NGC 4395

At a distance of just 14 million light-years NGC 4395 is a close galactic neighbor. That should make its central black hole one of the easiest to study. Unfortunately, though, there's not much to see. The black hole is one of the least massive yet detected in the center of a galaxy, and it also is one of the quietest.

NGC 4395 is classified as an AGN (active galactic nucleus) galaxy, indicating that its core is emitting large amounts of energy. The source of the energy is usually a supermassive black hole surrounded by a a hot, active accretion disk.

In 2003, studies of the motions of stars around the galaxy's nucleus suggested the presence of a supermassive black hole, but one that was unusually small. Follow-up studies with Hubble Space Telescope allowed astronomer to pin down the black hole's mass at 360,000 times the mass of the Sun.

Observations with a network of radio telescopes revealed the presence of material flowing outward from the accretion disk, squirting about one light-year away from the black hole.

NGC 4395 is a small spiral galaxy with no central "bulge" of stars. Such galaxies are expected to have either no central black hole or a small one, because there appears to be a mechanism in which the central bulge feeds gas and dust to the black hole, causing it to grow. With no bulge, there should be no ready food supply for the black hole. So the small black hole in NGC 4395 may help astronomers understand how supermassive black holes form — perhaps from small "seed" black holes that later grow to enormous proportions.

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This document was last modified: July 8, 2013.