Transcript: We’ve discovered a supermassive black hole in the center of our galaxy the Milky Way. However, it would violate the Copernican principle if the Milky Way were unique in any way, so astronomers anticipated black holes in other galaxies or other evidence of nuclear activity. There are two main things that astronomers search for when they are trying to detect a supermassive black hole in another galaxy. The first is a sharp peak or cusp in the light distribution, and the second is a high stellar velocity dispersion. The cusp in the light distribution is measured by imaging, the higher resolution the better, so usually this work is done from space with the Hubble Space Telescope. The spectroscopy is also best done from space where the smallest slit must be placed over the center of the galaxy to isolate the stellar motions in the very central regions. If a galaxy has a cusp in its light distribution and a high degree of stellar motion near the center then the implied mass to light ratio will be higher than any plausible stellar population, so dark, concentrated mass is indicated: a supermassive black hole.