M33
Image: Courtesy of ROBERT W. PROVIN and BRAD D. WALLIS

Astronomers at Rutgers University using the Hubble Space Telescope have spied something provocativetheyre just not sure yet exactly what it is. They suspect that M33, a galaxy they observed a mere three-million light years from our own Milky Way, may be the first ever seen to lack a supermassive black hole (SMBH) at its center. Or M33 houses the smallest black hole ever detected. The journal Science published their results online today.

David Merritt, Laura Ferrarese and Charles Joseph used Hubble data to calculate an upper limit for the size of a black hole in M33. They concluded that it could be no bigger than a slight 3,000 solar masses. "For the first time, we are able to put a constraint on a black hole, which is a thousand times or three orders of magnitude less massive than the least massive black hole that has been detected," Ferrarese says.

The Hubble observations agree with predictions based on a relationship that Ferrarese and Merritt proposed this past year. It states that the size of a black hole is related to the speed at which the stars in its galaxy are moving. The agreement, Ferrarese says, "implies that small black holes, if they exist, formed in much the same way as the very massive ones."

The researchers are hoping to obtain more time to use Hubble so that they can observe M33 further and unravel its black hole mystery. "Detecting black holes of only a few thousand solar masses is observationally challenging," Merritt says, "but it is critical for establishing how supermassive black holes relate to their host galaxies, and which mechanisms influence the formation and evolution of both."