Black Hole

So, there you stand at home plate, gripping the bat tightly, waiting for the pitch. Here it comes, the pitcher winds up and releases. You keep your eye on the ball, just as you've been taught. When the time is right, you swing, and you connect solidly. As you watch the ball soar higher and higher, towards the fence, you think it's going into orbit.

Instead, it falls into the center fielder's glove. You're out. Want to know why?

Gravity. You see, that ball was traveling about 40 meters per second. Escape velocity for the Earth's gravity is 11100 meters per second. Not even close.

Now, imagine an object that is so dense, it's gravity so strong, that escape velocity is more than 299,792,458 meters per second. That's the speed of light. If Einstein was right and nothing can travel faster than the speed of light, then nothing could reach escape velocity here.

This is a black hole.

Today's scientists believe that a black hole is the end product in the lifecycle of a giant star. If this star is three or four times as massive as our own sun, even after it has exhausted all its fuel, then it can collapse under its own gravity. Just like a crab burying itself at the beach and pulling the sand down over itself, the collapsing star pulls in everything around it as well.

Because this dying star has such huge mass, it becomes too strong for even neutrons to resist. It eventually collapses down to one incredibly dense point, called a singularity. This singularity is surrounded by an event region in which the gravity is so strong that nothing, not even light, can escape.

Anything that crosses a black hole's event horizon is crushed into an incredibly dense singularity. With the addition of each bit of matter consumed by a black hole, its event horizon continues to expand. The only limit to this expansion is the amount of available matter. It is theoretically possible to consume millions or billions of stars.

In fact, some scientists theorize that rotating black holes (also know as Kerr black holes) which contain billions of dead stars lie at the centers of galaxies.

Black holes are still just a theory, but a very good theory. Now that astronomers have acquired evidence that theoretical white dwarfs and neutron stars really exist, the case for black holes has been strengthened. Since not even light can escape a black hole, then it should be invisible. However, the effects of its massive gravity can be detected.

The idea of black holes was first theorized in the late eighteenth century by English geologist John Mitchell and French astronomer Pierre Simon Laplace. At one time, scientists called them "gravitationally collapsed objects." Russian scientists suggested calling them "collapsars," but it wasn't until 1969 when Princeton physicist, John Wheeler coined the term black hole. Black holes have continued to hold public interest and are a popular fixture of science fiction books and movies.