Black holes shed light on galaxy formation

By Ker Than

Staff Writer

updated 1:55 p.m. ET Feb. 21, 2007

Black holes are dark secrets, shrouded in churning spacetime and scrunched into points smaller than an atom. In recent years, astronomers have successfully penetrated some of their mysteries, but fundamental questions about what they are and how they work are still unanswered.

SPACE.com asked several black hole experts what tops their list of recent black hole discoveries and what they think the biggest questions surrounding these captivating objects are.

Several of the scientists interviewed said the single most profound discovery to emerge in their field in recent years is the intimate link that appears to exist between supermassive black holes and their host galaxies. This idea is sometimes called co-evolution.

“We have come to realize that massive black holes in galaxies are central players in the story of how entire galaxies assemble,” said Christopher Reynolds, a black hole researcher at the University of Maryland. “This is a very surprising aspect of the universe that we are just starting to learn about.”

“Ten years ago the idea that a supermassive black hole at the center of our galaxy might exist was just a possibility,” said Andrea Ghez of UCLA. “Thanks to advances in high-resolution imaging technology, this idea has become almost a certainty.”

Supermassive black holes are thought to have masses equal to millions or even billions of suns. Recent studies have found that black holes and galaxies can affect each other’s formation and evolution.

“This started locally with the discovery of the very close correlations between the masses of black holes and the properties of their host galaxies, and then moved on to the realization that galaxy formation and star formation had to be partly controlled by the effects of black holes and accretion,” said Christopher Kochanek of Ohio State University.

While scientists have yet to observe a black hole directly, they have spotted X-ray radiation created by friction near the event horizon, the perimeter around a black hole beyond which nothing, not even light, can escape.

“This is an amazing achievement,” Reynolds said. “Through these observations, we already have strong evidence for the significant slowing of time close to a black hole as well as the ‘tornado-like’ motion of spacetime induced by black hole spin.”

But there is still plenty of room for improvement. “There are lots of things (about black holes) that we’d like to measure or measure better to confirm what we think,” Kochanek said. “That is the biggest frustration.”

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