Giant eruption reveals 'dead' star
June 16, 2009An enormous eruption has found its way to Earth after travelling for many thousands of years across space. Studying this blast with ESA's XMM-Newton and Integral space observatories, astronomers have discovered a dead star belonging to a rare group: the magnetars.
X-Rays from the giant outburst arrived on Earth on 22 August 2008, and triggered an automatic sensor on the NASA-led, international Swift satellite. Just twelve hours later, XMM-Newton zeroed in and began to collect the radiation, allowing the most detailed spectral study of the decay of a magnetar outburst.
The outburst lasted for more than four months, during which time hundreds of smaller bursts were measured. Nanda Rea from the University of Amsterdam led the team that performed the research. "Magnetars allow us to study extreme matter conditions that cannot be reproduced on Earth," she says.
Magnetars are the most intensely magnetised objects in the Universe. Their magnetic fields are some 10 000 million times stronger than Earth's. If a magnetar were to magically appear at half the Moon's distance from Earth, its magnetic field would wipe the details off every credit card on Earth.
This particular magnetar, known as SGR 0501+4516, is estimated to lie about 15 000 light-years away, and was undiscovered until its outburst gave it away. An outburst takes place when the unstable configuration of the magnetic field pulls the magnetar's crust, allowing matter to spew outwards in an exotic volcanic eruption. This matter tangles with the magnetic field which itself can change its configuration, releasing more energy. And this was where Integral came in.
Only five days after the big eruption, Integral detected highly energetic X-rays coming from the outburst, beyond the energy range that XMM-Newton can see. It is the first time such transient X-ray emission has been detected during the outburst. It disappeared within 10 days and was probably generated as the magnetic configuration changed.
Magnetar outbursts can supply as much energy to Earth as solar flares, despite the fact they are far across our Galaxy, whereas the Sun is at our celestial doorstep. There are two ideas as to how a magnetar forms. One is that it is the tiny core left behind after a highly magnetic star has died. But such magnetic stars are very rare, with just a few known in our Galaxy.
Another suggestion is that during the death of a normal star, its tiny core is accelerated, providing a dynamo that strengthens its magnetic field, turning it into a magnetar.
Currently most astronomers favour the first idea but as yet they have no conclusive proof. "If we could just find a magnetar in a cluster of highly magnetic stars, that would prove it," says Rea.
So far only 15 magnetars in total are known in our Galaxy. SGR 0501+4516 is the first new soft gamma repeater, one of the two types of magnetars, discovered after a decade of searches. So, astronomers continue to search for more, waiting for the next giant eruption. As for their newly discovered SGR 0501+4516, the team has been granted time to return and observe it again next year with XMM-Newton. Now they know where to look, they hope to detect the object in a quiescent state, rather than in outburst, so that they can study the calm after a big storm.
Source: European Space Agency (news : web)
Jan 13, 2009 |
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Like that would be the worst thing that could happen if something more massive than the Sun was dumped on our doorstep.
'The horror, I can't buy anything in the ten seconds of life remaining.'
Ethelred
If the magnetic fields of magnetars "are some 10 000 million times stronger than Earth's", how do they compare with the magnetic fields of neutron stars?
With kind regards,
Oliver K. Manuel
http://www.omatumr.com
http://en.wikiped...Magnetar
Ethelred
. . . study rest masses of the 3,000 atoms that comprise the entire visible universe and discover for yourself why neutrons are so energized in large assemblages of neutrons [Or read: "Attraction and repulsion of nucleons: Sources of stellar energy", Journal of Fusion Energy 19 (2001) 93-98].
With kind regards,
Oliver k. Manuel
http://www.omatumr.com/
Thanks, Ethelred.
What is the magnetic field of a typical neutron star?
~1,000,000,000,000 Gauss?
How much greater is the magnetic field of a magnetar?
Thanks,
Oliver K. Manuel
Not a clue. I think it would depend on the rotation rate and that it might depend on the magnetic field of the star before the supernova. I don't think there is a way to experimentally determine a star's magnetic field except by inference based on what goes on if there is an accretion disc.
Let me see if there is an answer of some sort.
http://www.astro....tar.html
That one does have it in that range. Says it is inferred.
Ethelred
QubitTroll will be released from my sig at the end of June.
Thanks, Ethelred, that's helpful.
If an ordinary star, like the Sun, had a neutron star at its core, what would be the range of magnetic fields expected at its surface?
With kind regards,
Oliver K. Manuel
Assume for a moment that neutron star could be smaller. Say .8 Solar mass. The hydrogen AND the helium on the surface would be at a sufficient pressure and temperature to fuse. Right there on the surface. Kicking out raw x-rays. The whole solar system would be sterilized.
Ignore that for the moment. The magnetic field would restrict movement of ionized gases. If the field had a different poles than the mass itself did I suppose that would might churn the gas. Assuming there would be any gas. This is the thing about the surface. The star wouldn't have a radius of around 450,000 miles as the Sun does. The surface of a neutron star is believed to consist of degenerate matter. I don't see how it could be anything else.
Pretend that it could be the same radius as our sun. Then it might have a similar magnetic field at the surface. Its the compression of the field that causes the high field strength in a neutron star. Of course there is the idea that there is superconduction going on and that could increase the field strength beyond the level of the original star. So I don't know. I suppose it could be similar to what we see or much higher.
Ethelred
QubitTroll will be released from my sig at the end of June.