The essay is a brief description of black holes. It discusses some of the theories put forth about black holes, the basic concept of black hole, how they are formed and characteristics of a black hole.
The Mysteries of Black Holes
In 1972, a space craft circling Earth found space X-rays coming from a spot called Cygnus X-1. This was the first black hole to ever be discovered. The notion of a black hole was set into motion by Einstein’s theory of Relativity. However Einstein himself did not believe in the concept of a black hole. It was much later in 1784, when John Michell, Rector of Thornhill Church in Yorkshire and great forgotten 18th Century scientist, became intrigued with the idea of escape velocity. Escape velocity is the speed required by an object to overcome the gravitational force of the star or planet in order to escape, vertically up. Michell followed the following line of thought. He knew that gravity depended upon mass and that the speed of light was fast but finite. He then tried to figure out, hypothetically, the mass of the Sun so that light could not escape its own surface. The answer was, five hundred times its current weight. Thus was born the concept of the ‘Dark Star’.
A black hole is not really a hole. It is in fact a huge star that has been into a small ball. A star undergoing a Supernova explosion, experiences a massive gravitational tug at its core. This tug causes the electron and protons to merge and form super dense particles called neutrons. Thus a neutron star is formed. A neutron star resists the ongoing crush of gravity. However if the remnants of the star after supernova weigh more than three times the mass of the sun, even neutrons cannot hold back the inexorable force of gravity. The neutrons are squashed into oblivion. A darkness forms at the star’s heart and moves relentlessly outwards as the stars brilliance is sucked inwards. The gravitational force of this star is so strong that even light cannot escape its surface. Since the black hole allows no light to escape its surface it appears to be invisible or black. It is therefore called a black hole.
A black hole is visible due to its invisibility. In order to make out the existence of a black hole, scientists study the star affected by a black hole. A black hole may suck in material from a nearby star. The falling gas from the star sends out X-rays at the edge of the black hole. These X-rays can then be tracked. Around a super massive black hole in the center of a galaxy the swirling disk is made of not only gas but also stars. The Hubble telescope is fitted with an instrument called the ‘Space Telescope Imaging Spectrograph (STIS). The purpose of this instrument is to rack black holes. The spectrograph takes a spectrum of many places at once across the center of a galaxy. Each spectrum tells scientists how fast the stars and gas are swirling at that location. This information provides useful insight about the central mass. The faster the revolving bodies move, greater the probability that the central mass is a black hole.
On the 4th of March, 2009, BBC featured an issue of the existence of two ‘dancing black holes’. The discovery was made by Todd Boroson and Tod Lauer of the US National Optical Astronomy Observatory. The black holes discovered are about twenty million and one billion times more massive than our Sun. The black holes are separated by an estimated distance of less than a third of a light year. This distance is almost very close for any black holes discovered till date. Hence the title of the issue – The Dancing (cheek to cheek) Black Holes.
We have indeed come a long way from the theory of relativity in 1916. Einstein did not know what to do with the idea of a lack hole. His successors sure do. Discoveries and experiments continue to unravel the mystery of black holes. The one in march,2009 was the latest, but it can be said without doubt, that there is a lot more to come from the mysterious – ‘Black Holes’.
Smith, Dr. Richard (2000).Black holes – The Ultimate Abyss
Daly, Kathleen N (1982). Question and Answer book (pp 39-40)