Listen to the UVA Today Radio Show report on this story by Fariss Samarrai:
January 9, 2011— Astronomers have discovered a supermassive black hole in the center of a tiny low-mass galaxy, suggesting the formation of supermassive black holes may precede the growth of galaxies. This finding challenges conventional wisdom that supermassive black holes only inhabit massive galaxies with voluminous spheroidal components called "bulges."
The scientists found the supermassive black hole in a dwarf galaxy, known as Henize 2-10, which is undergoing a violent burst of star formation. This star-creating miniature galaxy is believed to be analogous in many ways to infant galaxies in the early universe.
The finding will be reported in the Jan. 9 online edition of the journal Nature and presented Jan. 10 at the annual meeting of the American Astronomical Society in Seattle.
"We never expected to find a supermassive black hole in Henize 2-10," said lead author Amy Reines, a Ph.D. candidate in astronomy in the University of Virginia's Graduate School of Arts & Sciences. "We may be witnessing an early stage of galaxy and black hole evolution that has not been observed before."
Normally, supermassive black holes are found in much larger galaxies that have a bulge or a nuclear star cluster. Henize 2-10 has neither. The discovery, Reines noted, will enable astronomers to gain insight into how the first supermassive black holes may have been formed very early in the history of the universe.
Supermassive black holes, gravitational monsters reaching masses upwards of a billion times more than our sun, are among the most exotic and enigmatic objects in the known universe – yet they commonly reside in the center of normal galaxies like our own Milky Way, as well as in even larger galaxies. More massive galaxies generally have more massive black holes, and it is thought that black holes and their host galaxies have grown synchronously over cosmic history.
The discovery of a supermassive black hole in Henize 2-10 challenges this notion and suggests that the formation of supermassive black holes may actually predate the build-up of their host galaxies. Reines will search for other examples like Henize 2-10 to help refine theories as to how supermassive black holes form.
Although no light can escape from a black hole itself, astronomers are able to determine their presence based on the behavior of matter in their vicinity. In our own galaxy, astronomers have established the presence of a supermassive black hole by observing the orbits of nearby stars. A black hole also can be identified by different types of light originating from superheated material swirling around these mysterious regions.
Though Henize 2-10 has been heavily studied for decades due to its extreme star formation activity, its central supermassive black hole went unidentified until Reines and her colleagues serendipitously found it during a study of dwarf starburst galaxies. They discovered evidence of the supermassive black hole after analyzing several kinds of light emanating from Henize 2-10 spanning radio to X-ray wavelengths. The observations of Henize 2-10 were taken with the Very Large Array, the Hubble Space Telescope and the Chandra X-Ray Observatory.
Reines' collaborators include U.Va. astronomy research associate Gregory Sivakoff, U.Va. astronomy professor Kelsey Johnson and National Radio Astronomy Observatory astronomer Crystal Brogan.