At the very center of our galaxy, something very strange is occurring. We can not see with optical light (too much dust extinction). However, radio emission called synchrotron radiation and produced by high-speed electron, shows some dramatic pictures. Along the direction of the Constellation Sagittarius, there are huge radio plumes, suggesting enormous energy. This region is called Sagittarius A.

Very careful monitoring of the exact position of the bright, radio source, Sgr A* has been kept, relative to very distant objects for more than two decades. Sgr A*'s position NEVER varies. The object is also seen to flare in the infrared. What is Sgr A*?

By looking at the motions of the stars nearby (shown to the left), Astronomers have measured the mass of this unseen object. It appears to have a mass of:

M_SgrA* = 10⁶ M_Sun (a million Suns)

Yet, it lies in an area no bigger than our Solar System. Most astronomers believe it is a million solar mass Black Hole, that sits at the exact center of our Galaxy. For a movie of the orbiting stars, click here

The Halo of our Galaxy

Globular Clusters and other old stars reside in the Halo. They can be found to rotate in any direction, clock-wise, counter-clock-wise. They can have 'cigar-shaped' or very round orbits. Halo stars, because they formed long, long ago, have very few elements beyond H and He in them.

Recently, astronomers have found that our Milky Way galaxy has captured small satellite galaxies, which then reside spread out in the Halo. See here for more on galactic cannibalism.