Supermassive Black Holes: Their Formation, and Their Prospects as Probes of Relativistic Gravity

The existence of supermassive collapsed objects in the cores of most galaxies poses still-unanswered questions. First, how did they form, and how does their mass depend on the properties of the host galaxy? Second, can observations probe the metric in the strong-field domain, testing whether it indeed agrees with the Kerr geometry predicted by general relativity (and, if so, what the spin is)?