'Black widow' pulsars kill and devour spinning neutron stars
Just like black widow spiders and their Australian cousins, known as redbacks, kill and devour their male partners, astronomers have noted similar behavior among two rare breeds of binary system that contain rapidly spinning neutron stars, also known as pulsars.
"The essential features of black widow and redback binaries are that they place a normal but very low-mass star in close proximity to a millisecond pulsar, which has disastrous consequences for the star," Roger Romani, a member of the Kavli Institute for Particle Astrophysics and Cosmology, an institute run jointly by Stanford and SLAC National Accelerator Laboratory in Menlo Park, California, said.
Black widow systems contain stars that are both physically smaller and of much lower mass than those found in redbacks.
So far, astronomers have found at least 18 black widows and nine redbacks within the Milky Way, and additional members of each class have been discovered within the dense globular star clusters that orbit our galaxy.
One black widow system, named PSR J1311-3430 and discovered in 2012, sets the record for the tightest orbit of its class and contains one of the heaviest neutron stars known. The pulsar's featherweight companion, which is only a dozen or so times the mass of Jupiter and just 60 percent of its size, completes an orbit every 93 minutes -- less time than it takes to watch most movies.
Initial estimates put the neutron star at about 2.7 solar masses, but more recent studies allow a range of values extending down to 2 solar masses, still among the highest-known for neutron stars.
When a massive star explodes as a supernova, the crushed core it leaves behind -- a neutron star -- squeezes more mass than the Sun into a ball no larger than Washington, DC.
When young, an isolated neutron star rotates tens of times each second -- or a few thousand revolutions per minute -- and generates beams of radio, visible light, X-rays and gamma rays that astronomers observe as pulsed emission whenever the beams sweep past Earth. They also generate powerful outflows, or "winds," of high-energy particles.
The power for all this derives from the neutron star's rapidly spinning magnetic field, and over time, as solitary pulsars wind down, their emissions fade.
(Posted on 21-02-2014)
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