A spiral-shaped disk of dust fueling a massive black hole in the center of the galaxy NGC 4261. L. Ferrarese (Johns Hopkins University) and NASA.

Black Holes can form from a supernova explosion. The collapse of a star's surface inward causes the explosion. And it also makes a black hole. But only if the star was big enough. It takes a pretty big star to make a Black Hole.

Some astronomers believe that they have seen Black Holes indirectly. They think that they can see Black Holes gobbling up stars that got too close to them. They also think that most galaxies may have a giant Black Holes in their centers.

What would it be like to enter a black hole? Not fun. First, as you approach the black hole the difference in gravity's pull on your head compared to your feet would rip you apart. But suppose you survived that. Once you entered the Black Hole you cannot return, remember not even light gets away from a Black Hole. In the end the Black Hole would crush you out of existence. So I wouldn't try it if I were you.

A spiral-shaped disk of dust fueling a massive black hole in the center of the galaxy NGC 4261. L. Ferrarese (Johns Hopkins University) and NASA.

Black Holes may form as the result of the collapse of a very massive star at its death. Just as neutron stars form during a supernova explosion of a very massive star so do black holes. But in the black hole case the initial star was so massive that nothing could stop its gravitational collapse. All the matter of the star's core is crushed to an infinitely small point, a singularity.

A black hole is sheilded from the outside world by what is called an event horizon. This is a sphere around the black hole where light can no longer escape. Everything that crosses the event horizon is gone forever.

Despite the blackness of black holes there is evidence of their existence. If a black hole forms near a star it may get gobbled up by the black hole. And this can be seen by Astronomers. Some believe that many if not most galaxies harbor suppermassive black holes in their cores. These black holes have gobbled so much matter that they have the mass of billions of suns.

What would it be like to enter a black hole? Not pleasant. First, as you approach the black hole the difference in the gravitaional pull on your head compared to your feet (known as tidal forces) would rip you apart. But suppose you survived that. Once you cross the event horizon there is no turning back. Then the only thing to do is avoid the black hole itself at all costs. If you run into that singularity it will crush your body right out of existence.

If people from Earth were watching your journey into a black hole they would never see you cross the event horizon. Albert Einstein's theory of General Relativity says that as you approach a black hole your time slows down. The closer you get to the black hole the more you appear to be in slow motion as seen by Earth. Eventually you appear to be frozen in time as you cross the event horizon. You would notice nothing different whatsoever. If you were to change your mind right before crossing the event horizon and return to Earth you would find it in the very distant future. You've become a time traveler! Neat huh?

A spiral-shaped disk of dust fueling a massive black hole in the center of the galaxy NGC 4261. L. Ferrarese (Johns Hopkins University) and NASA.

Black Holes may form as the result of the collapse of a very massive star at its death. Just as neutron stars form during a supernova explosion of a very massive star so do black holes. But in the black hole case the initial star was so massive that not even the quantum mechanical pressures that keep neutrons from collapsing can halt the force of gravity's pull. All the matter of the star's core is crushed to an infinitely small point, a singularity.

A black hole is sheilded from the outside world by what is called an event horizon. This is a sphere around the black hole where the escape velocity is the speed of light. Interior to this horizon the escape velocity is greater than light, and since nothing may move faster than light everything that crosses the event horizon is gone forever.

Despite the blackness of black holes there has been evidence of their existence. If a black hole forms near a star it may pull matter from that star's surface off. The matter spirals toward the black hole in an accretion disc. This accretion disc will emit X-rays. Such X-ray sources have been detected and some show evidence that the object accreting the matter is so massive that it must be a Black Hole. Other such methods have led some to believe that many if not most galaxies harber suppermassive black holes in their cores. These black holes have gobbled so much matter that they have the mass of billions of suns.

What would it be like to enter a black hole? None too pleasant. First, as you approach the black hole the difference in the gravitaional pull on your head compared to your feet (known as tidal forces) would literally rip you apart. But suppose you survived that. Once you cross the event horizon there is no turning back and the only thing to do is avoid the black hole itself at all costs. If you run into that singularity it will crush every atom, every proton, neutron, electron, quark, etc. of your body right out of existence.

Interestingly, if people from Earth were observing your decent into a black hole they would never see you cross the event horizon. Albert Einstein's theory of General Relativity says that as you approach a black hole your time slows down. The closer you get to the black hole the more you appear to be in slow motion as seen by Earth observers very far away. Eventually you appear to be frozen in time as you cross the event horizon. Of course, you notice nothing different whatsoever. But if you were to suddenly change your mind right before crossing the event horizon and return to Earth you would find it in the very distant future. You've become a time traveler! Neat huh?