Skip to comments.Starburst Was One of Brightest Objects Observed on Earth
Posted on 02/18/2005 9:31:11 PM PST by neverdem
For a fraction of a second in December, a dying remnant of an exploded star let out a burst of light that outshone the Milky Way's other half-trillion stars combined, astronomers announced today.
Even on Earth, half a galaxy away, the starburst was one of the brightest objects ever observed in the sky, after the Sun and perhaps a few comets. The magnitude of the event caught most astronomers by surprise.
"Whoppingly bright," said Dr. Brian Gaensler, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "It gave off more energy in 0.2 seconds than the Sun does in 100,000 to 200,000 years."
No one on Earth directly saw the flare, because most of the light was gamma rays, photons that are more energetic than X-rays and are blocked by the atmosphere. But the Dec. 27 pulse registered on instruments aboard 15 spacecraft, including NASA's new Swift satellite, which was designed to record cosmic gamma rays and had been turned on just the week before.
Dr. Neil Gehrels, the lead scientist for Swift, said flares of that magnitude could be expected just once in a millennium. "That seems so improbable it's a puzzle right now," he said. "There's something going on here that we don't understand."
The radiation also pushed in the Earth's ionosphere, an envelope of charged gas at the top of the atmosphere, and distorted long-wavelength radio signals.
"It was really the big one," said Dr. Kevin Hurley, a researcher at the Space Sciences Laboratory at the University of California, Berkeley. "You could not have missed it."
Astronomers pinpointed the origin of the pulse as a neutron star known as SGR 1806-20, about 50,000 light-years distant in the constellation Sagittarius. Neutron stars are remnants of stars after they have exploded in supernovas, and SGR 1806-20 is one of about 10 unusual neutron stars known as magnetars, which have extraordinarily strong magnetic fields, a quadrillion times as strong as Earth's.
Sudden shifts in the intense magnetic fields are believed to generate flares, in much the way the Sun generates solar flares, and two giant magnetar flares had been observed previously, one in 1979 and one in 1998. The Dec. 27 flare, however, was 100 times as powerful.
One physicist, Dr. David Eichler of Ben-Gurion University in Israel, wrote a paper in 2002 suggesting that magnetars might be capable of such cataclysmic explosions, but for most scientists, Dr. Gaensler said, "we had no idea they could make a flare this big." SGR 1806-20 has as much mass as 1.5 Suns, compressed into an incredibly dense ball about a dozen miles wide, and it spins around once every 7.5 seconds, which is slow for a neutron star. Discovered in 1979, SGR 1806-20 has at times been noisy, firing off small gamma ray flares, and at other times quiet. Its activity picked in the past year.
"In retrospect, I guess you could say it was getting ready to let go," Dr. Hurley said, adding that the magnetic fields, held in place by the crust of the star, had become twisted, building stress. "At some point, it gives way like an earthquake," he said.
Astronomers presented their observations at a NASA news conference today, and two scientific papers describing the event will be published in an upcoming issue of the journal Nature.
In the aftermath of the flare, Dr. Gaensler, lead author of one of the Nature papers, and his colleagues used radio telescopes on Earth to track a shock wave radiating outward from the star. They were surprised to find the bubble expanding at a third of the speed of light. "Which is not what you tend to see in the galaxy every day," he said.
SGR 1806-20 itself continues to spin as before, one revolution every 7.5 seconds.
"Amazingly, the neutron star is still there," Dr. Gaensler said. "It did not explode or blow itself apart to bits."
The magnetar flare might help solve a cosmic mystery of gamma ray bursts, the prime mission of the Swift satellite. Bursts lasting for minutes are believed to be caused by the collisions of black holes - events that are even more violent than magnetar flares, which occur much farther away - but astronomers had been at a loss to explain shorter bursts lasting a couple of seconds or less.
Now they have at least a partial answer: some of the bursts are magnetar flares originating from other galaxies.
"It is clear magnetar flares make short gamma ray bursts," said Dr. Robert C. Duncan of the University of Texas. "It is at least a significant fraction of them."
However, that still may not be whole answer. Dr. Gehrels said that when astronomers looked in the direction of three recent short gamma ray bursts, those parts of the sky turned out empty.
"It just all fits so well and then there were no galaxies there," Dr. Gehrels said. But he said that as Swift observes more gamma ray bursts, "We should know in the next couple of months the answer to this."
FReepmail me if you want on or off my health and science ping list.
as usual, I missed it.
dead star went boom.
You didn't miss it- you got bathed in gamma rays just like everybody else ;-)
I seem to recall microsecond and faster rotation times for neutron stars. Could be my addled brain playing tricks on me again.
It's not easy being green...
oh, I dunno bout that... (see your email)
DD - ping to 12
EATB, ya might be so kind as to add Dawsonville_Doc to your astrophysics pinglist?
Starburst Was One of Brightest Objects Observed on Earth? For a minute, I thought it said Starbucks Was One of Brightest Objects Observed on Earth. That's a relief!
The barristas I've met at Starbucks usually aren't that bright (but they think they are with their Theater History degrees) and generally have multiple face piercings and green hair.
OK, back to the topic at hand...
~ Blue Jays ~
It is at the bottom of the table follwing the Section titled: March 5th Burst Theories.
Thanks for the links.
I really have not been keeping a ping list on this topic, I think Neverdem is though, although it might be broader than what some would like.
I built the ping list above from those that had commented on the thread I put up a link to.