In the constellation Leo Minor
160 to 260 million times the mass of the Sun
Diameter roughly equal to the diameter of Jupiter's orbit around the Sun
Observations by Hubble Space Telescope show that a disk of gas and dust in the center NGC 3245 is orbiting something small, dark, and heavy -- most likely a supermassive black hole that is roughly 200 million times the mass of the Sun.
NGC 3245 is classified is a lenticular galaxy, which means it is shaped somewhat like a lens -- a round disk that is thick in the middle and tapers away at the edges. Such a galaxy has less gas and dust than disk-shaped galaxies like the Milky Way, but more than elliptical galaxies, which have consumed almost all of their gas and dust to make stars.
A team led by Aaron Barth of the Harvard-Smithsonian Center for Astrophysics obtained a series of observations of NGC 3245 with HST's Space Telescope Imaging Spectrograph (STIS), which space shuttle astronauts installed aboard the orbiting observatory in 1997.
STIS allowed the astronomers to take spectra at several different locations in NGC 3245 simultaneously. From these observations, the astronomers could measure the motions of gas and dust at different distances from the galaxy's core. The observations showed that the gas moved fairly slowly at great distances from the core but much faster closer in -- accelerated by the gravity of a small, dark, heavy mass.
The dark mass most likely is a supermassive black hole. The observations, however, didn't probe deeply enough into the galaxy's nucleus to rule out other explanations, such as clusters of smaller black holes, neutron stars, or white dwarfs. "For most claimed BH [black hole] detections," the astronomers wrote in a 2001 paper announcing the discovery, "including NGC 3245, the conclusion that the massive dark object is a BH still rests on circumstantial evidence and on the expectation that a supermassive BH ought to be present in the nuclei of most massive galaxies."
Observations by radio telescopes show that the likely black hole is moderately active, suggesting that a disk of superhot gas encircles the black hole, and that some of the gas is funneled into "jets" of particles by magnetic fields. The space-based Chandra X-Ray Observatory has detected X-rays coming from NGC 3245, further supporting the idea of an accretion disk encircling a supermassive black hole.
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This document was last modified: March 14, 2012.