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Q. What is a black hole? What would happen if I went into one? — Joan P.
A. It's something so dense even light is trapped inside.
A black hole is a tiny little place in space with so much mass concentrated in it that there is no way for anything nearby to escape the pull of its gravity.

Imagine something with such an enormous mass in such a small radius that to escape from it, you would have to travel faster than the speed of light. But, Einstein's general theory of relativity holds that nothing can go faster than light. That means nothing can escape the black hole's gravity. Even the beam from your flashlight would be pulled back by gravity and would be unable to escape.

How does such a beast come to exist? Astronomers say that, when a massive star runs out of fuel and is unable to support itself against its own gravitational pull, it collapses into itself and becomes a black hole.

Interestingly, such humongous objects distort space and time, so the usual rules of geometry don't apply there. A black hole is a sphere with an outer edge called an "event horizon." The tiny little object at the center of the sphere is called a "singularity."

You could pass inward through the event horizon, but you couldn't get back out. In fact, once you crossed the event horizon, you would be doomed to move ever closer to the singularity at the center of the black hole.

Outside of the event horizon, the escape velocity would be less than the speed of light, so if you were to fire your rockets hard enough, you could give yourself enough energy to get away. But if you were to find yourself inside the event horizon, no matter how powerful your rockets might be, you could not escape.

John Archibald Wheeler came up with the catchy name black hole. Before Wheeler, they were referred to as frozen stars.

More black hole stories »»
What is a white hole? It's the opposite of a black hole. Since a black hole is a place from which nothing can escape, a white hole is a place into which nothing can enter. A black hole can only draw things in and a white hole can only push things out. Astronomers say white holes probably don't exist, since there would be no way to produce one. Creating a white hole would seem to be as impossible as destroying a black hole.

What is a wormhole? As if a black hole isn't an odd enough thing in itself, a wormhole is an odd black hole.

Suppose a black hole were to rotate and have an electrical charge. That should make it possible to fall into the black hole, but not hit the singularity at the center. The interior of the charged rotating black hole might meet a corresponding white hole in such a way that something which fell into the black hole would be popped out of the white hole. Such a combination of black and white holes would be a wormhole.

Science fiction writers usually describe white holes as being somewhere far away. For instance, they might be in a place completely disconnected from our own place in the Universe. The sci-fi writers suggest that a conveniently-located wormhole would provide a convenient way to travel large distances quickly. A few even envision an exit from a wormhole in a past time, enabling travel back in time.

Those are mere visions, astronomers say. They suggest wormholes probably don't exist .After all, black holes form from the collapse of ordinary matter. At least, all of the black holes that we think exist seemed to have been formed that way. Wormholes don't form, astronomers say. If something fell into one of the known black holes, it wouldn't miss the center and pop out anywhere. Instead, it would hit the singularity and end.

Even if a wormhole were to form, it probably could not be stable. Any disruption caused by an attempt to travel through it would cause it to collapse.

Even if a wormhole were stable, it probably would make for an unpleasant trip. All sorts of powerful electromagnetic radiation would pour into the wormhole from nearby stars and galaxies. A person traveling through a wormhole surely would be burned to a crisp by x-rays, gamma rays and other kinds of energy.

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