The universe is full of mysteries and the black hole is the biggest mystery that we know of today. But what is it? Is it something like a tiny cavity in the space so dark that you will get lost forever? Well, answer to that would be both a yes and a no.
Black holes are hard to understand but we will make it easy for you. So let’s start our journey of understanding one of the biggest mysteries of the universe!
A black hole is a hungry beast
It swallows up everything too close, too slow or too small to fight its gravitational force. With every planet, gas, star or bit of mass-consumed, the black hole grows.
The edge of a black hole, its event horizon, is the point of no return. At the event horizon, light is drawn into a black hole, never to escape. And nothing is faster than light.
If you fell into a black hole, it’s not clear how you would die
Will gravity rip you apart and crush you into the black hole’s core? Or will a firewall of energy sizzle you into oblivion? Could some essence of you ever emerge from a black hole? The question of how you would die inside a black hole is one of the biggest debates in physics. Called the firewall paradox, it was posited in March 2012 by a group of theorists including Donald Marolf, Ahmed Almheiri, James Sully and Joseph Polchinski.
Based on the mathematics in Einstein’s general theory of relativity of 1915, you would fall through the event horizon unscathed, then the force of gravity would pull you into a noodle and ultimately cram you into the singularity, the black hole’s infinitely dense core.
But Dr. Polchinski and his team pitted Einstein against quantum theory, which posited that an event horizon is a blazing firewall of energy that would torch your body to smithereens. However, the presence of a firewall would violate the precious principles of relativity, which decreed the existence of black holes. And so physics is stuck.
Black holes can sing
In 2003, an international team led by the X-ray astronomer Andrew Fabian discovered the longest, oldest, lowest note we’ve heard in the universe — a black hole’s song — using NASA’s Chandra X-ray Observatory. The B flat note, 57 octaves below middle C, appeared as sound waves that emanated from explosive events at the edge of a supermassive black hole in the galaxy NGC 1275.
The notes stayed in the galaxy and never reached us, but we couldn’t have heard them anyway. The lowest note the human ear can detect has an oscillation period of one-twentieth of a second. This B flat’s period was 10 million years.
The “songs” of black holes may be responsible for a declining birthrate of stars in the universe. In clusters of galaxies such as Perseus, the home of NGC 1275, the energy these notes carry is thought to keep the gases too hot to condense and form stars.
There is a black hole in every galaxy
Although no black hole is close enough to Earth to pull the planet to its doom, there are so many black holes in the universe that counting them is impossible. Nearly every galaxy — our own Milky Way, as well as the 100 billion or so other galaxies visible from Earth — shows signs of a supermassive black hole in its centre.
Moreover, the bigger a galaxy is, the more massive is its central black hole. Nobody knows why.
Of the billions of stars in the Milky Way, about one in every 1,000 new stars is massive enough to become a black hole. Our sun is not. But a star 25 times heavier is. Stellar-mass black holes result from the death of these stars and can exist anywhere in the galaxy.
A black hole is not forever
Quantum effects suggest that, as Hawking radiation leaks into the universe, a black hole will dissipate, eventually. It would take many times the age of the universe for a black hole to fully evaporate.
Like Einstein, Dr Hawking at first did not believe his own theory. But the numbers were right. Physicists now view his result as the backbone for whatever future theory will bring together gravity and quantum theory.