Hartley Berger, age 13, of Winnipeg, Manitoba, Canada, for his question:
WHAT IS A BLACK HOLE?
Astronomers invented the term black hole to explain something in the vast reaches of outer space. Based on what they know about cosmic laws, there should be certain objects where gravity is so strong that even light cannot escape. After years of patient probing, it now seems likely that such an object has been found and black holes really do exist.
In September we watched a nova, a new star, blaze up and subside in the constellation Cygnus, the Swan. A few years ago, in that same celestial neighborhood, astronomers identified what may prove to be a black hole. This strange object is estimated to be about 5,000 light years from the earth which means that its various X ray signals have traveled 5,000 years to reach us. Cygnus X 1, as the strange object is called, is a binary system, including a large and a small stellar object orbiting around each other.
The small object is extremely dense, and a thimbleful of its tightly packed material weighs many tons. Dense little objects of this sort occur when large stars collapse, perhaps after the stupendous explosion which creates a supernova. However, the small partner in Cygnus X 1 does not qualify as either a white dwarf star or a pulsar.
Other evidence revealed that gaseous material was being drawn from the large star into its small partner. The situation had all the earmarks of a black hole, something that astronomers had believed in for some time.
The theory of the black hole is based on what could happen when a collapsed star continues to collapse to an almost impossible density. Since gravity is related to mass, its gravitational pulling power becomes enormously powerful. Normal earth gravity prevents objects from escaping the surface. The pulling power of a black hole object prevents the escape of electromagnetic radiations including light.
No light, radio or anything else can escape from 'the surface, and a black hole disappears from the universe. However, when other objects come within close range, the gravitational force of the black hole pulls them down intoits bottomless pit. This could explain various X ray signals that come from the binary system. It is thought that these occur when gobs of matter from the large partner are pulled down into the black hole.