Are there inactive supermassive black holes in the centers of some galaxies?
Yes. Nowadays most supermassive black holes are inactive. The black hole in the center of the Andromeda galaxy and the one in the center of its small companion galaxy called M32, are very quiet. We only know the black holes are there because of their gravitational effect on stars near them. The black hole in the center of the Milky Way is pretty inactive too. So what specific things do I study about supermassive black holes? I am especially interested in the distribution and motions of the gas close to black holes. This gas is called the “broad-line region.” I am also interested in how the energy is produced. How do I study the gas close to black holes? The gas glows because of the intense radiation ionizing hitting it. This produces what we call an “emission-line” spectrum. The spectrum itself tells us about the physical conditions of the gas and about the nature of the radiation hitting it. In 1972 two Russian astronomers, Victor Lyuty and Anatoly Cherepashchuk, demonstrated that as
