Black Holes

The term “Black Hole” is of very recent origin coined by John Wheeler, an American scientist.

The graphical description and idea of “A BLACK HOLE” goes back to two hundred years when there were two prevalent and widely accepted theories about light. Light was considered to possess two forms (or natures) namely particle and wave nature. The particle nature of light was favored by Newton.

According to the wave nature, light behaves as a wave. The question that arises is that – Can gravity affect light ? Yes, gravity can affect light if it is considered to behave as particle. Roemer discovered that light has a finite speed, therefore, gravity must have important effect on it.

Gravity is seen to have effect on cricket balls, humans and rockets etc. But light is composed of photons. Photon is a particle which can move upwards constantly against gravity without showing retarding effect. How can then Newtonian gravity affect light?

A star is formed when a light amount of hydrogen starts to collapse on itself due to strong gravitational pull. Eventually due to gravity and increasing pressure the gases heat up and finally hydrogen atoms collide to form helium. The heat released in the process makes the star shine.

Oppenheimer’s work was based on black holes.

He proposed that gravitational field of the star changes the path of light rays it emits in space-time. The light cones are bent slightly inwards near the surface of star. As the star passes its years of life, it contracts and its gravitational field becomes stronger and stronger and finally a time comes when the light cones bend inwards so much that it can no longer escape. This results into nothing but a region in universe which is called a black hole.

The boundary of a black hole is called event horizon. It coincides with the path of light rays that just fail to escape from the black hole.