An unusual star may have swallowed its stellar companion and burped out a planet-forming cloud as a result, a new study reports.
The star, called BP Piscium, is surrounded by a thick disc of gas and dust from which it appears to be sucking up new material at a prodigious rate.
These properties are typical of young stars, but BP Piscium appears to be much older, based on the weak signs of lithium in its light spectrum. Younger stars have plenty of lithium, but it gets destroyed as stars age.
A team of scientists led by Carl Melis of the University of California in Los Angeles (UCLA), US, reported the unusual star at a meeting of the American Astronomical Society in Austin, Texas, US, in January.
Now Benjamin Zuckerman, also of UCLA, together with Melis and others have released a more detailed study of the star online.
The researchers believe the star is middle aged, having exhausted the hydrogen fuel at its core and swelled to become a giant.
BP Piscium's distance has not been measured directly, but the observations fit a star that weighs about 1.8 times the mass of the Sun and lies about 1000 light years away. Based on this distance, they calculate that the star's dusty disc contains the mass of roughly 50 Earths.
To explain the presence of the dusty disc, the astronomers suggest that when the star grew to become a red giant, its atmosphere engulfed a smaller companion star. The companion, orbiting inside the atmosphere of the primary star, would stir up the gas there, throwing it out to make a disc.
The disc could then form planets, just as the discs around very young stars do.
In addition to BP Piscium, the astronomers have identified another old star with a dusty disc, called TYCHO 4144 329 2, which may have gone through a similar scenario.
The team has now observed the two stars with the Hubble Space Telescope, and are still analysing the results. They are also trying to make observations with the Chandra X-ray observatory.
"Chandra will hopefully tell us more about the ages of the systems," Melis told New Scientist. Younger stars have more X-ray activity than older ones.
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