A Rare Event of Planet Destruction by Its Star

For the first time the scientists have found evidence of red giant star that is devouring its own planet.

"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 Alex Wolszczan, an Evan Pugh Professor of Astronomy and Astrophysics at Penn State, University, who is one of the members of the research team. He is noted for being the first discoverer of the planet that is located outside our solar system.

In the elliptical orbit that surrounds the red giant star 'BD+48 740' the astronomers noticed a massive planet which is eleven times bigger than the sun.

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," explained Eva Villaver of the Universidad Autonoma de Madrid in Spain. "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."

The evidence of the missing planet was tracked by the team that included, Monika Adamow, Gregorz Nowak and Andrzej Niedzielski of Nicolaus Copernicus University in Torun, Poland. 

Hobbey Eberly Telescope was used by the team to gain in-depth information on the aging star and also to hunt for the existence of some planets around it.

According to the Penn State release, the evidence consists of the star's peculiar chemical composition, and the extremely odd elliptical orbit of its one existing 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.

The researchers were surprised by the presence of lithium as it is one such element that is easily damaged in stars. And what is usual is its presence in high concentration in the older star.

"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."

Apart from this what caught the attention of the researchers is the elliptical orbit 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." 

The researcher's feel the gravitational force that exists between two planets are the main cause for the existence of such unique orbits. They also suspect that the energy released when another planet smashes into the star, it triggers the large planet to form orbits.

The findings are carried out in an early online edition of the Astrophysics Journal Letters.