You are in a spacecraft in outer space. You start hearing all your alert signals going off. Suddenly you notice an unknown object is sucking you in. Guess what? You just got too close to a black hole!
How Can You See Something Thatís Invisible?
I didnít see the black hole, you say? Well thatís exactly my point. A black hole is black and so is the universe. Any light that hits the black hole will be absorbed instead of reflected. The reason we canít see black holes with just plain light is because the black hole "sucks" all of the light in, so there is nothing to reflect from the black hole.
The two main sources of energy astronomers use to detect black holes are gamma rays and x-rays. A gamma ray is a little different from an x-ray because it doesnít shine as far, but it is a little bit more powerful. We use these rays because they can send better images of black holes than regular light can. The scientists make the picture colorful by using a computer. The color in the computers make it so the scientist can see the black hole better, so the scientist can study more about its properties. If the picture was just black and white, you would pretty much see the same thing over and over. If they are different colors you will see a lot of different things.
How Black Holes Are Created
Try to imagine a star ten to twenty times bigger than our Sun. This is how big a star has to be in order for it to eventually become a black hole. Dead stars in space make black holes. The star dies after creating an enormous explosion, which scientists call a supernova. It creates this massive explosion when it runs out of nuclear gas. Think of a gas fireplace in your house. If it burns out, it means it can no longer produce the fuel needed to produce the fire. Well, itís the same thing for a star except a star will shrink to a fraction of its normal size. As the star gets smaller in size it also gets heavier. A smaller star becomes a white dwarf, while a bigger star becomes a neutron star, or a black hole.
Soon the bits and pieces of the star will combine to form the matter known as a black hole. Any planet that passes the black hole will be sucked in because of the black holes incredible gravitational force.
Once you see this horizon it will seem that it is moving slowly, but once you get closer you will see that it is moving very fast. In fact, it is moving at a speed of about 186,000 miles per hour. Thatís the speed of light! The horizon is light bouncing off the gas particles near the black hole.
Astronomers think there might be millions of black holes, but we just canít see them. A black holeís gravitational pull is so strong that not even light can escape it. For example pretend, a speck of dust is a planet and a vacuum is a black hole. The vacuum can suck the dirt from a piece of carpet with ease. A black hole can suck a planet from its orbit with ease just like the vacume and dirt.
In order to escape the gravitational pull of a black hole, you would have to travel faster than the speed of light. Einstein, through his theory of relativity, says that nothing can go faster than the speed of light, so nothing can escape a black hole.
Proving that Black Holes Exist
Astronomers have been able to prove that black holes exist only by observing the effect of a star close to the black hole. A good example of a star being affected by a black hole is the star
Cygnus X-1. When astronomers look through optical telescopes, they see a huge blue star. (An optical telescope uses light mirrors to magnify stars so scientists can see them.) This star revolves around something invisible (which they think is the black hole) every 56 earth days. Since this invisible star is so massive and invisible, scientist think it is a black hole. Also the way that Cygnus X-1 moves makes astronomers believe that the invisible star is at least ten times larger than our sun.
Getting Sucked into a Black Hole
Astronomers have often wondered what happens when something gets sucked into a black hole. Some astronomers believe that when a you travel through a black hole you go through a tunnel called a worm hole where you would be "changed into energy" according to Einstein. Then you come out of a white hole. If a white hole exists, scientists think they are a small body in space that sends out lots of energy. Other astronomers believe a worm hole is a portal to other universes. They say that matter changes going through a black hole and creates its own universe.
There are also astronomers that think that black holes will always be a mystery. No one can record what goes on inside or outside of a black hole. We can try and try but once you go into a black hole you wonít come out.
A small number of black holes have been detected, but we havenít learned any additional information on them. Black holes have many mysteries that may never be solved.
<http://www.cosmology.berkeley.edu/Education/BHfaq.html> Last visited: December, 2001.
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All pictures courtesy of NASA unless otherwise noted