Ever wondered of a place from where no traveler can return? Ever thought if time could slow down?  Let's learn about black holes and unravel the mysteries and questions which surround it.

According to Wikipedia, "A 'black hole' is a region of space-time exhibiting such strong gravitational effects that nothing - including particles and electromagnetic radiation such as light - can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform space-time to form a black hole."

In the 18th century, John Mitchell imagined a star so massive that its gravitational force could pull literally anything. He discovered that if a star is found revolving in an orbit around 'nothing' in space, then there has to be something at the centre which exerts the gravitational pull which causes the star to orbit around it (something similar to what happens between the moons and the planet around which it orbits; but instead of always being in a constant revolution around the black hole, the stars are slowly drawn towards it and ends up getting swallowed), he called these swallowing spaces 'dark stars'. This dark star that Mitchell imagined is what we call today the 'black holes'. Not all stars in the space can become black holes. Only the ones which are massive enough to leave behind it's gravity after it has collapsed, become black holes. The gravitational force is so high that not even light can escape it. It swallows all matters around it. Albert Einstein first predicted black holes in 1915 and supported it with his general theory of relativity.

How is a black hole formed?

At the core of the massive star, nuclear reactions are going on which provide pressure to push outward. As long as the force of gravity and the pressure due to nuclear reactions balance each other, the star remains stable. But when the star runs out of nuclear fuel, the force due to gravity dominates over the pressure to push outward. Hence, the core shrinks due to gravity and the whole star collapses due to its own mass, producing what you call the 'black hole'. All the matter gets squeezed into a smaller space, a space which is of course invisible because even light cannot escape the force of this black hole, which was once a giant star.

How do scientists spot black holes if they are invisible?

Black holes cannot be seen through normal telescopes. Scientists use telescopes equipped with special tools to see these black holes. They spot black holes when they see stars behaving differently in space. They use X-Rays to spot back holes; the disk of gas around the black hole glows brilliantly in X-Rays.

Why is Earth not being swallowed by a black hole?

Black holes do not move around the whole space engulfing all the stars, planets and other space matters. But anything that passes within the boundary of a black hole called the 'event horizon' is trapped forever. Earth is not close enough to any black hole to be eaten up by it. The only star of our solar system i.e., the Sun is not big enough a star to ever become a black hole.

Wow!  Black holes can be portals to new universes.

Stephen Hawking says that he no longer believes that whatever is sucked inside a black hole is completely destroyed, he thinks that black holes could be sending whatever that is sucked in, to other universes or they might be throwing it back to our own universe in different forms. In a lecture at Harvard University, he compared it to a burned encyclopedia, where all the information is still their but cannot be recognized anymore.

Something to ponder upon

If black holes have universes inside it and if the universe inside a black hole has other black holes in it, who knows if our own universe is inside a black hole too?

Did you know?

When a very massive star exhausts its nuclear fuel it explodes as a 'supernova' and throws the outer matter into space, violently.

The first black hole discovered was Cygnus X-1.

Time is said to slow down, once you cross the 'event horizon' and start falling towards the black hole. This is again  in accordance with  Einstein's general theory of relativity which in simple terms says that time is affected by how fast you go, when you are at extreme speed, close to the speed of light.