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27 Dec 2009
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Oddity for Today
27 Dec 2009 11:56 amThis is the fifth anniversary of the brightest SGR 1806-20 flare; for a fifth of a second, this neutron star was brighter than the full moon, despite being roughly 50,000 light years away. Most of the galactic core and several thick interstellar dust lanes normally obscure SGR 1806-20. To give a bit more perspective, for that brief period SGR 1806-20 was more than one hundred times brighter than a supernova. Unlike a supernova, this was also a repeatable event; SGR 1806-20 has been seen to flare before, though not so brightly.
SGR 1806-20 is a particular type of neutron star having an extremely powerful magnetic field; this type is generally referred to as a magnetar. SGR 1806-20's magnetic field is roughly 100,000,000,000 times as strong as the strongest MRI machine (yes, I just had to write that out).
The "SGR" identifier stands for Soft Gamma Repeater, an object showing repeated short flashes of soft gamma rays. The phenomenon was first recognized as being distinct from the more common gamma ray bursts around 1987, and it's now thought that SGRs are magnetars (as opposed to X-ray binary stars or quark stars or other oddness). SGRs also seem to be rotating much slower than most neutron stars -- a few seconds, instead of many times a second. They also seem to be quite young (less than ten thousand years old, though of course much more time has passed for the flares to reach us). Not all magnetars are SGRs, either -- anomalous X-ray pulsars (AXPs) are also thought to be magnetars.
At this time, there are five known SGRs and nine known AXPs, with a few more promising candidates. It's also thought that there are a very large number of "dead" magnetars out there waiting to be found, still highly magnetized but very slowly spinning, dimly giving off x-rays.
SGR 1806-20 is a particular type of neutron star having an extremely powerful magnetic field; this type is generally referred to as a magnetar. SGR 1806-20's magnetic field is roughly 100,000,000,000 times as strong as the strongest MRI machine (yes, I just had to write that out).
The "SGR" identifier stands for Soft Gamma Repeater, an object showing repeated short flashes of soft gamma rays. The phenomenon was first recognized as being distinct from the more common gamma ray bursts around 1987, and it's now thought that SGRs are magnetars (as opposed to X-ray binary stars or quark stars or other oddness). SGRs also seem to be rotating much slower than most neutron stars -- a few seconds, instead of many times a second. They also seem to be quite young (less than ten thousand years old, though of course much more time has passed for the flares to reach us). Not all magnetars are SGRs, either -- anomalous X-ray pulsars (AXPs) are also thought to be magnetars.
At this time, there are five known SGRs and nine known AXPs, with a few more promising candidates. It's also thought that there are a very large number of "dead" magnetars out there waiting to be found, still highly magnetized but very slowly spinning, dimly giving off x-rays.
