LONG BEACH, CALIFORNIA--The intense gravity of black holes ought to rip nearby star-forming clouds to shreds. Yet stars still form in their vicinity. Researchers now have a possible explanation for the paradox: gas clouds that are dense enough to hang together in defiance of a black hole's violent pull.
The findings come thanks to observations around the gigantic black hole that sits at the heart of the Milky Way. This cosmic beast is 4 million times more massive than the sun, yet stars have been discovered just a few light-years away. To figure out how they form, astronomer Elizabeth Humphreys of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and her colleagues peered into the heart of the galaxy with the help of the Very Large Array of radio telescopes spread throughout the continental United States.
Searching for a specific kind of radio signal known as a water maser--a clue to star birth--the researchers discovered two infant stars 7 and 10 light-years from the galactic center that hadn't been observed before. The signal also showed that the density of gas in the region was anywhere between 10 and 1000 times greater than previously thought.
"The gas is so dense that its self-gravity helps to overcome the shredding effect of the black hole," says Humphreys, adding that models of our galactic center should now be revised with this new density taken into account. The researchers say the finding is consistent with results from recent computer simulations of star formation in the neighborhood of a massive black hole.
Q. Daniel Wang, an astronomer at the University of Massachusetts, Amherst, says the work offers a great example of how the peculiarities of the environment can allow stars to form where they might not be expected. What appears to be happening in the galactic center, he says, is a tug of war between gas clouds and the black hole in which some of the clouds "come out as winners."