The first evidence of a star gobbling up a planet has been found by a team of international astronomers.
The unlucky planet was devoured by a star called BD+48 740, which lies about 1,800 light years away and had expanded in its old age into a “red giant”.
This cosmic dining scene is something that will play out in our own solar system.
Team leader Alex Wolszczan, from Penn State University, said: “A similar fate may await the inner planets in our solar system, when the Sun becomes a red giant and expands all the way out to Earth's orbit some five-billion years from now.”
The star expanded into a red giant and destroyed a nearby planet, say astronomers (illustration)
The sun will remain a red giant for billions of years, before compressing into a “white dwarf”, about the size of the Earth, for a few billion years more while it cools down.
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 in Texas to study the aging star and to search for planets around it.
The evidence includes the star's peculiar chemical composition, which was a trifle “planety”, plus the highly unusual elliptical orbit of its surviving planet.
The Hobby-Eberly Telescope, which astronomers used to make the remarkable discovery
"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."
The second piece of evidence discovered by the astronomers is the highly elliptical orbit of the star's newly discovered massive planet, which is at least 1.6 times as massive as Jupiter.
"We discovered that this planet revolves around the star in an orbit that is only slightly wider than that of Mars at its narrowest point, but is much more extended at its farthest point," Niedzielski said. "Such orbits are uncommon in planetary systems around evolved stars and, in fact, the BD+48 740 planet's orbit is the most elliptical one detected so far."
Because gravitational interactions between planets are responsible for such peculiar orbits, the astronomers suspect that the dive of the missing planet toward the star before it became a giant could have given the surviving massive planet a burst of energy, throwing it into an eccentric orbit like a boomerang.
The paper describing this discovery is posted in an early online edition of the Astrophysical Journal Letters.