March 14, 2001. Copyright 2001. Graphic News. All rights reserved.

Giant black holes ruled primordial x-ray universe

LONDON, March 14, Graphic News: SUPERMASSIVE black holes once dominated the universe, sucking in gas, dust and whole stars and erupting with surges of X-rays that have journeyed for billions of years through space.

Using the $1.5 billion orbiting Chandra X-Ray Observatory, astronomers focused on small sections of the sky -- about one-quarter the size of the full moon -- making days-long exposures to capture faint X-rays streaming from more than 12 billion light-years away.

ÒThe Chandra data show us that giant black holes were much more active in the past than at present,Ó said Riccardo Giacconi, a Johns Hopkins University astronomer.

ÒIf you look at the sky with X-ray eyes, you see almost nothing but black holes,Ó Bruce Margon, an astronomy professor at the University of Washington in Seattle, said.

Black holes, once the imaginings only of theorists, are now thought by most astronomers to exist by the hundreds of billions -- from supermassive ones at the gravitational core of most galaxies, to smaller ones that are the remains of collapsed stars.

Experts say the Chandra deep field study confirms theories by showing that the early universe teemed with active black holes, spewing X-rays across the heavens.

A black hole is an extremely dense object at the center of a galaxy with such powerful gravitational pull that not even light can escape. That is why black holes are invisible to conventional telescopes that use visible light.

Extremely powerful black holes at the center of galaxies -- known as Òquasi-stellar radio sources,Ó or quasars -- can have a mass ranging from one million to 100 billion times that of the sun, concentrated at a point not much bigger than Earth. The high energy they emit -- about 10 trillion times as much energy per second as the Sun -- comes from the force of enormous energy released by matter that falls into black holes.

Stellar black holes, formed from collapsed stars, are much smaller, down to three solar masses, and can have a core only a few miles across.

Since they allow no light to escape, black holes are detected by the effect that they have on surrounding gas, dust and stars. Before matter is pulled into the center of a black hole, it is accelerated to near the speed of light, creating millions of degrees of heat and sending out streams of X-rays.

Included in the images of the Chandra deep field is the first confirmation of the existence of extremely exotic star-like objects, so-called ÒburiedÓ quasars.

These shy quasars have for years been suspected to exist, but have been unseen by visible light telescopes because they are buried deeply in clouds of dust and gas.

X-rays penetrate such clouds, and Chandra was able to pinpoint the first buried, or type II quasar. The discovery of this object, some 12 billion light years away, is key to understanding how dense clouds of gas form galaxies with massive black holes at their cores.
/ENDS 
Sources: NASA, Harvard-Smithsonian Center for Astrophysics, Associated Press, Reuters