Weekly Science Update

Wednesday, January 03, 2007
The Gestation of Massive Stars
Astronomers think that most stars form in clusters because evidence suggests that a nursery capable of producing one star efficiently is usually capable of birthing many. But precisely how this happens is still unclear. If our own Sun, for example, had formed in such a cluster, where are its siblings? The molecular cloud NGC 6334, located about five thousand light-years from Earth, is apparently in the process of giving birth to two separate clusters of massive stars. Astronomers have reported two regions of activity, each with a total mass of a few hundred solar masses, each about the size of our solar system (measured at its cometary edges), and each with several young stars. Discoveries made by the Submillimeter Array (SMA) last year included small, star forming cores embedded in these regions in NGC 6334; astronomers are now probing these regions with other instruments to try to unravel more clues about how star clusters form.

Two SAO astronomers, Luis Zapata and Paul Ho, together with a colleague, have used radio telescopes to follow up the SMA results. They report finding elongated disks around four of the embedded stars, and are able to estimate the disks' masses. What they find is a surprise: in the few previous cases where disks have been adequately studied around such stars, they are typically ten times smaller in mass than the star itself. But in each of the four objects studied in NGC 6334, the disk appears to be more comparable to the star's mass. The authors note that young stars will grow in mass as they accrete material from the disk, and suggest that perhaps these stars are still very young. Theoretical modeling, while not accounting for all of the likely subtleties, indicates the range of masses seen in the NGC 6334 cores may be reasonable. The new results, therefore, suggest that these very young stars are still early in the process of growing, and that astronomers have succeeded in obtaining what might be considered an analog of a ultrasound scan of the stellar embryos in this interstellar womb.

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