Hole power

Ron Cowen

More evidence has emerged that supermassive black holes wield influence far beyond the grasp of their gravity.

Five years ago, astronomers discovered that the core stars of a galaxy always weigh about 500 times as much as the galaxy's supermassive black hole (SN: 1/22/05, p. 56: Available to subscribers at http://www.sciencenews.org/articles/20050122/bob8.asp). That correlation seemed astonishing because a black hole's pull extends less than a light-year from the galactic core, whereas the stars lie up to 20,000 times that distance.

A computer model described in the Feb. 10 Nature suggests how black holes can affect distant stars. The simulation follows the merger of two young galaxies, each with its own central black hole. As the melding proceeds, the black holes combine and then swallow surrounding gas. But some of the energy emitted by the infalling gas spawns a quasar. Fierce winds from the quasar disperse star-forming gas lying far beyond the black hole's vicinity. This process quenches star formation and so shapes the galaxy. Driving away the gas also shuts down the quasar.

Observations with NASA's Chandra X-ray Observatory support this model. Amy Barger of the University of Wisconsin–Madison and her colleagues used Chandra to detect dozens of black holes. They found that supermassive black holes weighing less than 100 million suns are buried under large amounts of dust and gas, but that larger black holes lie amidst much less material. That's an indication that the more-massive holes have stronger winds that push away surrounding gas and dust, Barger's team notes in the February Astronomical Journal.

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References:

Barger, A.J., et al. 2005. The cosmic evolution of hard x-ray selected active galactic nuclei. Astronomical Journal 129(February):578–609. Abstract available at http://dx.doi.org/10.1086/426915. Preprint available at http://arxiv.org/abs/astro-ph/0410527.

Di Matteo, T., V. Springel, and L. Hernquist. 2005. Energy input from quasars regulates the growth and activity of black holes and their host galaxies. Nature 433(Feb. 10):604–607. Abstract available at http://dx.doi.org/10.1038/nature03335.

Further Readings:

Cowen, R. 2005. The hole story. Science News 167(Jan. 22):56–58. Available to subscribers at http://www.sciencenews.org/articles/20050122/bob8.asp.

For further information on supermassive black holes, go to http://chandra.harvard.edu/photo/2005/bhlock/.

Sources:

Amy J. Barger
University of Wisconsin, Madison
Department of Astronomy
475 North Charter Street
Madison, WI 53706

From Science News, Volume 167, No. 10, March 5, 2005, p. 158.