What do black holes eat?
Although a black hole can swallow anything, it is rather hard to feed it compact objects like stars or planets. Black holes mostly eat gas instead. Compact objects simply orbit in, swing around, and continue off in their orbits back away from the black hole. It’s a bit like Halley’s comet coming close to the sun from the outer Solar System every 76 years and then orbiting out. To spiral into the black hole matter needs to slow down to avoid flying off into space again. Gas can do this because viscosity provides friction which slows it down. What is a quasar? A quasar, or as researchers tend to call them, AGNs (for “active galactic nuclei”), are actively accreting black holes in the centers (“nuclei”) of galaxies. Because they are accreting matter they are putting out a lot of energy. The brightest ones far outshine the galaxies in which they are located. Why is so much energy given out when gas spirals into black holes? When friction slows something down it generates heat. If you rub y
