Lance Butler, age 13, of Chattanooga, Tenn., for his question:
WHAT IS A BLACK HOLE IN SPACE?
A black hole in space is an invisible object that many astronomers believe actually exists in space. The object has such a strong gravitational force that nothing, not even light, can escape from it.
Some astronomers say that black holes make up as much as a third of the material in the earth's galaxy, the Milky Way.
Many astronomers say that a black hole may form when a large star collapses inward from its own weight. The star is compressed, as it collapses, and its density increases greatly. The extreme density of the collapsed star causes its surface gravitational force to increase tremendously.
As a large star collapses, the force becomes so great that the star's light cannot escape and that's how it becomes invisible.
Astronomers have visualized a collapsed star as a hole in space. The hole may attract and retain nearby orbiting objects including comets and even planets.
Astronomers believe that when a star becomes a black hole, its size decreases. The sun, which is a star, has a diameter of about 865,000 miles. To become a black hole, the sun would have to be compressed to a diameter of less than four miles.
Astronomers have not been able to prove the existence of black holes because the holes are invisible. But they have tried to locate black holes by observing the effect of their gravitational pull on other objects.
During the early 1970s, some astronomers discovered a star that orbited what seemed to be an invisible object in the constellation Cygnus. They feel sure that this object was a black hole.
The Milky Way is a glowing band of starlight from billions of stars within our star system or galaxy. The galaxy is actually shaped like a pancake. But at night, we see it as a milky looking strip of stars because we are inside it. The stars fan out from the center in many wide, curving arms that would give the galaxy the look of a spiral or coil shape if we could get up high enough to see it from above.
Our Milky Way, and the black holes that are probably in it, has a diameter that is about 10 times greater than its thickness.
Big is the only word you can use to describe the size of The Milky Way. It is so big that light, which travels 186,282 miles per second, takes about 100,000 years to travel from one end of it to the other.
Our solar system is only a tiny speck located about 30,000 light years from the center of the galaxy. It is about midway between the upper and lower edges of the galaxy.