Planet-Sized Snacks

17 September 2003 (All day)

Glutton. Astronomers think that V838 Monocerotis gobbled up three Jupiter-sized planets.

The mysterious flashes of the star V838 Monocerotis (V838 Mon) have puzzled astronomers for more than a year. Now a research team says the flashes may be signs that the star gorged on three planets in close orbit. If so, it would be the first time astronomers have caught a star in such an act of gluttony--one that may eventually doom our own planet.

In January 2002, V838 Mon went from a faint speck of light to a beacon 600,000 times more luminous than our sun (ScienceNOW, 26 March). In the 2 months following the first burst, the star brightened twice again, even more strongly than before, behaving unlike any known type of star. Astronomers suggested that the flashes could have been sparked by two colliding stars or by a star that exploded after sucking hydrogen fuel from a companion star.

But astrophysicist Alon Retter of the University of Sydney, Australia, and colleague Ariel Marom noticed that all three of V838 Mon's outbursts were very similar, with each flash followed by a dimming and then a weaker secondary flash. That suggested to them that the same phenomenon was behind all three flashes. In a paper accepted by the Monthly Notices of the Royal Astronomical Society, they suggest that as the star expanded with age, it engulfed three planets in succession. Based on observations, they calculate that these worlds must have been Jupiter-sized and in close orbits. In this scenario, the first planet would feed fresh hydrogen into its star's core, with bomblike results, driving further expansion to gulp down another planet, and then another. "We believe that this is the first time that a star was caught in the act of swallowing planets," Retter says.

Other scientists are skeptical. "Each of the proposed models has severe problems, and this includes this present one as well," says astrophysicist Noam Soker of the Technion-Israel Institute of Technology in Haifa, who with Romuald Tylenda of the Nicolaus Copernicus Astronomical Center in Warsaw, Poland, first proposed that V838 Mon experienced a stellar merger. Soker says it's unlikely, although not impossible, that such a star would have three planets of similar mass all in close orbit. Still, he's fascinated by the prospect of planets influencing stellar evolution.

Related sites
Alon Retter and Ariel Marom's paper
The American Association of Variable Star Observers' site on V838 Mon
More Hubble Space Telescope pictures of V838 Mon

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