Some galaxies have extremely luminous nuclei, often outshining the rest of the galaxy.
These objects are called active galactic nuclei . The Milky Way appears to have such an active nucleus. Some active galaxies, like our Milky Way, appear to be powered by supermassive black holes at the center. Other types of active galaxies show evidence of widespread star formation in the inner hundreds of parsecs. Some of these star-forming galaxies, called starbursts , can also be very luminous from large numbers of O and B stars and H II regions.