Secrets of Supermassive Black Holes Revealed

These images, taken with the 2.1-meter telescope at Kitt Peak National Observatory in Arizona, show galaxy shapes that are either physically intertwined or distorted by the gravity of nearby neighbors.

These AGN were known prior to the Swift survey, but Swift has found dozens of new ones in more distant galaxies. Credit:

NASA/Swift/NOAO/Michael Koss and Richard Mushotzky (Univ. of Maryland)

Researchers had scratched their heads over why such high-energy displays occurred, until now. The findings announced today confirm past theories that suggested that violence from galactic mergers can fuel the growth of central black holes.

"We find that about 25 percent of black holes found by Swift are in the process of merging," said team member Michael Koss of the University of Maryland in College Park, during a NASA teleconference.

About 60 percent of such active galaxies will merge completely within the next billion years to create giant black holes.

Hard X-ray action

Swift used its Burst Alert Telescope (BAT) to detect any telltale signs of hard X-rays, which rank between gamma-rays and X-rays on the electromagnetic spectrum of light.

Such hard X-rays can pass through interstellar gas or dust which otherwise blocks ultraviolet, optical and soft-X-ray light. Infrared radiation can also pass through the material, but may represent emissions from a galaxy's star nurseries rather than the central black holes.

The hard X-ray survey allowed astronomers to feel confident that they had spotted the majority of AGN within Swift's survey range of about 650 million light-years away. (A light-year is the distance that light can travel in one year — about 6 trillion miles (10 trillion km).)

Koss and his colleagues then followed up by spending 20 nights peering at the AGN with a 2-meter telescope at Kitt Peak National Observatory near Tucson, Ariz.

"Many of these galaxies are very close to us, so we see the severe distortion of the galaxy shapes," Koss explained. "In addition, we see that the galaxies are very close to each other and therefore will merge and interact very strongly."

Like good neighbours do!