Galaxies wrap their black holes in loving arms

The thing about black holes is, they're black. That makes them hard to find, of course, but once you find one it's also hard to get any information about it. The only way we can figure out anything about them is by looking at how they affect things around them: how stars orbit them, how material falls in and gives off light, and so on. After observing many galaxies over many decades, it was found that every large galaxy has a supermassive black hole at its core, where supermassive means thousands, millions, or even billions of times the mass of the Sun. The way to weigh a black hole is to carefully measure the velocity of stars in orbit around them; the faster they move, the more massive the black hole. Thanks to Kepler, we can use those measurements to get a decent estimate of the central black hole mass. ...