A dead, spinning star has been found feeding on its stellar companion, whittling it down to an object smaller than some planets.
"This object is merely the skeleton of a star," says study team member Craig Markwardt of NASA's Goddard Space Flight Center in Maryland. "The pulsar has eaten away the star's outer envelope, and all that remains is its helium-rich core."
Pulsars are the cores of burnt out "neutron" stars that spin hundreds of times per second, faster than a kitchen blender.
The system was discovered in early June when NASA's Swift and Rossi X-ray Timing Explorer (RXTE) satellites picked up an outburst of X-rays and gamma rays in the direction of the Milky Way galactic center in the constellation Sagittarius.
"It's essentially a white dwarf that has been whittled down to a planetary mass," said study team member Christopher Deloye of Northwestern University.
This caused the two stars to draw closer together, while simultaneously ejecting the red giant's envelope into space.
After billions of years, little remains of the companion star, and it's uncertain whether it will survive. "It's been taking a beating, but that's part of nature," said study team member Hans Krimm, also of NASA Goddard.
Today, the two objects are so close to each other that the neutron star's powerful gravity siphons gas from its companion to form a spinning disk around itself. The disk occasionally dumps large quantities of gas onto the neutron star, creating an outburst like the one detected in June.
The system will be detailed in two studies authored by Krimm's team and a team led by Deepto Chakrabarty of MIT, which reached the same conclusions, to be published in an upcoming issue of Astrophysical Journal Letters.
"Given that we don't know the exact mass of either companion, ours could be the smallest," Krimm said.
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