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Supermassive Black Holes


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Artist's concept of a binary black hole pair.
Artist's concept of a binary black hole pair.
Black holes are objects that have a mass so concentrated in such a small volume that near them their gravity is strong enough that nothing, not even light, can escape. Scientists speculate that supermassive black holes millions or billions of times more massive than our sun dwell at the center of most, if not all, galaxies. Black holes, as the name suggests, do not emit any light, but their immediate surroundings can be intense sources of light. This light is generated by gas spiraling into the black hole and heating up enormously before falling in.

Galaxy types that harbor central black holes include spiral galaxies, like our own Milky Way, and elliptical galaxies. Spiral galaxies have a round, flattened shape, with a spiral arm structure and a bulge at the center. Ellipticals are oblong or spherical in shape and contain no arm structure. Many scientists believe elliptical galaxies are the product of violent past collisions between two or more spiral galaxies.

In one investigation, SIM Lite will track the bright "photocenter" generated by light from infalling gas onto the black hole in quasars and the centers of active galaxies. By making position measurements in different colors, it will be possible to distinguish the source of light coming from the cores of galaxies and quasars.

If two spiral galaxies merge into a single galaxy, their respective black holes would tend to sink toward the center and either merge or form a rotating pair, known as a binary system. SIM Lite will track the bright "photocenter" generated by light from infalling gas onto the binary black hole system in candidate galaxies. Just as a star's motion will help the mission detect planets, a moving photocenter will allow it to detect pairs of black holes circling each other - the "smoking gun" evidence of a past collision.
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