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Press Release:

February 16 2005

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Images:

High resolution images and captions (NASA website)

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Weight Limits for the Biggest Black Holes

Chandra X-ray Image and Illustrations of the Lockman Hole

The very largest black holes reach a certain point and then grow no more, according to the best survey to date of black holes made by a group of University of Hawaii Astronomers using NASA's orbiting Chandra X-ray Observatory.

Amy Barger, Len Cowie, Wei-Hao Wang, and Peter Capak, from UH's Institute of Astronomy, in collaboration with three mainland astronomers, also discovered many previously hidden black holes that are well below their weight limit.

These new results show that the biggest black holes, those with at least 100 million times the mass of the Sun, ate voraciously during the early Universe. Nearly all of them ran out of 'food' billions of years ago and went onto a forced starvation diet.

On the other hand, black holes between about 10 and 100 million solar masses followed a more controlled eating plan. Because they took smaller portions of their meals of gas and dust, they continue growing today.

"Our data show that some supermassive black holes seem to binge, while others prefer to graze", said Amy Barger of the University of Wisconsin in Madison and the University of Hawaii, lead author of the paper describing the results in the latest issue of The Astronomical Journal (Feb 2005). "We now understand better than ever before how supermassive black holes grow."

Supermassive black holes themselves are invisible, but heated gas around them -- some of which will eventually fall into the black hole - produces copious amounts of X-rays in the centers of galaxies as the black holes grow. Since X-rays can penetrate the gas and dust that block optical and ultraviolet emission, the very long-exposure X-ray images with the Chandra satellite are crucial to find black holes that otherwise would go unnoticed.

For more information see:

• NASA press release "Weight limits for biggest black holes confirmed"
• University of Hawaii Institute for Astronomy
• NASA Chandra X-ray Observatory