a mind-boggling portrait of a heaving sandpiper congregation, resting before their great migration.

These extraordinary images are among those submitted by finalists for the Wildlife Photographer of the Year 2008 competition.

The annual event is an international showcase for the best photography featuring natural subjects. The finalists will exhibited at the Natural History Museum from the end of October.

Fish off the coast of Eilat, Israel, get a quick clean from smaller fish that pick off parasites

The fish photograph was taken by Noam Kortler from Israel and was highly commended in the category 'The Underwater World'.

He had captured life at Moses Rock, near Eilat, where most big reef fish make a point of turning for a daily grooming session from cleaner fish, who pick off parasites.

The cleaner fish advertise their identity and their services with their black-striped livery and a special jerky swim.

The stunning sandpiper image was made by Arthur Morris who caught on camera more than 6,000 sandpipers in the Alaskan fishing town of Cordova.

He flew to the town in early May when he knew flocks were likely to be at their peak, but was disappointed when told he had missed the peak of migration by just one week.

A congregation of sandpipers in Canada. Birds are among the most popular subjects in the competition

Mr Morris was told there may be a few birds on a sandbar near town but when he arrived he found a snoozing congregation of western sandpipers, and got his magical snap.

His image was highly commended in the category Animal Behaviour: Birds, which is one of the most popular categories.


Starlings gather in the sky above Lake Morgan in Turkey to form the shape of a giant bird

Another stunning image from this field was taken by Baris Koca at Lake Mogan, near Ankara in Turkey. The photographer had tried to capture the amazing shape-shifting of the flocks of starlings coming in to roost for days. But none of his attempts did the spectacle justice.

Then one weekend when he was standing on the frozen lake with the sun behind him, the thousand-strong flocks of starlings wheeled in over the horizon to merge into a dense super-flock, which for a second formed the shape of a giant bird in flight, and the moment was captured.

Another category called 'In Praise of Plants' showcases the beauty and importance of flowering and non-flowering plants.

Darran Leal saw this close-up image he took in Queensland as a symbol of renewal in an area hit by a cyclone

Darran Leal captured his beautiful image after he explored the rainforest in the far north of Queensland in Australia, a year after Cyclone Larry had decimated vast areas in 2006.

He came across a small tree backlit by the sun and sparkling with rain among the ruins.

'A jewel-like drop, with its perfect reflection of leaves inside, struck me as a great symbol of the regrowth of the rainforest, but I had to move fast,' Darran said.

'The challenge was to capture the moment in spite of gusts of wind and the great magnification required.'

The spectacular images were picked from 32,351 photographs from 82 countries, which were entered into the popular open contest.

The competition is run by the NHM and BBC Wildlife Magazine and winners from 17 categories, including three for photographers under 18, will be announced at the exhibition launch.

The Wildlife Photographer Of The Year will run from 31 October 2008 - 26 April 2009

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Australians urged to eat kangaroo

Baby kangaroo and mother
Kangaroos have a different digestive system to cows and sheep

An Australian government adviser on climate change has urged Australians to ditch beef and lamb for kangaroo steaks to help save the planet.

Sheep and cows produce a high amount of environmentally unfriendly methane gas through belching and flatulence.

But economist Ross Garnaut noted in a report on global warming that kangaroos produce virtually no methane.

He predicts a change in farming and eating habits with the introduction of a national carbon trading scheme.

In a 600-page study commissioned by the Australian government, Professor Garnaut calls for the agricultural industry to be included in the emissions trading scheme to be set up by 2010.

This would mean landowners would have to buy permits for their greenhouse gas emissions if they go beyond the recommended limits.

Pet food

The higher costs of farming sheep and cattle and their vulnerability to the effects of climate change, including water scarcity, could hasten a transition toward greater production of lower-emitting forms of meat, Prof Garnaut believes.

And he thinks kangaroos, which have a different digestive system to cows and sheep, could hold the key.

"For most of Australia's human history - around 60,000 years - kangaroo was the main source of meat. It could again become important," he said.

Citing a study for the potential of kangaroos to replace other livestock for meat production, he notes that by 2020 beef cattle could be reduced by 7 million and sheep by 36 million.

This would create the opportunity for an increase in kangaroo numbers from 34 million to 240 million in 12 years time.

That amount would be more than enough to replace the lost beef and lamb production, while also being more profitable for farmers as emissions permit prices rise.

While popular in a number of countries, in Australia eating kangaroo - the country's national symbol - is still controversial and the meat is largely used in pet food.

But many health-conscious Australians have been won over by its lean red meat.

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Earth's Air Divided by Chemical Equator

By Andrea Thompson