Oct. 6, 2006 — Our cosmic neighborhood is flush with supermassive black holes busily devouring nearby stars and other matter, say scientists who this week unveiled the first complete census of black hole activity in the local universe.
The survey, which took nine months of observations with NASA's Swift satellite, uncovered more than 200 supermassive black holes within 400 million light years of Earth, said Jack Tueller with NASA's Goddard Space Flight Center in Greenbelt, Md.
These objects, also known as Active Galactic Nuclei or AGN, are millions or even billions times as large as the sun and occupy a region of space about the size of our solar system.
As they gobble up nearby matter, the black holes generate X-rays, as well as many other forms of light. Other black holes also spew out jets of particles, which a related research project has determined are made up of protons and electrons.
Despite their violent activity, many AGN are obscured by surrounding gas and dust.
Swift, a satellite whose main mission is to track gamma ray bursts, spends its off-hours scanning the sky for high-powered X-rays. This radiation can be detected despite light-absorbing material which often hides the black holes.
"It's hard to believe the whole sky is peppered with black holes," said University of Maryland researcher Craig Markwardt.
Scientists know that nearly every massive galaxy, including our own Milky Way galaxy, has a supermassive black hole near its center, but they do not know why only a few percent of them appear to be actively consuming matter.
Most black holes, including our own, are dormant and were not surveyed in the Swift census. But those black holes that are active play a key role in the universe.
The survey will help scientists understand one of the fundamental processes by which energy is distributed in the universe.
"You can't understand the universe without understanding black holes," said Richard
