Black Holes

Black holes have always amazed us to the ends. They never fail to bewilder us and plant an intriguing sapling in our brain everytime. Hence, we will be discussing about some facts and mysteries regarding black holes.

What is a black hole ?

This question keeps haunting the mind of most of the astronomers. The preponderance of the astrophile believe in it and it is an outcome of Einstein’s theory of relativity.

A black hole is a region of spacetime where gravity is so strong that nothing- no particle or even electromagnetic radiations such as light- can escape from it.

On the basis of mass and sizes black holes has been divided into four categories:-

 

1.) Stellar black holes 

When a star with a mass range from five to several ten times  the solar masses collapses due to its own gravitational force the stellar black hole is formed. 

 

This is the most abundant type of black hole in the galaxy. Several dozens of stellar black hole may exist within the Milky Way galaxy.

 

Illustration of stellar black hole

2.) Intermediate black holes 

An intermediate black hole is a class of black holes in which mass varies from  10^2 to 10^5 times the mass of our sun.

 

Several intermediate black hole candidates have been discovered in our galaxy and other galaxies.

Illustration of an intermediate black hole

3.) Supermassive  black holes 

These are the largest type of black holes ever found. They are mainly found at the centre of the massive galaxies. These black holes varies from several hundred thousand to a billion times the mass of the sun.

 

In 2019 astronomers were finally able to process the first-ever picture of a supermassive black hole at the centre of Messier 87 galaxy.  

 

Real image of a supermassive black hole at the center 

of Messier 87 galaxy

 

4.) Miniature black holes

 Also known as Micro black holes are the hypothetical tiny black hole for which quantum mechanical effects plays an important role. This hypothesis was suggested by Stephen Hawking back in 1971. Further studies suggest that a micro black hole could be at energies at low as the Tev range, which is available in a particle such as large hadron collider

Illustration of miniature black hole 

 This is the general definition of it but it’s physical meaning is quite complicated.

Welcome all the astrophiles, to the place of no return: a region where the gravitational pull is so strong, not even light can escape it. This is a Black Hole. It’s ok to feel lost here. Even Albert Einstein, whose theory of general relativity made it possible to conceive of such place, thought the concept was too bizarre to exist. But Einstein was wrong, and so, here you are. But fear not, dear astrophiles, your brain has taken millions of years to get here, and it’s ready for this gaze into the darkness. So let’s get started.

“Facts about Black Holes”

“Black holes are not in fact black at all. But glow with heat radiation. The steady emission of heat energy causes the black holes to lose mass and eventually they disappear in a spectacular explosion. A star vanishes into a black hole and then the black hole itself vanishes.”- Hawking Radiation

 

“A Black Hole is a hungry beast”

According to philosophers, a Black Hole swallows up everything too close, too slow or too small to fight it’s gravitational force. With every planet, gas, star or bit of mass consumed, the black hole, never to escape.

“A Black Hole is not forever.”

Quantum effect suggests that, as Hawking Radiation leaks into the universe, a Black Hole will dissipate, eventually. It will take many times the age of the universe for a Black Hole to fully disappear. Like Einstein, Hawking at first did not believe his own theory. But the numbers were right.

 “Astronomers have evidence for black holes in nearly every galaxy in The Universe.”

Although no black hole is close enough to Earth to pull the planet to it’s 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 it’s center. Moreover the bigger the galaxy, the more massive it’s central black hole. Our sun is not. But a star 25 times heavier is. Stellar-mass black holes results from the death of these stars, and can exist anywhere in the galaxy.

“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 2021 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 will pull you into a noddle and ultimately cram you into a singularity, the black hole’s dense core. But Polchinski and his team pitted Einstein’s against the quantum theory, which posited that an event horizon is a blazing fire ball of energy that would torch your body to smithereens. However, the presence of a fire wall would violate the principals of relativity which decreed the existence of black hole and so physics is stuck.

“Black Holes are stellar tombstones.”

On July 2, 1967, a network of satellites recorded an explosion of gamma rays coming from outer space. In retrospect, it was one of the first indication that black holes are real. Today, scientists believe that a gamma ray burst is the final breathe of a dying star and the birth of a stellar-mass black hole. The dramatic transformation starts when a massive star runs out of fuel. As the star begins to collapse, it explodes. The star’s outer layer spew out into space, but the inside implodes, becoming denser and denser, until there is too much matter in too little. The core succumbs to it’s own gravitational pull and collapses into itself, in extreme cases forming a black hole. Theoretically, if you shrank any mass down into a certain amount of space, it could become a black hole.

“Black Hole can gobble  upto 21 billion suns.”

On March 28, 2011, astronomers detected a long gamma ray burst coming from the center of a galaxy 4 billion light years away. This way the first time humans observed what might have been a dormant black hole eating a star. No matter what a black hole eats- a star, a donkey and iPhone- it’s all the same to a black hole. “A black hole has no hair,” the physicist John Archibald Wheeler once said, meaning that a black hole remembers only the mass, spin and charge of it’s dinner. The more a black hole eats, the more it grows. In 2011, scientists discovered one of the biggest black holes ever, more than 300 million light years away. It weighs enough to have gobbled up 21 billion suns. Scientists want to know if the biggest black holes are the result of the two holes merging or one whole eating a lot. But scientists don’t know how they grew so large.

Scientists believe that for black holes to grow that huge just by eating on cosmic stuff is just unlikely. The universe is not old enough so that Black Holes could not get soooooooo big just by eating others.