Alternate Names

NGC 224

Type

Supermassive

Location

in the constellation Andromeda

Finder Chart

Distance

2.5 million light-years (0.78 megaparsecs)

Mass

30 million times the mass of the Sun

Size

Diameter roughly equal to the orbit of Venus.

Discovery Methods

• Measuring the motions of stars

M31

Our home galaxy, the Milky Way, is part of a collection of about three dozen galaxies known as the Local Group. These galaxies move through space as a single unit bound together by their mutual gravitational pull.

The largest member of the Local Group is the Andromeda Galaxy, M31. Like the Milky Way, Andromeda is a giant spiral galaxy, so it looks like a pinwheel spinning through space. It spans about 125,000 light-years, and contains several hundred billion stars. At a distance of about 2.4 million light-years, it is the closest large galaxy to the Milky Way, and the only one that is visible to the unaided eye.

Using telescopes on the ground and in space, astronomers discovered two large clumps of stars that appear to form a "double nucleus" in M31. The two bright clumps that form this double nucleus are actually the brightest regions of a disk of stars that completely encircle a supermassive black hole. From measuring the speeds at which these stars orbit the center of the galaxy, astronomers deduce that the black hole is about 30 million times as massive as the Sun and roughly 10 times as massive as the central black hole in the Milky Way.

In 2006, the disk of superhot gas around the black hole flared up, producing 100 times more ray energy than it had before. It soon settled down, but continued to produce 10 times more X-ray energy than before the outburst. Astronomers say the outburst may have been generated by the disk's powerful magnetic field. Line of magnetic force tangled then snapped, sending energy and charged particles into space in a process similar to the one that produces flares and other outbursts on the surface of the Sun.

M31's black hole is the second supermassive black hole discovered in the heart of a galaxy. The first was found in M32, a small satellite galaxy to M31.

References

Supermassive Black Hole Discovered in Andromeda Galaxy

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This document was last modified: May 28, 2010.