What is a Black Hole?

A black hole is probably the most amazing, but confusing, object in our solar system. You cannot look into a telescope and see a black hole, because they have such a strong gravitational pull that they don't even allow light to escape (hence, they are black), but we are very sure that they exist because of evidence from the Hubble Telescope imaging and Einstein's General Theory of Relativity, although Einstein denied their existence. We can see black holes because they cause objects to orbit around their event horizon, such as dust particles. When we see this, an observer can theorize that there is a black hole in the area. X-ray emissions are also a way to locate a black hole. There is even a theory that at the center of every galaxy there is a black hole, and the black hole is what keeps galaxies together, including our own Milky Way galaxy.

Black holes form when stars die. When the star is alive and burning, the star's heat balances the force of gravity by pushing outward. When a star's fuel is completely consumed, there is no longer enough heat to work against the force of gravity. This is when then star collapses. What becomes of the star is determined by the amount of mass it had when it died. White dwarfs are the products of stars that were approximately the size of the Sun. Stars that had about three times the Sun's mass are compressed into neutron stars. Black holes are formed by stars with a mass greater than three times that of our Sun.

It is believed that black holes are the product of a star that has collapsed under its own gravity, and forms an object with infinite density. This object is the center of a black hole, called the singularity. A singularity has infinitely strong gravitational pull and the curvature of space-time is so severe that space and time actually disappear. All laws of physics are no longer valid at the singularity, including the General Relativity Theory. This is now called quantum gravity, where space and time are broken, and nobody really knows what happens.

Any object that enters a black hole is gone forever. There is no escape. The event horizon of a black hole is the point of no return. After an object passes the event horizon, the pull of gravity is so severe that there is no possible way of escape or any information leaving the black hole, not even light. In fact, if we were to view an object that was heading toward a black hole, the object would look like it were slowing down, and then the moment before it hit the event horizon, the object would disappear. In reality, the object did meet and pass the event horizon, but the light from the object would be sucked in from the black hole as well, so we could not see it. The event horizon is calculated using the Schwartzschild Radius.R=2GM C^2

The escape velocity at the event horizon and beyond exceeds the speed of light (186,000 miles per second), and since Einstein's General Theory of Relativity says that nothing can exceed the speed of light, nothing could ever escape. The event horizon's size is determined by the amount of mass contained in the singularity.

Black holes do not change, so they can be described by only their characteristics of mass and angular momentum. Some say that they could also contain electric charge, but they would also suck up just as much of the opposite charge to make them have a zero charge. There are different types of theories for black holes, and are named after the scientists who founded them. The Swartzschild does not rotate and does not have a charge. Reissner-Nordstroms do not rotate but have a charge. A Kerr black hole rotates but has no charge, and a Kerr-Newman black hole rotates and has a charge. To say that they have a charge would mean that a black hole was disturbed. If this is so, they would give off gravitational waves, which would make the black hole lose energy and again become stationary or unchanging. Einstein said in his Theory of General Relativity that a stationary object could not emit gravitational waves. Gravitational waves actually are disturbances in space-time.

What could be the good that comes from such a destructive force? In theory, if we could have the technology, black holes would be giant trash disposals for the universe. Nuclear waste and other hazardous materials could be eliminating using a black hole. Some actually say that black holes are the key to traveling in time to the future. Since the event horizon would pull you at the speed of light, and time stops at the speed of light and slows the closer you get, time would theoretically slow for you while the earth ages rapidly compared to you. The only thing is that you would have to make sure you had enough velocity to not enter the event horizon. This is the most extreme use of a black hole, but it could also be used as the ultimate weapon. What other object do we know of that could eliminate entire solar systems in milliseconds?

Whatever the uses of a black hole or theories, we know one thing about them. We know that whatever is there, it is one of the most unusual things in our galaxy. Who knows if we could ever actually use them, but we know that they hold some sort of special purpose in our universe.

Works Cited

Baker, Jason. Black Holes: General Information 05/01/2006 .

Black Holes and Beyond 11/16/1995 05/01/2006 .

Bunn, Ted. Black Hole SEP 1995 05/01/2006 .

Introduction to Black Holes 05/01/2006 .