Introduction to Black Holes

Hello everyone! 

Black Holes. The topic of interest for so many science fiction writers. As Stephen Hawking said at a lecture in Chile, "It is said that fact is sometimes stranger than fiction, and nowhere is this more true than in the case of black holes." NASA (National Aeronautics and Science Administration) says that by definition a black hole is a region where matter collapses to infinite density. Where does it go? How does it work? What happens to the objects absorbed? In todays post, a few of those questions will be answered.

So what are black holes? A black hole is very similar to a vacuum cleaner, the only two differences between a vacuum cleaner and a black hole is that a black hole does not use suction, the force would not be powerful enough and black holes can "suck" infinitely and do not "fill up." Instead of suction, black holes use the force of gravity. A black hole is where gravity has become so strong that nothing around it can escape, not even light. The mass of a black hole is so compact, or dense, that the force of gravity is too strong for even light to escape.

Black holes are truly invisible to the human eye. We can't actually see black holes because they don't reflect light, as that is how the human eye sees objects. Scientists know they exist by observing light and objects around black holes. Strange things happen around black holes to do with quantum physics and space time.

Figure 1: An artist impression of a star being pulled gradually into the black hole.

Black holes are created from dead stars of which the core has collapsed in on itself. In order for a stars core to collapse on itself, the star needs to be massive enough. In figure 1, there are a few possible reasons why a black hole is so near to a star. The first is that it could possibly be a binary solar system, where two stars rotate around each other, and one of them have exploded. The stars would have to have been, initially, further apart, otherwise the other star would have been damaged in the explosion. 
The second explanation is that the stars path has intersected with the black holes and has been caught in its gravitational pull.


There are four parts that make up the anatomy of a black hole; the event horizon, the singularity, the accretion disk and the polar jets. The event horizon has two parts, the inner event horizon and the outer event horizon. Within the Outer Event Horizon you would still be able to escape from a black hole’s gravity because the gravity is not as strong here. If you didn’t escape the black holes gravity before you entered the inner event horizon, then you have missed your chance to escape. The gravity in this layer is much stronger and does not let go of objects it “captures.” At this point you would begin to fall towards the centre of the black hole. 

The singularity is the reason for the strong gravitational "pull" as it is at the centre of the black hole and was originally the stars core. A simple way of thinking of a singularity is as a squashed up star. It is a geometric point in space where mass is compressed to infinite density and zero volume. 
The accretion disk is the ring of space matter surrounding the black hole. This ring rotates around the black hole, just beyond the event horizon but still under the influence of the gravitational "pull" of the black hole.

The polar jets are fountains of energy being thrown from the black hole. The closer matter gets to a supermassive black hole, the more gravity squeezes the matter. As a result, energy spews outward and gets forced into high-speed jets by nearby magnetic fields.

A good way of thinking of a black hole, and how it works, is to think of a whirlpool in the ocean as shown in figure 2. The flow of the water represents the gravitational pull. If you are driving a boat and the whirlpool is in your direct path,  you go around it. If your boat gets caught in the pull, but you haven't yet reached the event horizon, you can still escape. If your boat got caught on the event horizon, it will stay stationary, perfectly balanced, unable to escape, but the force is not strong enough to pull you into it. If you are the unfortunate soul who passes the event horizon, you will be unable to escape, and pulled into the singularity.

Figure 2: How the gravitational pull of a black hole is similar to a whirlpool.

Now, it's your turn. Do the following research questions, the answers of which will be on the next post.

1. What is the nearest black hole to earth?
2. Is there a limit to the size of a black hole?
3. Do black holes get bigger as matter gets pulled in?
4. What is the term used to describe the process by which an object would be stretched and ripped apart by gravitational forces on falling into a black hole?
5. During the above process, what colour would the objects turn?

And now for a little joke. 

Q: Why did the black hole burp after eating Jupiter?

A: Too much gas!

Good Luck, have fun and thanks for visiting. Hang around for the next post for the answers.

Enjoy :)

Emily.