Stars Swallow Planets and Researchers Have Proof

Harald Franzen Scientific American

Some stars swallow their own planets, according to a team of Spanish and Swiss researchers. Using a highly sensitive spectrograph, they found incriminating evidence for such cannibalism in the light emitted by HD82943, a dwarf star in the constellation Hydra. Their findings are published in today's issue of Nature.

A light spectrum analysis of HD82943—a star slightly hotter and larger than the sun, harboring its own planetary system—revealed that it contained traces of an isotope of lithium called Lithium-6, or 6Li. Although 6Li is common in planets, it burns up quickly in stars after they are born and thus shouldn't exist in a star like HD82943. "The simplest and most convincing way to explain this observation is that one or more planets, or at least planetary material, have fallen into the star, sometime after it passed through its early evolutionary stage," Nuno Sandos of the Geneva Observatory says. The fact that the star still has 6Li left to burn suggests that it engulfed one of its planets sometime within the past 30 million years.

"We don't know of any other mechanism to explain the presence of 6Li," agrees Garik Israelian of the Astrophysics Institute of the Canary Islands. To confirm their theory, the scientists looked at another star that shared HD82943's characteristics except that it did not have planets. In keeping, they found that did not have 6Li in its spectrum. The researchers hope that this finding will help to explain how so-called exoplanets form and if this kind of cannibalism is a common process.