A Planet's Destruction by its Star
The astronomers also discovered a massive planet in a surprisingly elliptical orbit around the same red-giant star, named BD+48 740, which is older than the Sun with a radius about eleven times bigger. Wolszczan and the team’s other members, Monika Adamow, Grzegorz Nowak, and Andrzej Niedzielski of Nicolaus Copernicus University in Torun, Poland; and Eva Villaver of the Universidad Autonoma de Madrid in Spain, detected evidence of the missing planet’s destruction while they were using the Hobby-Eberly Telescope to study the aging star and to search for planets around it. The evidence includes the star’s peculiar chemical composition, plus the highly unusual elliptical orbit of its surviving planet.
“Our detailed spectroscopic analysis reveals that this red-giant star, BD+48 740, contains an abnormally high amount of lithium, a rare element created primarily during the Big Bang 14 billion years ago,” Adamow said. Lithium is easily destroyed in stars, which is why its abnormally high abundance in this older star is so unusual. “Theorists have identified only a few, very specific circumstances, other than the Big Bang, under which lithium can be created in stars,” Wolszczan added. “In the case of BD+48 740, it is probable that the lithium production was triggered by a mass the size of a planet that spiraled into the star and heated it up while the star was digesting it.”
“Catching a planet in the act of being devoured by a star is an almost improbable feat to accomplish because of the comparative swiftness of the process, but the occurrence of such a collision can be deduced from the way it affects the stellar chemistry,” Villaver explained. “The highly elongated orbit of the massive planet we discovered around this lithium-polluted red-giant star is exactly the kind of evidence that would point to the star’s recent destruction of its now-missing planet.”