Astronomy and astrophysics

Puzzling binary star system detected

White dwarf avoids cannibalizing its close companion.

Astronomers have discovered a puzzling star system in which two bodies orbit each other extremely tightly, without one feeding off the other.

Saul Rappaport at the Massachusetts Institute of Technology in Cambridge and his colleagues, and a separate team led by Steven Parsons at the University of Sheffield, UK, independently discovered the binary system, called WD1202-024, in data from NASA’s Kepler telescope. The researchers noticed that a white dwarf, the remains of a once Sun-like star, was being totally eclipsed every 71.2 minutes. This suggests it is in orbit with a brown dwarf, an object too light to form a normal star.

Rappaport’s team investigated how these bodies could come to orbit each other at less than the distance between Earth and the Moon without the more massive star draining matter from its companion. Their models suggest that the white dwarf’s predecessor probably expanded into a red giant, engulfing the brown dwarf. This caused the less-massive body to spiral inwards, throwing out most of the matter from the giant and leaving it as a white dwarf.

The authors predict that the white dwarf will creep close enough to start feeding off its companion in less than 300 million years.