A Simple Look at Black Holes and Their Affect on Light and Mass Including Hawking Radiation

So what is a black hole? A good way to look at what a black hole is, is to think of a region of space that has so much mass that everything around it is unable to escape its gravitational pull.

The mass of a planet determines how much gravity that planet has, the higher the mass the greater the gravity and the faster you must fly to reach a speed to get away from the planet. If the mass is so great that light cannot reach the speed to escape it then this mass is called a black hole. The speed to escape an objects mass is called the escape velocity.

Black hole

It is impossible to tell that black holes exist for sure but good old Einstein and his theory of general relativity ofshows us that when a star of sufficient mass collapses a black hole is formed. The effects of black holes have been seen and the predictions of Einstein agree with the observations. This doesn’t mean that that there aren’t other theories are about what a black could be.

A gravastar is an objects that tries to include string theory with a bit of black hole theory to improve and bring up-to-date the basic black hole theory. This theory introduces the idea that black holes aren’t black holes at all but are black bubbles with very thick skins. They are still things that you wouldn’t like to stroll close to.

A dark energy star is another theory and as you might imagine involves dark energy. This theory follows the idea that matter that is falling in is converted into vacuum energy or dark energy. Once again it is impossible to enjoy a visit to a dark energy Star and a clear berth is recommended.

Could this be a black hole?

So gravity can give us an escape velocity that is higher than the speed of light (this means that light cannot escape from a black hole and this point where light is trapped is called the event horizon). If we were looking at a black hole the light from the black hole would not reach us. So what does that mean?

If you crossed the event horizon and a person watched you doing this from a safe distance it would look like you moved slower and slower as you got closer and closer to the event horizon. The person watching you would see that you never actually arrived at the event horizon but this would be an illusion because of the light taking longer and longer to reach the Observer. When you crossed the event horizon nothing special would happen except eventually you would get crushed by the black hole as there is no escape!

Black holes emit matter because their gravity fields are so intense. Black holes release particles by a process known as Hawking radiation. Unfortunately a little bit of weird theory is needed to explain this.

Ordinary space is full of virtual pairs which are particle/antiparticle pairs which pop into existence every now and then. When they appear they separate a very short distance and then get back together and disappear in an extremely short time. The poor old universe doesn’t notice this is happening so the extra mass energy goes unnoticed. The law of conservation of energy only applies over a large period of time and therefore it doesn’t notice this quirk happening.

Near a black the virtual pair can pop into existence and when they separate one can go so deeply into the black hole that it’s falling releases energy (a lot of energy) so that the other particle can continue to exist outside the hole. This release of energy is known as Hawking radiation.

When black holes get rid of all this Hawking radiation you would imagine that they would shrink until they popped out of existence. You would be right! Einstein told us that mass is equal to energy. As losing Hawking radiation is losing energy the mass of a black hole will decrease and eventually cease to exist. Don’t worry though, only the very smallest black holes have had time to evaporate from the universe over the entire 14 billion years the universe has been around, there is still time to take a tour and see the sights.

Black holes are luminous as well. Now that does sound daft after saying that they are black holes. The story goes like this. As the matter falls into the black hole and before it enters the event horizon it turns gravitational potential energy into kinetic energy, this means that the matter has a lot of speed. Some of this energy is converted into light and other electromagnetic energy and makes the black hole luminous.

That was a quick look at light and matter including Hawking radiation from black holes just to add some oddness to your day. Let’s hope one day that we can take a ship and fly around a black hole pointing out these phenomena for our science lesson.

[podcast]http://www.weirdwarp.com/wp-content/uploads/2010/01/Black holes podcast.mp3[/podcast]

Everything you need to know about black holes podcast from universe today.

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