Cannibal star discovered

An astronomer says he’s caught a star in the act of chewing up a companion and spitting out a second generation of exoplanets.

Using data from NASA’s Chandra X-ray Observatory, Joel Kastner, professor at Rochester Institute of Technology, has found evidence that a variable star in the constellation of Pisces, BP Piscium, could be a one billion-year-old red giant that has gobbled up a star or planet in its vicinity.

The star’s been puzzling astronomers for 15 years, as it shows characteristics of both age and youth.

But Kastner says its youthful appearance is caused by an orbiting disk like those that form planets around young stars, and prominent jets extending from the poles that eject material at high velocity.

But this was contradicted by the fact that the star is isolated, whereas most young stars form in clusters.

The star also lacks the abundance of lithium on its surface that is typical of young stars. And other key spectral features involving the star’s radius and surface gravity also point to the star’s advanced age.

“The last piece of evidence, which, to me, is the nail in the coffin that BP Psc is old rather than young, is that its rate of X-ray production is very similar to old, yet rapidly spinning, giant stars that have surface temperatures similar to BP Psc,” Kastner says.

The rate of X-rays coming from the star are in keeping with a class of rapidly rotating old stars that are thought to be the result of one star swallowing another.

“These giant stars’ companions have fallen inside and spun them up. But we’ve never actually caught one in the act,” says Kastner.

“Our working speculation is that we are observing the star right at the point at which it has swallowed its companion and hence formed a disk. Some of the material that used to be its companion has fallen onto the star and some has been shot out at high speeds, and that’s what we’re seeing.”

Kastner says the discovery could help astronomers looking for exoplanets by giving them a new place to search.