Survey: Cosmos Packed With Black Holes

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

Mushotzky, also with NASA's Goddard center. "Perhaps as much as 20 percent of all of the radiated energy in the universe arises in one way or another from AGN activity."

Another phenomenon of black holes is the the jetting of highly energetic particles, which are commonly seen radiating from quasars and other objects at nearly the speed of light.

Scientists have long debated whether the long streams, which can flow for hundreds of thousands of light-years across the sky, contain protons, their antimatter partners positrons, or a mix of electrons and protons.

New research concludes the streams are made up of protons and electrons. The jets are believed to be one of the primary methods for redistributing matter and energy in the universe.

"Black hole jets are one of the great paradoxes in astronomy," said NASA's Rita Sambruna, also with Goddard. "How is it that black holes, so efficient at pulling matter in, can also accelerate matter away at near light speed? We still don't know how these jets form, but at least we now have a solid idea about what they're made of."

The research was presented this week at the American Astronomical Society meeting in San Francisco.