"Hidden" Black Holes Discovered in Distant Galaxies

Victoria Jaggard in Austin, Texas
National Geographic News
January 14, 2008

Displaying the cosmic equivalent of high metabolism, some skinny galaxies seem to have huge black holes hidden in their "stomachs," astronomers announced yesterday.

Skinny galaxies are slender disks that do not have big bulges of stars at their centers.

Until now, astronomers had thought such bulges were fundamentally connected to the growth of supermassive black holes believed to lie at the centers of most galaxies.

But the first survey of 32 skinny galaxies using infrared observations from the Spitzer Space Telescope revealed that some had the signatures of monstrous black holes at their cores.

"We discovered eight hidden feeding—or what we call active—black holes in completely unexpected places: in the centers of skinny galaxies," lead study author Shobita Satyapal told reporters at a meeting of the American Astronomical Society (AAS) in Austin, Texas.

"This constitutes the best evidence yet that a bulge is not necessary for a black hole to form and grow."

Symbiotic Growth

Galaxies come in all shapes and sizes, noted Satyapal, an astronomer at George Mason University in Virginia.

Elliptical galaxies resemble fluffy balls of stars and gas that are themselves massive bulges. Spiral galaxies are disks that can exist with or without fat bulges at their centers.

Previously, scientists had noticed that almost every galaxy with a bulge harbors a supermassive black hole, and that the mass of a galaxy's black hole is roughly equal to the mass of its bulge.

This suggested that the two must develop together, like a pair of symbiotic species. The correlation meant that skinny galaxies shouldn't have central black holes.

But galaxies with little or no bulge have lots of gas and dust in their middles that obscure visible light, Satyapal said. So her team examined nearby skinny galaxies in infrared, which can penetrate the haze.

Continued on Next Page >>




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