25th May: Black Holes

On this date in 1994, astronomers announced that the Hubble Space Telescope had for the first time confirmed the existence of a black hole. It was found in the constellation Virgo. Here are some facts about black holes.

1. What is a Black hole, anyway? They are objects in space which have a lot of mass compressed into such as small space that their gravitational field is huge. Not even light can escape its pull.
2. This isn't to say they suck like Vacuum cleaners and that one day they'll clean up the universe. They don't do that any more than our own Sun does - they simply have this massive amount of gravity. If our sun became a black hole (which it won't, this is just an illustration so don't panic) the Earth would continue to orbit it exactly as it does now. As long as you don't cross the event horizon they can be observed safely from a distance.
3. Black holes range in size from supermassive black holes which have the mass of millions of suns to primordial black holes which can be as small as an atom. The most common type is the stellar black hole, about 20 times bigger than our sun.
4. Einstein didn't discover black holes, but he did predict them in his Theory of Relativity. It was a man called Karl Schwarzschild who did more work on Einstein's equations and proved they exist. In fact, even before Einstein there were scientists who theorised that there might be such a thing as a black hole, although John Michell and Pierre-Simon Laplace in the 18th century called them "dark stars". "Frozen star" was another term used to describe a star's collapse to the point that light couldn't escape and it would appear frozen in time. John Wheeler coined the term "black hole" as it appeared that they swallowed all the light and gave nothing back.
5. It's not strictly true that they don't emit anything. They do in fact evaporate, gradually dispersing some of their mass into space over time until they disappear. Stephen Hawking figured this out in 1974, so the phenomenon is called "Hawking radiation". For large black holes this happens very slowly, but if you have a very small one it would happen very fast. Scientists at Kansas University have worked out that there is an optimum size for a black hole which is small enough to be artificially created and large enough that it lasts for long enough for us to harness its energy. That's pretty small - about one one-thousandth the size of a proton, but a black hole like that, they say, could be used to power a starship.
6. You cannot see a black hole because it doesn't give off any light. It can't even be seen through instruments using any kind of electromagnetic radiation, like X Rays, for example. The way to spot one is to look at what's happening around it. For example, if a black hole is captured by a black hole its matter gets faster and hotter and that can be detected by X-rays.
7. Strange things happen to time and space around black holes. It gets warped, to the extent that time passes more slowly for someone falling into a black hole than it does for someone watching from a safe distance.
8. The black holes we know about are made from collapsing stars, but in theory, anything could be turned into a black hole if you compress it enough. That's everything from the sun to a human being to your car keys.
9. Black holes could be the ultimate in star recycling centres. As things get pulled into a black hole they get broken down into subatomic particles, which can create elements such as Iron and carbon and others that are essential to the formation of life, and influence the production of new stars. Some scientists think the number of stars in the universe is limited by the number of black holes; without black holes, none of us would exist.
10. Nobody really knows what goes on in the middle of a black hole and so there has been a lot of speculation by science fiction authors. Perhaps they act as wormholes to other parts of the universe, or even other universes. Perhaps the laws of physics don't even apply there, or could be altered sufficiently to create new universes slightly different to our own.

See details of all my books

Browse other topics I've covered in this blog - HERE.

Like my Facebook page for news of Topical Ten posts posts on my writing blog, a weekly writing quote and news of upcoming publications