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The center of the Milky Way galaxy is a forbidding place, dominated by what astronomers strongly suspect is a black hole four million times the mass of the sun. But a new study provides evidence that stars are able to form there, despite the violent conditions stirred up by the supermassive gobbler.
The findings indicate that the clouds of gas at the galaxy's core must be denser than previously believed to coalesce into stars while resisting being ripped apart by the black hole's gravitational pull. Study leader Elizabeth Humphreys, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., presented the results yesterday at the semiannual meeting of the American Astronomical Society in Long Beach, Calif.
There are many stars in orbit around the Milky Way's suspected supermassive black hole—two teams even tracked their orbits recently to better determine the black hole's properties. But, Humphreys said, no one knows whether the stars observed near the black hole originated there or if they migrated from other, calmer locations in the galaxy. Her team's study supports the local-birth theory.
Humphreys said the results, which uncovered what appear to be two young stars as close as seven light-years from the galactic center, were surprising, as that is "one of the last places ... you would expect to find stars forming."
To locate these candidate protostars, Humphreys and her colleagues used the Very Large Array of telescopes near Socorro, N.M., to look for water masers near the black hole. These masers, sources of microwave radiation analogous to lasers, often serve as markers of star formation.
Turning up 12 such masers, Humphreys and her colleagues took what she called "a really conservative approach" to rule out those radiation sources that had features associated with older stars. That left two protostar candidates "right at the heart of the galactic center," as Humphreys put it, pointing to a denser molecular environment near the galaxy's core than expected.
Image credit: NASA, ESA, and A. Schaller (for STScI)
