BLACK HOLES

Black holes are one of the most mysterious and fascinating objects in the universe, ever known to mankind. For decades they have been the objects of extensive study, research and controversy to many. But what exactly are they, and why are they so important?

A black hole is formed when a gigantic star, having a mass more than 3 times our sun’s, reaches the end of its life when it runs out of fuel to burn. This causes it’s exterior to explode into a massive supernova, and it’s interior to implode and compress under the force of its own gravity, into a tiny mass or singularity.

Black holes are the densest objects in the universe. They exert so much gravitational force that not only light, but even space and time cannot escape their pull. Since neither light nor electromagnetic radiation can escape their pull, they appear as ‘black’ holes in space. The boundary of a black hole is called its event horizon.

There are three types of black holes: Miniature Black holes, Supermassive Black holes, and Stellar Black holes. When the big bang occurred 13.7 billion years ago, some parts expanded more rapidly than others, compressing matter into Miniature Black holes. These black holes have event horizons as small as atomic particles and contain considerably less matter than other kinds of black holes.

Supermassive Black holes are the biggest kinds of black holes and are thought to be at the centre of most spiral galaxies, including our own Milky way. Unlike other black holes, they are constantly growing, by pulling in material from galaxies around them. Their size is equal to a hundred thousand solar masses.

Stellar Black holes are formed when massive stars die and collapse under the weight of their own gravity.

One of the most interesting phenomenon about black holes is that since they bend space-time to the point where even light can’t escape; they subsequently cause time to slow down, relative to the outside world. So suppose we are close to the event horizon of a black hole holding a giant clock, and are approaching it slowly, time for us will remain the same but for a person standing at some distance, the clock will appear to tick slower as we come closer to the event horizon.The person standing at some distance will then percieve the clock to have stopped ticking altogether. This is because the mass of an object is inversely proportional to the time  percieved in its close proximity.

This phenomenon is applicable for all objects, even satellites orbitting the earth. For example, the time measured on a satellite's clock will be a billionth of a milisecond faster than the time on the earth, since the satellite will be away from the earth's gravitational pull. Since black holes have such a large mass compared to the earth, they are capable of slowing down time to the point of infinity.

Another controversial feature of black holes are that they emit radiation, known as hawking radiation, after physicist stephen hawking's prediction in 1972. According to his prediction, when a particle and an antiparticle are created near the event horizon of a black hole due to fluctuations in vaccum, one particle will fall into the black hole and one will fall out, before they can annihilate each other. The particle that has fallen out will have positive energy and the particle that has fallen in, will have negative energy. Since the black hole will have lost positive energy, it will have lost some mass as well. So the black hole would continue to lose mass unless it can pull in material from around itself. This is also the reason for the small size and lifespan of a micro or miniature black hole. 

Black holes are thus vast objects of uncertainity, curiosity and mystery for scientists and laymen alike. They shall continue to stir debates and controversies for years to come.