Friday, October 24, 2014
Astronomers have accidentally discovered the brightest pulsar on record!!
NuSTAR is a space telescope NASA designed specifically to study black holes. But it found something much, much brighter. Astronomers at NASA say it is the most luminous pulsar ever discovered...
What's a pulsar? After a star goes nova, pretty much only the core is left. Some cores are massive enough to collapse inward from the effects of gravity, and form a black hole. Some stars don't have enough left, and collapse just a little to become a dense white dwarf -- a star in which no fusion is occurring, but which emits light due to its high heat (eventually turning red, and then black). But some stars are in-between, too big to stop at becoming a white dwarf, and yet not big enough to collapse into a black hole.
These stars are neutron stars. The atoms in a neutron star are stripped of everything but neutrons, hence the name. The surface of the star is iron, but below that it's pure neutrons. Because a star about the size of our Sun is packed into a space just 6 miles across, neutron stars are very dense and rotate very fast. (It's like a figure skater pulling in their arms as they rotate; they speed up, although all that's changed is the density.)
As the neutron star rotates, it emits an intense beam of radiation out of its magnetic poles. The magnetic poles are not the same as the axis on which the star rotates, so the beam carves a kind of circle north and south of the neutron star. If the neutron star rotates fast enough, this beam of radiation can be STUPENDOUSLY powerful.... creating a pulsar. On Earth, we can only see this beam if it points directly at us. And since the neutron star is rotating, that beam will sometimes point at us and sometimes not -- e.g., it will seem to flicker on and off. Hence the "pulsing" of a pulsar.
Some neutron stars are locked in orbit with a normal star. Being so dense, they pull gas off the companion star. The gas is channeled by the magnetic field of the neutron star so that the gas lands only on the magnetic poles. That gas can reach nearly half the speed of light, and as it impacts the surface of the neutron star it gives off huge amounts of X-rays. These pulsars are thus known as X-ray pulsars or accretion-powered pulsars.
Some neutron stars rotate only very slowly. But such neutron stars have very, very powerful magnetic fields. They become known as magnetars, because electromagnetic energy shoots out of their magnetic poles so powerfully.
This new pulsar is a mega-powerful X-ray pulsar. Astronomers at first mistook it for a black hole. They then realized there wasn't a black hole there, but a neutron star. After measuring the neutron star's output, they found it was putting out as much energy as 10 million suns -- shockingly powerful for a pulstar. Astronomers aren't sure why the pulsar is so bright, but will continue to study it in hope of learning more. The discovery really shakes up what theorists know about black holes and ultraluminous X-rays.