Alternate Names

NGC 221

Type

Supermassive

Location

in the constellation Andromeda

Finder Chart

Distance

2.4 million light-years (0.81 megaparsecs)

Mass

3 million times the mass of the Sun

Size

Diameter about 10 million miles -- about 12 times the diameter of the Sun

Discovery Methods

• Measuring the motions of stars

Measuring the motions of stars

Because a black hole is both massive and compact, it exerts a strong gravitational pull on the material around it. Astronomers can deduce the presence of a supermassive black hole in the core of a galaxy by measuring the velocities of stars that orbit the black hole. A more-massive black hole will accelerate nearby stars to greater speeds, so the velocities of stars can reveal not only the presence of a black hole, but its mass as well.

More about black hole discovery methods »

This document was last modified: November 19, 2009.