Story of the Unseen Hole and its Mysteries!

“Exploring The Black Hole”

We often say that if certain things are invisible to us that does not necessarily mean they simply don’t exist! They do and such things uniquely interact with us. Like air interacts and proves its existence by enabling us to breathe, by swaying the trees and similarly a black hole.

Among all of the aspects, one is particularly the most liked by scientific minds and they are always searching for new results and theories related to it. It’s none other than the unseen hole – The Black Hole! A body with intense gravitational field that even light can escape, which is the fastest !

Black holes have been a long favorite topic of research. As the more, we learn about it, the more it becomes interesting. But why do we need to study the black holes? How does it affect us? Let’s learn all about this on the journey of exploring Black holes!

Discovery and Predictions: Birth of the idea !

Black holes can be detected by only observing their interaction with other matter and electromagnetic radiation. Owing to its enormous gravitational field, everything in close vicinity eventually falls into it and nothing can escape from it, not even light!

John Michell proposed that a massive star would collapse and form a body so compact that it would have a strong gravitational field that even light could not escape. He suggested that there are a lot of such stars. But we will be unable to see them because their light wouldn’t reach us, but we would still feel their gravitational attraction. Michell termed such bodies ‘Dark stars’! Which we now call ‘Black Holes’.

This idea was accepted widely but eventually faded away due to the new idea of light being a ‘wave’ aroused in the nineteenth century. Physicists back then did not yet know how the light ‘waves’ would interact with gravitational fields or are they were even affected by gravity. This remained a crazy theory until Einstein proposed general relativity.

How are Black Holes formed?

To understand how black holes work, we need to first learn how some stars turn into black holes whereas some are destined for a different fate. So let’s look into the ‘Life Cycle of Stars’ or ‘Fate of Stars’!

Stars are formed within enormous cold, dense clouds of cosmic dust and gas(which mostly consists of Hydrogen). The process of star birth is triggered when the cloud is disturbed either by collision with other interstellar clouds or by a shockwave from a supernova explosion. Gradually the cloud collapses due to its gravitational attraction. As the cloud contracts, the atoms of gas collide with each other at higher speeds, heating the gas!

A protostar is formed! It is the baby stage of a star, where gravity pulls all the material into a core, where the density, pressure and temperature build-up. Eventually, the gas becomes so hot that when the hydrogen atoms collide, they no longer bounce off instead they coalesce to form Helium. This reaction acts like an uncontrolled Hydrogen Bomb! The energy released in these nuclear fusion reactions is enormous, making the star shine. A star is born! 

Star in its Stable stage but not for long

 Star now passes through its stable stage and shines steadily, where the radiation pressure of the nuclear fusion in the core, which expands it outwards, is balanced by the inward push due to the gravitational attraction.

The star stays stable for a long time. Eventually, the star runs out of its fuel and no longer instigates nuclear reactions. The core of the star runs out of hydrogen and fuses to heavier and heavier elements gradually turning the core into iron. The star grows into giant until nuclear reactions are possible and then collapses onto itself due to the gravitational attraction as there is no longer the nuclear force present to keep it stable. Eventually dying with an explosion!

Paradoxically, the more fuel a star starts with, the sooner it runs out of fuel. This is because the more massive the star is, the more fuel it uses, the hotter it needs to be to balance the gravitational attraction. Due to this tremendous heat, the hydrogen in the core of massive stars fuses to heavier elements rapidly! Eventually running out of fuel. But that’s not the case that leads to the formation of black holes. This was just a clear picture of how stars form and evolve.

Only specific stars turn into a Blackhole!

Now, there are different sizes of stars that are born -small, medium and massive. 

We just looked at how sizes determine the lifetime of a star. Massive stars are what we will be focusing on!

The Massive stars run out of fuel quickly and are so massive that they explode while collapsing onto their core. This explosion is what is called a Supernova! After the explosion, the massive core continues to collapse onto itself. What happens next depends on how massive the core is. A relatively smaller core becomes a ‘Neutron Star’ but a massive core of a supermassive star never stops collapsing. It shrinks until its core turns to the size of an atom and becomes a ‘Black Hole’.

There is one more way that gives birth to a black hole and that is when two neutron stars collide. Neutron stars are a very interesting topic to learn about but let’s save it for another article. Let’s focus on Black holes.

Scientists and their love for Black holes

John Michelle’s theory paved the way for greater discoveries related to the cosmological importance of Blackhole.

With the revolutionary general relativity theory proposed by Einstein, the whole of modern physics evolved from the Newtonian era of classical physics. General relativity is the geometrical theory of gravitation showing how matter and massive objects shape the fabric of spacetime and the gravitational attraction between bodies results due to the wrapping of space. 

General relativity predicts the presence of a singularity at the centre of a black hole where the densities and gravitational fields become infinite. For a non-rotating black hole, this region takes the shape of a single point and for a rotating black hole, it is in the form of a ring singularity that lies in the plane of rotation. 

Now when we are looking at a Blackhole we would be looking at its event horizon- the boundary in spacetime through which matter and light only pass inwards. The event that occurred at the horizon and the information from that event cannot reach an outside observer, making it impossible to determine whether such an event occurred. 

This gave rise to the Blackhole information paradox. We know that things that enter the black hole are destroyed along with their Quantum Information. But what if the information is just out of sight and still exists within the void of the hole. Some theories suggest that the information doesn’t even make it in the black hole, it seems as if the information of that object gets encoded on the event horizon of the black hole. So, it is considered possible that when a black hole swallows information it also grows in size to conserve that object’s Quantum information. But either way, the laws of classical physics remain unchanged. 

All the Information leading to major theories

Another major theory accounts for The Hawking radiation! This theory says that Black holes are gradually evaporating, very very slowly! Black holes lose mass as they shed particles away in the form of radiation. Does that mean all the information encoded on the event horizon can be completely erased? This remains unanswered as we haven’t yet figured out what exactly the evaporating contents contain. This also links to the principle of Holographic projection! 

All of these makes the current theories stronger and helps to deduce new ones. But why exactly are black holes so important? Apart from scientific interests and theories, Black holes and their linked theories help us get a clear picture of the universe and help in providing many theories leading towards one “ Unified Theory of Everything !” 

How the formation of Black Holes made life take hold?

The formation of Black holes is out of instability in the star, which eventually undergoes Supernova. Until the core completely collapses, the elements in the core fuse into heavier elements in large numbers. And there is a point when it is not possible further. Eventually, the star collapses and explodes into a supernova. Throwing all the heavier elements like iron, copper, carbon, oxygen, gold, silver, calcium, nitrogen etc.

All these elements combine and meet at a place. They undergo various chemical reactions and form various further compounds. They give rise to something wonderful like the single-celled based organism that first inhaled the oxygen in the earth’s atmosphere, brought to us from millions of lightyears away. Which then evolved into much other carbon-based life, including us! 

There are many more theories related to black holes, one article falls short for that! Till then be Curious and Explore your knowledge.

Always remember “Curiosity is the essence of our Existence.”

Gene Cernan.

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