SCIENCE

Sixteen Years of Black Hole Watching Pays Off

How do you prove that a black hole exists? It is so dense, not even light can escape its grasp

December 10, 2008

How do you prove that a black hole exists? It is so dense, not even light can escape its grasp. It cannot be seen.

To find a black hole, you track the movement of the stars orbiting and moving near the object, and you do this for many years. You’ll need a big, powerful telescope (such as the W.M. Keck Observatory in Hawaii or the Very Large Telescope in Chile), and you will have to figure out how to compensate for the distortion caused by the earth’s atmosphere (adaptive optics). But patience has its rewards.

For years, two teams have been studying the supermassive black hole at the center of the Milky Way, Sagittarius A*. The team led by Reinhard Genzel of the Max-Planck-Institute for Extraterrestrial Physics in Garching, Germany, has just released the results of their 16 years of observations of 30 stars near the black hole. By their calculations, Sagittarius A* is 27,000 light years away and about four million times as massive as our Sun (it’s much more dense, though, which is what makes it a black hole).

The ESO, which runs the Very Large Telescope that Genzel’s team used, produced a brief video explaining the research. It has some nice animations of the stars orbiting the black hole. They don’t explain adaptive optics, though. For that, you should read Homing in on Black Holes, our April profile of Genzel’s competitor, UCLA astronomer Andrez Ghez.