When the nuclear fusion that powers stars flickers out, most collapse and explode in a dramatic supernova. Now, astronomers have discovered a quieter fate for two pairs of stars. One in each couple was snuffed out after their vampire-like partner apparently drained off most of their mass.
Stars condense out of tenuous clouds of gas. The protostellar cloud collapses around a dense core made mostly of hydrogen, heating it until the hydrogen nuclei begin to fuse and heat up the star. Often, a single cloud gives birth to several stars simultaneously and the newborns pair off in a gravitational orbital dance.
The nearby companion can dramatically alter the fate of a smaller star. If the partners drift close enough, the gravitational pull of the more massive star will drag material off its neighbor. If they get too close, some theorists speculated, the larger star could skim off enough mass that nuclear fusion shuts down--snuffing the donor out like a candle. But because these extinguished stars have no internal power source, they don't shine brightly. Years of searching had failed to turn up a single example.
But last fall, astronomers got lucky. The temporary dimming when matter stopped flowing between the stars in two binary systems--LL Andromedae and EF Eridani--gave their whittled down companions a brief chance to shine, reports a team led by astronomer Steve Howell of the Planetary Science Institute in Tucson, Arizona, in March in Astrophysical Journal Letters. The team glimpsed the faint glow of methane from LL Andromedae and steam from EF Eridani using the 3.8-meter United Kingdom Infrared Telescope (UKIRT) on Mauna Kea, Hawaii. The emissions indicated that the two stars are a chilly 1300° and 1650°C, respectively. "That is about what we predicted from our best guess about what these stars would look like," Howell says.
"These are weird objects," says Shrivanas Kulkarni, an astrophysicist at the California Institute of Technology in Pasadena. Kulkarni thinks that investigating these shuttered stars will reveal more about exoplanets, which are also bathed in the light of a companion star.