ESCAPE VELOCITY AND THE SIZE OF BLAC HOLE

The process of formation of stars and their evolution will be discussed in some detail in part 2 of the book. Here, we will use the concept of escape velocity to calculate some features of black hole.

In very massive stars (m greater than 3 solar masses) the gravity may become so strong that even light emitted from its surface will not escape and will be pooled back by the gravitational force. In other words escape velocity from such a star is greater than the speed of light in vacuum. Light or radiation of any kinds does not escape from such stars. Nobody can observe it directly. It is completely black, hence the name” black hole” The existence of black hole is inferred by depletion suffered by another body. Any body includes light, coming close enough is swallowed by the black hole. It is suggested that there is a giant black hole at the center of our Milky Way galaxies and its mass is several million times the solar mass. Many galaxies may have black hole at their center.

SATELLITE

A body circling a planet is called satellite. Moon is a natural satellite of the earth. A man made satellite is also called an artificial satellite.

APPLICATION OF ARTIFICIAL SATELLITE

Artificial satellites have found a wide variety of application. Some of them are listed below:

1)   They are used for scientific investigation on the condition in the upper atmosphere, weather study, ecology, remote sensing etc.

2)   They are used for taking photographs of vital installation for intelligence gathering activities.

3)   They are used to study the radiation coming from outer space and from out space and for intelligence gathering activities.

4)   Geostationary satellite are used mostly for communication, transmit TV programs from one part of the world to another, internet and electronic communication.