What are quasars?
We think there are supermassive black holes at the centre of every massive galaxy in the Universe. These black holes are accreting material from their near surroundings, usually gas or dust. In some cases, the powerful gravitational forces involved serve to heat up this material, resulting in intense radiation being emitted. We call these extreme objects active galactic nuclei, and quasars are the brightest and most powerful examples of them.
What makes them such mysterious objects?
Supermassive black holes are roughly the size of a solar system. This is very small relative to a full galaxy, which could contain hundreds of millions to trillions of stars. There's lots of gas in galaxies, but the mystery lies in how this can get down to the central black hole regions to provide fuel for a quasar. One of the leading ideas is that when galaxies collide, the net effect is to throw a large amount of material towards the galactic centres, an attractive means of getting fuel to the black hole.
How do astronomers study quasars?
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