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Stars Come Out at Astronomy Meeting

10 June 2009 (All day)
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(top left) University of Hawaii Institute for Astronomy; (top right): A. Dupree (CfA)/NASA/ESA; (bottom) NASA/JPL-Caltech/S. V. Ramírez (NExSci/Caltech)/SST/IRAC/MIPS/IRS

Star delights. Counterclockwise from bottom: Researchers have spotted three baby stars at the center of the Milky Way, discovered a large molecular cloud that they believe will turn into a massive star, and watched a red supergiant, Betelgeuse, shrink in diameter.

PASADENA, CALIFORNIA--Stars have been the, well, stars here this week at the semiannual meeting of the American Astronomical Society. Scientists are learning a lot more about how nearby suns form--and how they die. Here are some highlights from the conference:

Violent stellar birth. Researchers have, for the first time, spotted baby stars in the chaotic center of our Milky Way galaxy, not far from a black hole. Astronomers Solange Ramírez and Deokkeun An of the California Institute of Technology in Pasadena analyzed infrared spectra of the galactic center taken by Spitzer, one of NASA's space-based telescopes. They found three objects with spectra bearing the imprints of warm gases such as acetylene and hydrogen cyanide, which are present in the early stages of stellar evolution. That means the objects are infant stars, located barely 200 light-years from the edge of the galaxy's black hole.

The finding suggests that mature stars found near the black hole by other researchers may have originated there despite the violent conditions, says Ramírez, who presented her findings at a press conference on Wednesday. How stars could form in such an environment remains a mystery, she says.

Making a massive star. How do superheavy stars, more than eight times the mass of the sun, form? Researchers have been debating whether these highly luminous objects are seeded by a multitude of small stars or if they are born directly from the collapse of a gigantic cloud of molecular gas. Results presented at the meeting yesterday by Jonathan Swift, an astronomer at the University of Hawaii, Manoa, suggest that it could be the latter.

Using the Submillimeter Array atop Mauna Kea in Hawaii, Swift and his colleagues recently found a type of object that had never been seen before: an extremely large cloud of cold, dense gas 23,000 light-years away. The cloud is 120 times more massive than the sun, is packed within a relatively small volume, and has an extremely low temperature of barely 18 degrees above absolute zero. The conditions are just right for it to eventually collapse into a star, Swift says.

A shrinking giant. One of the most famous stars in the universe seems to be on a slimming diet. Researchers from the University of California, Berkeley, reported yesterday at the meeting that Betelgeuse--a red supergiant that, back in 1921, was the first star ever to have its size measured--has steadily shrunk in diameter by 15% over the past 15 years. It's not clear why, although one possibility is that the star is on its way to dying a spectacular death as an exploding supernova.

Red supergiants are the largest type of star known, and Betelgeuse, part of the Orion constellation, is a formidable member of that class. If it replaced our sun, its edge would sizzle Jupiter. It is not unusual for stars to wax and wane in size over cycles of one to a few years, but this is the first time that a red supergiant has been seen shedding size so dramatically over an extended period. "Maybe there's some instability in the star and it will collapse soon," says Edward Wishnow, who has been monitoring the star since 1993.

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