The Mysteries of Black Holes

Black holes have puzzled physicists from the time they were predicted by Newton and Einstein. Pierre La Place of France and John Michell of England studied the possible existence of black holes independently. In 1967 American physicist, John Wheeler used the term 'black hole' for the first time. A black hole is a spot in space that because of the concentration of mass in the area has immense gravitational powers. The escape velocity (or the velocity an object needs to escape from the place) of black holes is greater than the velocity of light. Even though light has very high velocity, it cannot escape from the black hole. It is pulled back by the black hole's greater gravity.

Depending on their masses or size, black holes are grouped into two categories- Stellar black holes range between 1.5 to 14 solar masses and Super Massive black holes equaling millions of solar masses. In addition, there two other categories -Intermediate black holes have around 14 solar masses and the other merely suspected to exist called Micro black holes

Black holes were at first called invisible stars because they cannot be seen. However, scientist can know that there is black hole by studying its effect on the stars close by. When a black hole is created, the gases and dust from a nearby star is attracted to the black hole if it comes closer. They begin to orbit around the horizon or edge of the black hole and eventually orbit into it. A lot of heat is emitted when the dust and gas are compressed while orbiting the horizon. The hot matter is called accretion disk and it is the sign that there is a black hole. The Hubble Space Telescope was fitted with an instrument called Space Telescope Imaging Spectrograph in 1997. The STIS acts as black hole hunter by taking the spectrum of various points in the galaxy simultaneously. The spectrum gives the scientist an idea of how fast the gases and stars are swirling.

Black holes come into existence when massive stars collapse or die. A healthy star can maintain the balance between its gravity pulling in and pressure pulling externally. However, when the star runs out of fuel, the gravity emerges victorious. The core of the star compresses due to the force of gravity and collapses. Not all stars collapse to become black holes. Only stars that are up to twenty times bigger than our sun become black holes. Small stars run out of fuel and die quietly.

Black holes have been conceived as tunnels that can be used to travel to a distant point in the universe by many filmmakers and sci-fi writers. Unfortunately, this is impossible. Once a space ship enters a black hole, the density inside the hole would rip the ship apart.
Black hole evaporates gradually, according to astronomer Stephen Hawking. The phenomenon is called Hawking radiation. If the mass of the black hole is equal to the sun, it could evaporate in 1067 years or even take longer. For now, black holes will continue to mystify us