Who ate all the planets? Blame the 'bloatars' - space - 10 February 2011 - New Scientist

WHEN stars put on weight, it really shows. A group of oddly bloated stars may have grown fat by eating their own planets in a feeding frenzy.

No one has ever seen anything quite like the nine stars spotted by the Hubble Space Telescope in a young cluster called NGC 3603. They are too cool to be ordinary stars, with analysis of their infrared light emissions indicating surface temperatures between 1700 and 2200 kelvin. By this measure, they are more like brown dwarfs, objects intermediate in mass between planets and fully fledged stars.

Yet brown dwarfs are dim objects that should be too faint to detect at the cluster's distance from Earth - 20,000 light years. "We were quite puzzled," says Loredana Spezzi at the European Space Agency in Noordwijk, the Netherlands.

Now Spezzi and her colleagues have another explanation. They think the enigmatic objects are part of stellar systems that spawned planets - then hastily devoured them.

Some planets are thought to spiral in towards their stars. That would explain why so many alien worlds have been found in star-hugging orbits. The team says that some may spiral so close that the star "eats" them - the star's gravity rips the planet apart and captures its debris.

This captured debris would form a temporary outer atmosphere for the star, which would be cooler than the star's normal light-emitting surface, explaining the apparent low temperatures of the nine mysterious objects.

These bloated stars, or "bloatars", would also be bigger and brighter than brown dwarfs, explaining how they could be seen at such a great distance, the team says in a paper to appear in The Astrophysical Journal (arxiv.org/1101.4521).

Astronomers have previously found a few cases of stars with odd properties that might be explained by planet-eating, including stars containing unusually large amounts of lithium, possibly a consequence of feasting on planets containing the element. But these bloatars are the first example of a feeding frenzy, with many stars in the same cluster all devouring planets.

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