It is my pleasure to introduce Dr. Eric McKenzie, associate director for the department of astronomy at the University of Maryland. He received his Ph.D. from the University of Florida, and his research has focused on galaxy evolution at specific wavelengths of redshifted light. He also helped me get some of my facts straight for the Tomorrow News Network story “The Orion War.”
This week, he will be answering questions about galaxy evolution and what the early universe was like.
James Pailly: What are quasars, how did they form, and what role did they play in galaxy evolution?
Dr. McKenzie: Quasars are the bright centers of galaxies where hot gas is swirling into giant black holes. We believe that nearly all galaxies have massive black holes at their center; the Milky Way certainly does. In most cases, these black holes are quiescent. They’re not actively absorbing much material because the galaxy’s gas and stars are orbiting around the black hole without falling in. However, a small fraction of galaxies have active black holes, where material is continuously spiraling inward. The gas is moving very quickly in tight orbits and heating up due to friction between the gas particles. The net result is a powerful blaze of energy – a quasar. When the clump of gas is eventually consumed, the quasar will turn off again.
Quasars are a feature of the early universe – we don’t generally see them in nearby galaxies. This may be because, at our present stage in the universe’s history, the massive black holes at the centers of galaxies have already cleaned out all of the ‘easy pickings’ of gas clouds.
The effects of quasars are potentially powerful enough to affect the evolution of their host galaxies. As most of the nearby gas swirls into the black hole, angular momemtum effects cause a small fraction to be flung outward instead. This outflow may push away other gas which is farther from the galaxy’s center, perhaps eventually cutting off the quasar’s food source. On a larger scale, it may even reduce the galaxy’s ability to concentrate gas to form new stars. This is a very active area of current research!