What are Quasars?
In the 1960s, astronomers measured strong radio emissions from faint, star-like points. These were called “quasars” (shortened from “quasi-stellar radio source”) and although they look optically identical to stars, astronomers soon discovered that quasars are moving away from us at high speeds, meaning that they’re actually incredibly far away. They’re also quite small, only about the size of our solar system, and so in order to appear as bright as stars quasars must be emitting enormous amounts of electromagnetic radiation: as much energy per second as a thousand galaxies. The only currently-known event that would produce such a high-energy output is matter interacting with supermassive black holes, which are at the centre of almost all galaxies, including our own. So, quasars are believed to be supermassive black holes at the centres of young galaxies. The energy we see is produced when huge quantities of gas spirals rapidly into the gravitational whirlpool, becoming heated to temperatures of millions of degrees—then part of it escapes as hot wind or superheated beams that shoot away from the black hole’s accretion disk. We’ve observed over 60,000 of them so far, the closest at 780 million light-years away and the furthest at 12 billion, nearer to the birth of the universe than to us. It’s thought that most galaxies have gone through an active stage as a quasar, but are now quiet because they’ve exhausted their supplies of matter to feed their central black hole.
(Image Credit: 1, 2)