Galaxies seem to grow around supermassive black holes, as we will study in more detail when we discuss active galactic nuclei. There is a supermassive black hole (about 3 million times the mass of the sun) in the center of the Milky Way, and we can study it and its surroundings in far finer detail than we can for the nucleus of any other galaxy. For example, the picture below shows the nearest external galaxy with an "active" central black hole, Centaurus A, and compares an unresolved spot in its nucleus with what we can see in a spot of the same physical size in the Galactic Center.

cenAflsh.gif (150225 bytes) HST images of the center of Centaurus A (from A color optical picture is to the left, while a near infrared image is to the right. The infrared light penetrates the dust and shows the nucleus glowing in light from the supermassive black hole. The small flashing square is an unresolved region about half a parsec in size.
gc_color.jpg (314180 bytes) A region in the center of the Milky Way about half a parsec in size, the same physical size as the unresolved flashing black dot above in Centaurus A. (From Gemini Telescope,