英語聽力：黑洞吞噬—19

We now know this light is produced by the rotating disk of matter, spinning round the edge of the black hole at the heart of the Cygnus A galaxy, waiting to be devoured. It means that against all popular expectations, the brightest sources of light in the universe are actually black holes.

That fundamental fact is one of the great surprises about black holes. By their very name, you would think that black holes would be these dark objects that wouldn't produce any light and that's true if you just have a black hole sitting by itself alone, it doesn't produce any light. But in nature, we have gas spiraling into black holes and that turns out to produce the most efficient sources of light and the brightest sources of light that we know of in the universe.

So here then was the answer to the great quasar mystery. Quasars are nothing less than feeding, super massive black holes. It was exactly what Donald Lyndon-Bell had first predicted.

Behind every quasar is a black hole. And it took a long time for even astronomers to accept this because it's quite a concept that there are these engines out there that fit a variety of different situations and produce some of the most energetic phenomena we see in the universe.

Today, the black hole at the centre of our galaxy is dark.