why do astronomers think that the centers of (most) galaxies contain supermassive black holes?
The most direct evidence is: • A lot of mass (inferred from velocities of stars or gas) • in a small space (inferred from imaging). Supporting evidence is: • Active Galactic Nuclei. Week 11 (Nov 1) History of understanding of our Galaxy, the Milky Way • On Tuesday there was a Fiske Planetarium show on the Milky Way. The show was mostly about the history of the discovery that the Milky Way is a galaxy of stars, and that there are many other galaxies in the Universe. • My favorite book on the subject is Leila Belkora’s “Minding the Heavens: The Story of Our Discovery of the Milky Way” • The ancients had various imaginative ideas about the Milky Way. Our word galaxy comes from Greek galaktikos = milky. • Galileo was the first person to use a telescope in astronomy. He found (1610) that parts of the Milky Way resolved into numerous stars. • Philosopher Kant proposed (1755) that some nebulae were “Island Universes”, comparable to the Milky Way in size, rotating according to Newton’s laws of
