Ultraluminous sources in NGC 253
Credit: X-ray: NASA/SAO/CXC, Optical: ESO

Gathering of Black Holes?

Many if not most galaxies are thought to contain super massive black holes in their centers. These supermassive black holes contain the equivalent mass of millions of stars, and in extreme cases, they produce incredible amounts of radiation by swallowing stars and gas in their neighborhood. It's a mystery though how these supermassive black holes form - do they act as the seed around which the rest of the galaxy forms, or does the galaxy form first, and are the supermassive black holes built up gradually from relatively small mass objects over a period of time? An observation of the galaxy known as NGC 253 by the Chandra X-ray observatory may have provided an important clue. NGC 253 is a "starburst" galaxy, in which large numbers of massive stars form over a relatively brief period of time. The image above shows an optical image of NGC 253, along with a zoomed X-ray image of the core of NGC 253, shown in the inset in the upper right. The sharpness of the new Chandra observation has enabled astronomers to locate six so-called "superluminous X-ray sources" in NGC 253. These superluminous sources are so bright in X-rays that they are very likely "medium-mass" black holes, black holes with a mass of hundreds of solar masses, visible as bright sources in the inset X-ray image. Interestingly four of the six ultraluminous sources lie very near the core of the galaxy, within only 3000 light years. Astronomers suspect that these medium mass black holes are "falling" towards the center of the galaxy, and if so they will eventually combine to form a single, more massive black hole. Are these medium mass black holes the building blocks out of which a supermassive black hole is made?

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Page Author: Dr. Michael F. Corcoran
Last modified July 16, 2001