AAS Meeting - millisecond pulsars
Published on Jan 10, 2007 at 1:11 pm.
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Filed under conference blogging, neutron stars.
Well, we are still meeting here in Seattle. It just goes on. But, this is good. I would MUCH rather be doing this than I would be back home going to faculty meetings that I hate and getting ready for the semester. Actually, I’m already ready to go.
Today, we had some talks on millisecond pulsars. For those that don’t know, millisecond pulsars are extremely rapidly rotating neutron stars. When a massive star dies, the core collapses into a neutron star. The rest of the star explodes in a supernova explosion. The core collapsing speeds up its rotation. This is much the same as when a figure skater is spinning and pulls her arms in tight to her body, she speeds up how fast she is spinning. When a massive star collapses, the resulting neutron star should be spinning perhaps a hundred times per second, or a bit slower. As time passes, the neutron star slows its rotation through a variety of processes. A typical neutron star rotates about once ever few tenths of a second up to once every couple of seconds. As the neutron star rotates, if it has a hot spot, then this hot spot beams radiation out into space, and the rotation of the neutron star causes that beam to sweep through space like a search light. If you are in the line of that beam, you see a flash with a very regular period. These were first discovered with radio waves by Jocelyn Bell, and we call them pulsars. So, pulsars are the observation of rotation neutron stars.
In the early 1980’s, a new class of pulsar was found, one which pulsed once every few milliseconds, not once per second! At first, you might think that these would be exceedingly young neutron stars, from what I said before. Well, actually, they are quite old systems. We don’t think that neutron stars can rotate that quickly when they form, so something had to speed them up. The model quickly developed was that they were part of a binary system in which they accrete gasses from their companion. As these gasses fall inward, the rotating gasses cause the neutron star to speed up to conserve angular momentum. During the accreting process, the gasses make an unusually hot spot creating short period X-ray pulses. Astronomers used the Rossi X-Ray Timing Explorer satellite to search for these X-ray pulsars, and finally found them after many years of searching. The talks today were associated with the Rossi Prize awarded to Deepto Chakrabarty, Tod Strohmayer, and Rudy Wijnands for their work in this area. The talks were about the properties of these X-ray millisecond pulsars.
-Astroprof
