In the constellation Sagittarius
4.1 million times the mass of the Sun
Diameter roughly 15 million miles (24 million km).
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: February 12, 2012.