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Fri 18 Feb, 2005 03:40 pm
AFP
Monster star burst was brighter than full Moon: astronomers
2 hours, 10 minutes ago
PARIS (AFP) - Stunned astronomers described the greatest cosmic explosion ever monitored -- a star burst from the other side of the galaxy that was briefly brighter than the full Moon and swamped satellites and telescopes.
The high-radiation flash, detected last December 27, caused no harm to Earth but would have literally fried the planet had it occurred within a few light years of home.
Normally reserved skywatchers struggled for superlatives.
"This is a once-in-a-lifetime event," said Rob Fender of Britain's Southampton University.
"We have observed an object only 20 kilometers (12 miles) across, on the other side of our galaxy, releasing more energy in a 10th of a second than the Sun emits in 100,000 years."
"It was the mother of all magnetic flares -- a true monster," said Kevin Hurley, a research physicist at the University of California at Berkeley.
Bryan Gaensler of the United States' Harvard-Smithsonian Center for Astrophysics, described the burst as "maybe a once per century or once per millennium event in our galaxy.
"Astronomically speaking, this explosion happened in our backyard. If it were in our living room, we'd be in big trouble."
The blast was caused by an eruption on the surface of a known, exotic kind of neutron star called SGR 1806-20, located about 50,000 light years from Earth in the constellation of Sagittarius and about three billion times farther from us than the Sun.
A neutron star is the remnant of a very large star near the end of its life -- a tiny, extraordinarily dense core with a powerful magnetic field, spinning swiftly on its axis.
When these ancient star cores finally run out of fuel, they collapse in on themselves and explode as a supernova.
There are millions of neutron stars in the Milky Way but, so far, only a dozen have been found to be "magnetars": neutron stars with an ultra-powerful magnetic field.
Magnetars have have a magnetic field measuring about 1,000 trillion gauss, hundreds of times more powerful than that of any other object in the Universe.
To give an idea of this in earthly terms, the field is so powerful that it could strip the data off a credit card at a distance of 200,000 kilometers (120,000 miles).
SGR 1806-20 is an even rarer bird. It is one of only four known "soft gamma repeater" (SGR) magnetars, so called because they flare up randomly and release gamma rays in a mammoth burst.
Why this happens is unknown. One theory is that the energy release comes from magnetic fields which wrestle and overlap because of the star's spin and then snap back and reconnect, creating a "starquake" rather like the competing faults that cause an earthquake.
What is sure, though, is that the outpouring of energy is massive.
The SGR 1806-20 spewed out about 10,000 trillion trillion watts, or about 100 times brighter than any of the several "giant flares" that have been previously recorded.
Despite this energy loss, the strange star did not even pause, Britain's Royal Astronomical Society (RAS) said.
"SGR 1806-20 spins once in only 7.5 seconds. Amazingly, the December 27 event did not cause any slowing of its spin rate, as would be expected," the RAS said.
The flare, detected by satellites and telescopes operated by NASA (news - web sites) and Europe, was so powerful that it bounced off the Moon and lit up the Earth's upper atmosphere. For over a tenth of the second, it was actually brighter than a full Moon, and briefly overwhelmed delicate sensors, RAS said.
Two science teams, formed by observations provided by 20 institutes around the world, will report on the blast in a forthcoming issue of the British weekly journal Nature.
Many questions will be thrown up by the event, including the intriguing speculation that the dinosaurs may have been wiped out by a similar, closer gamma-ray explosion 65 million years ago, and not by climate change inflicted by an asteroid impact.
"Had this happened within 10 light years of us, it would have severly damaged our atmosphere and possibly have triggered a mass extinction," said lead-author Gaensler.
The good news, he noted, is that the nearest known magnetar to Earth, 1E 2259+586, is about 13,000 light years away.
Same story --- diffent source
Science - Space.com
SPACE.com
Brightest Galactic Flash Ever Detected Hits Earth
1 hour, 14 minutes ago
Robert Roy Britt
Senior Science Writer
SPACE.com
A huge explosion halfway across the galaxy packed so much power it briefly altered Earth's upper atmosphere in December, astronomers said Friday.
No known eruption beyond our solar system has ever appeared as bright upon arrival.
But you could not have seen it, unless you can top the X-ray vision of Superman: In gamma rays, the event equaled the brightness of the full Moon's reflected visible light.
The blast originated about 50,000 light-years away and was detected Dec. 27. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers).
The commotion was caused by a special variety of neutron star known as a magnetar. These fast-spinning, compact stellar corpses -- no larger than a big city -- create intense magnetic fields that trigger explosions. The blast was 100 times more powerful than any other similar eruption witnessed, said David Palmer of Los Alamos National Laboratory, one of several researchers around the world who monitored the event with various telescopes.
"Had this happened within 10 light-years of us, it would have severely damaged our atmosphere and possibly have triggered a mass extinction," said Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics (CfA).
There are no magnetars close enough to worry about, however, Gaensler and two other astronomers told SPACE.com. But the strength of the tempest has them marveling over the dying star's capabilities while also wondering if major species die-offs in the past might have been triggered by stellar explosions.
'Once-in-a-lifetime'
The Sun is a middle-aged star about 8 light-minutes from us. It's tantrums, though cosmically pitiful compared to the magnetar explosion, routinely squish Earth's protective magnetic field and alter our atmosphere, lighting up the night sky with colorful lights called aurora.
Solar storms also alter the shape of Earth's ionosphere, a region of the atmosphere 50 miles (80 kilometers) up where gas is so thin that electrons can be stripped from atoms and molecules -- they are ionized -- and roam free for short periods. Fluctuations in solar radiation cause the ionosphere to expand and contract.
"The gamma rays hit the ionosphere and created more ionization, briefly expanding the ionosphere," said Neil Gehrels, lead scientist for NASA (news - web sites)'s gamma-ray watching Swift observatory.
Gehrels said in an email interview that the effect was similar to a solar-induced disruption but that the effect was "much smaller than a big solar flare."
Still, scientists were surprised that a magnetar so far away could alter the ionosphere.
"That it can reach out and tap us on the shoulder like this, reminds us that we really are linked to the cosmos," said Phil Wilkinson of IPS Australia, that country's space weather service.
"This is a once-in-a-lifetime event," said Rob Fender of Southampton University in the UK. "We have observed an object only 20 kilometers across [12 miles], on the other side of our galaxy, releasing more energy in a tenth of a second than the Sun emits in 100,000 years."
Some researchers have speculated that one or more known mass extinctions hundreds of millions of years ago might have been the result of a similar blast altering Earth's atmosphere. There is no firm data to support the idea, however. But astronomers say the Sun might have been closer to other stars in the past.
A similar blast within 10 light-years of Earth "would destroy the ozone layer," according to a CfA statement, "causing abrupt climate change and mass extinctions due to increased radiation."
The all-clear has been sounded, however.
"None of the known sample [of magnetars] are closer than about 4,000-5,000 light years from us," Gaensler said. "This is a very safe distance."
Cause a mystery
Researchers don't know exactly why the burst was so incredible. The star, named SGR 1806-20, spins once on its axis every 7.5 seconds, and it is surrounded by a magnetic field more powerful than any other object in the universe.
"We may be seeing a massive release of magnetic energy during a 'starquake' on the surface of the object," said Maura McLaughlin of the University of Manchester in the UK.
Another possibility is that the magnetic field more or less snapped in a process scientists call magnetic reconnection.
Gamma rays are the highest form of radiation on the electromagnetic spectrum, which includes X-rays, visible light and radio waves too.
The eruption was also recorded by the National Science Foundation (news - web sites)'s Very Large Array of radio telescopes, along with other European satellites and telescopes in Australia.
Explosive details
A neutron star is the remnant of a star that was once several times more massive than the Sun. When their nuclear fuel is depleted, they explode as a supernova. The remaining dense core is slightly more massive than the Sun but has a diameter typically no more than 12 miles (20 kilometers).
Millions of neutron stars fill the Milky Way galaxy. A dozen or so are ultra-magnetic neutron stars -- magnetars. The magnetic field around one is about 1,000 trillion gauss, strong enough to strip information from a credit card at a distance halfway to the Moon, scientists say.
Of the known magnetars, four are called soft gamma repeaters, or SGRs, because they flare up randomly and release gamma rays. The flare on SGR 1806-20 unleashed about 10,000 trillion trillion trillion watts of energy.
"The next biggest flare ever seen from any soft gamma repeater was peanuts compared to this incredible Dec. 27 event," said Gaensler of the CfA.
Is it possible the energy is in a narrow beam instead of omni directional. That would mean less energy/perhaps lots less energy? Neil
I know! Wasn't that awesome??? Have any of you yet looked into the Einstein @ Home project and/or thought about trying to hook into that?
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