in the constellation Ursa Major
120 million light-years
23 million times the mass of the Sun
Slightly larger than Mercury's orbit around the Sun
NGC 3516 is a disk-shaped galaxy, which is tilted so that it appears nearly face-on. At this angle, telescopes have a clear view down into the bright core of the galaxy, where astronomers suspect that a large black hole resides. Gas clouds are being pulled inwards by the gravity of the black hole, swirling around and around before being swallowed up. The violent motions in this central region create a great deal of heat, and as a result, the gas glows brightly in nearly every part of the electromagnetic spectrum, from X-rays to infrared light.
One especially interesting set of observations of NGC 3516 was made with the orbiting XMM-Newton X-ray observatory. In addition to a steady, bright X-ray glow from the hot gas surrounding the black hole, pulses of X-ray energy appear every 5.5 hours, starting off at lower frequency and shifting to higher frequency before disappearing. This strange pulse pattern comes from an extra-hot spot within the gas, which appears to change its frequency as it whirls around the central black hole. Researchers estimate that this hot spot is only 300 million miles from the black hole, and thus must be travelling at 22 million miles per hour, or seven percent of the speed of light.
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This document was last modified: November 19, 2009.