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Tuesday, 14 September 2010 20:15

Star Finds Fountain of Youth by Eating Companion

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A sun-like star has kept up a youthful appearance by devouring its smaller neighbors. A new X-ray image of the star BP Piscium reveals the shredded corpse of a companion star or giant planet that the star recently

consumed.

“It appears that BP Psc represents a star-eat-star Universe, or maybe a star-eat-planet one,” said astronomer Joel Kastner of the Rochester Institute of Technology in a press release.

BP Psc has been an enigma since Kastner and astronomer Ben Zuckerman of the University of California, Los Angeles, first looked at it 15 years ago. Optical images from the Lick Observatory showed that the star, which lies about 1,000 light-years from Earth, has a pair of long jets several light-years long shooting away from its poles. BP Psc is also surrounded by a dusty, gaseous disk. Both these features are characteristic of young stars.

But BP Psc is also a loner, while most young stars live in clusters. Other details, like the star’s radius, surface gravity and composition, point to a much older star.

New observations from NASA’s Chandra X-Ray Observatory clinch the debate. If BP Psc were as young as it seems, it would be spewing X-rays in the hundreds or thousands per day. Instead, the star emits few X-rays at a time.

“We stared at BP Psc for one day with Chandra and only detected about 18 X-rays,” Kastner said. “We could almost name them.”

This X-ray production rate is similar to another class of old, rapidly rotating stars with temperatures close to BP Psc’s.

“These giant stars’ companions have fallen inside and spun them up,” Kastner said. “But we’ve never actually caught one in the act. I think BP Psc is an example of such an interaction.”

In a paper in Astrophysical Journal Letters, Kastner and colleagues propose that BP Psc is a billion years old and just entering its red giant phase, in which aging stars run out of fuel and swell to engulf any planets or binary stars that are unfortunate enough to be nearby. Our sun may eventually swallow the Earth as it becomes a red giant in a few billion years.

“BP Psc shows us that stars like our sun may live quietly for billions of years,” said coauthor David Rodriguez from UCLA in a press release. “But when they go, they just might take a star or planet or two with them.”

Despite all this destruction, a second round of planets may rise from the dust. Observations from the Spitzer Space Telescope show possible evidence for a giant planet in the disk surrounding BP Psc.

Cosmic cannibals crop up in every corner of the universe. Here at Wired Science, we’ve seen galaxies ripping apart and devouring their smaller galactic neighbors, and pulsars whose speedy spinning is fueled by dead companions.

“It just shows it’s not always friendly out there,” Kastner said.

Image: The left panel is a composite X-ray and optical image of BP Psc, and the right panel is an artists illustration of what the region around this stellar cannibal may look like. X-ray: NASA/CXC/RIT/J.Kastner et al, Optical: UCO/Lick/STScI/M.Perrin et al; Illustration: NASA/CXC/M.Weiss

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Authors: Lisa Grossman

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