Have you ever watched the whirlpool that is made in your bathtub when the water drains out? A black hole is like a whirlpool in space, dragging any stars that pass close enough to their destruction. Do you know what powers a whirlpool? Gravity does! When a supernova collapses a heavy neutron star is formed. If that same star had been bigger, a smaller, heavier black hole with much more gravity would have been created. Astronomers have been able to prove neutron stars or pulsars exist because they send out radio waves, but a black hole's gravity is so strong it won't even let light escape from it. To be able to find a black hole, astronomers must look for its effect on other objects in the sky. Although X-ray radiation also cannot escape from a black hole, a star that circles it can have its gas pulled away. The radiation generated from the hot gas is transferred into the empty space beside it and this can be measured. Scientists have found the space is very small, but the gravitational pull is incredibly strong, so they believe they are seeing a black hole at work. Where would you look for the nearest black hole? Many of the stars in other galaxies appear to be orbiting around a huge, empty space. Maybe this is also what keeps Earth's Milky Way Galaxy spinning around.