Supermassive Black Hole

Black holes that contain between a million and a billion times more mass than a typical stellar black hole. There are only a handful of confirmed supermassive black holes (most are too far away to be observed), but they probably exist at the centers of most large galaxies, including the center of our Milky Way. For many years there was only indirect evidence of supermassive black holes: the existence of quasars. Observations of the energy output and variability timescales revealed that quasars radiate >1012  times more energy as our Sun from a region about the size of the Solar System. The only mechanism capable of producing such enormous amounts of energy is the conversion of gravitational energy into light by a massive black hole. More recently, direct evidence for supermassive black holes has come from observations of material orbiting galactic centers. High orbital velocities of stars and gas are best explained if they are being accelerated by a massive object with a strong gravitational field contained within a small region of space – a supermassive black hole (below).


Image source: http://astronomy.swin.edu.au/cosmos/C/Centre+Of+The+Milky+Way.

There is still debate about how supermassive black holes form. Supermassive black holes could form from the collapse of massive clouds of gas during the early stages of the formation of the galaxy. Alternatively, a stellar black hole might consume sufficient of material over millions of years to grow into a supermassive black hole proportions. Yet another idea is that a cluster of stellar black holes might merge to form a supermassive black hole. Regardless of the mechanism, most astronomers agree that accretion of material onto a supermassive black hole drives both active galactic nuclei and galactic jets (below).


Bullets in M87 jet. Image source: http://apod.nasa.gov/apod/ap000706.html.