Black Holes Tied to Galaxy Growth, Study Says

Stefan Lovgren
for National Geographic News
April 6, 2005

By peering into the deep belly of the universe, scientists have found that massive black holes are growing simultaneously with the galaxies in which they are situated.

Using powerful x-ray technology, astronomers surveyed distant galaxies more than ten billion light-years away. They found that the black hole in the center of each galaxy appears to be growing continuously throughout a burst of star formation.

The observations confirm a theory that the total mass of the stars in a galaxy corresponds to the mass of the black hole. The findings suggest that black holes are pivotal to the formation of galaxies and the structure of the universe.

Scientists have shown that pairs of galaxies—and their black holes—often merge together. At the time of such a merger, tidal forces drive a lot of gas toward the center of the galaxies. This gas feeds the black hole and also is available to create numerous stars.

"Although it is just a tiny fraction of the size of the galaxy, the black hole, in essence, [appears to be] able to control the [growth of the] galaxy," said David Alexander, a research fellow based at Cambridge University in England.

Alexander led the study, which appears tomorrow in the journal Nature.

Supermassive Black Holes

A black hole is a place in space where the gravity is so strong that nothing—not even light—can escape it.

There are two types of black holes. The most common are remnants of massive stars that have collapsed. Most galaxies have millions of such black holes.

The others are known as supermassive black holes, which reside at the center of each galaxy.

Scientists are not sure how these central black holes are created. But over the last decade researchers have found that the total mass of stars in galaxies corresponds directly to the size of their central black holes. This relationship suggests that galaxies and their black holes grow at approximately the same time.

To provide observational support for this theory, astronomers studied galaxies some 10 billion light years away. They used NASA's Chandra X-ray Observatory in Huntsville, Alabama, to find strong x-ray glows produced by hot gas swirling around the black holes.

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