23Aug2012

Star Consumes a Planet.

An artist's impression of a red supergiant engulfing a Jupiter-like planet as it expands. Credit: NASA

So far we’ve discovered a huge amount of planets orbiting a variety of stars, but this is the first time astronomers have uncovered evidence of a star devouring one of its offspring. When a planet comes up “missing”, it’s time to take a closer look at its parent star – in this case, a red giant older than the Sun and about eleven times bigger.

“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,” said Alexander Wolszczan, Evan Pugh Professor of Astronomy and Astrophysics at Penn State University, who is one of the members of the research team. Wolszczan also is the discoverer of the first planet ever found outside our solar system.

However, that’s not all that’s been discovered in this odd solar system. The same red giant star, named BD+48 740, appears to have a massive planet contained in a highly elliptical orbit. 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, were hard at work utilizing the Hobby-Eberly Telescope in search of its solar system when they uncovered evidence of planetary destruction. Just what was the clue? Try an unusual chemical composition of the host star and the strange elliptical orbit of a surviving planet.

The first evidence of a planet's destruction by its aging star indicates that the missing planet was devoured as the star began expanding into a "red giant" — the stellar equivalent of advanced age. "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," said Alexander Wolszczan, Evan Pugh Professor of Astronomy and Astrophysics at Penn State and the discoverer of the first planet ever found outside our solar system. Credit: Marty Harris/McDonald Obs./UT-Austin

“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.”

As for the remaining planet, it’s pretty incredible. This newly discovered member is 1.6 times as massive a 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.

“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.”

Bon apetit!

Original Story Source: Penn State News Release.