Cosmology

What do we know about black hole ?

In the depth of the universe and the heart of the galaxies lie mathematical but mysterious regions called ‘BLACK HOLES’ which are supposedly a doorways to parallel or multi-universe that allows us to travel to the very remote places of the universe. Black hole or dark star was first proposed by  John Michell in 1784 . He was natural philosopher and English clergyman .These are the theoretical constructs, equivalent to tunnels or shortcuts, between distinct points in time or space or maybe even in parallel universe. Black holes are so destructive and their interiors are so infinitely dense that they exert massively destructive, ‘tide-like’ distortions on approaching subjects, ripping them into their constituent subatomic particles. They exhibit a very strong gravitational pull, which results in a effect that nothing, not even particles or electromagnetic radiations such as light, can escape from inside it. These horrible black holes drag passers-by to close.

John A. Wheeler at Princeton University Image credit : NY Times

Term ‘BLACK HOLE’ was coined by the quantum physicist
JOHN WHEELER’ in 1967. He spent decades, demonstrating that black holes really were consist with Einstein’s ideas of General relativity and working on how they behave. A common black hole came into existence with a dying
star. A star which has a mass of about 20 times greater than the Sun may produce a black hole at its end.
Throughout the normal life of a star, there is a tug of war between gravity pulling in and pressure pushing out. But,
towards its end, when the nuclear reaction (Conversion of Hydrogen into Helium) is going to stop and fuel
(Hydrogen) is about to end from the perspective of a Einstein’s ideas of General relativity and working on how
they behave. A common black hole came into existence with a dying
star. A star which has a mass of about 20 times greater than the Sun may produce a black hole at its end. Throughout the normal life of a star, there is a tug of war
between gravity pulling in and pressure pushing out. But, towards its end, when the nuclear reaction (Conversion
of Hydrogen into Helium) is going to stop and fuel (Hydrogen) is about to end from the perspective of a collapsing star, it starts compacting into a mathematical
Einstein’s ideas of General relativity and working on how they behave.
A common black hole came into existence with a dying star. A star which has a mass of about 20 times greater
than the Sun may produce a black hole at its end. Throughout the normal life of a star, there is a tug of war between gravity pulling in and pressure pushing out. But, towards its end, when the nuclear reaction (Conversion
of Hydrogen into Helium) is going to stop and fuel (Hydrogen) is about to end from the perspective of a collapsing star, it starts compacting into a mathematical point with virtually zero volume, which is infinitely dense and this is called the Singularity of the Black Holes.

There is a NO HAIR THEOREM which states that, once a black hole achieves a stable condition after formation, it has only three physical properties:

  1. Mass
  2. Electric charge
  3. Angular Momentum.

Type of Black Hole :

Depending on mass of black holes , they are categorised into three parts .

1: Stellar( Stellar -Mass – Black -Hole ) :

They are baby black holes newly formed by the gravitational collapse of a massive star. They have a mass from 5
to several tens of solar masses. They are also known as collapsars .

2. Intermediate-mass black hole (IMBH):

An intermediate-mass black hole is a hypothetical class of black hole with a mass range of 100 to one million solar masses. Basically, they are bigger than a stellar-mass black hole and smaller than a supermassive black hole. The strongest evidence for IMBHs comes from a few low-luminosity active galactic nuclei .

3. Supermassive black holes:

These are the largest and the most dangerous ones in the cosmos, mainly found in the middle of the massive galaxies. They are formed by the collision of many small black holes. As more matter falls into them, they become larger and larger over time. They have a mass greater than millions and billion that of sun.

We also have a Supermassive black hole in the middle of our milky way galaxy, named- ‘Sagittarius A*’ which has
a mass 4 million times greater than that of the Sun.

What would happen when body falls in black hole –

If an object tries to travel through a black hole, it has to go across its four main parts which are Accretion Disk, Outer Event Horizon, Inner Event Horizon and Singularity. Accretion disk is a disk of matter under the influence of gravitational pull of the black hole, which keeps revolving around it because of its angular momentum at a speed       equivalent to the light. An extra force called Centrifugal force also acts on the approaching object due to which there is a fight between the gravity and the centrifugal force. Gravity tries to crush while centrifugal force tries to throw everything outwards. And by getting closer to the accretion disk, time slows down rapidly.

After accretion disk, the object reaches the outer event horizon, where the time and space constantly intermits and the rules of physics works no more. Then a Redshift occurs, following which the object becomes invisible for outsiders who are watching from the Earth. Now, a process called Spaghettification takes place as an effect of tidal gravitational forces. When an object reaches the outer event horizon and the body of the
object gets stretched out until ripped apart due to tidal
gravitational forces, this is called Spaghettification.

Spaghettification. Image credit : Me.Me

Next is Inner Event Horizon which is the most violent place in the universe. Here the matter collapses at a speed greater than that of light. It is a place in the whole universe where the energy is found equivalent to the energy of the ‘BIG BANG’. It is being speculated that there is a baby universe in the emergence in Inner Event horizon . If the object survives these three layers, then it reaches
to the center of the black hole that is ‘SINGULARITY’.

Singularity is a very quiet and dense part of the Black Hole, just like an eye of a tornado. Here spacetime curvature
becomes infinite. This singular region has zero volume. It
is end of a black hole. Till the date, no findings have come
to knowledge which states about the next to Singularity.
It is believed to be the end of Human Mind’s imagination,
the end of time and space.. it is the end of everything….

Conclusion: The black holes are one of the many things in the universe about which the most of the scientist still have a muddy thought. But it is believed that they might prove to be a pathway to lead us to Warmholes through which future time travel could be possible.

Shreya Vashistha

She is student and study in India . She loves space science and want to pursue higher studies in astronomy field . She loves to read science books and watch various space documentary in her free time . She wants to share her knowledge through this website .

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Shreya Vashistha
She is student and study in India . She loves space science and want to pursue higher studies in astronomy field . She loves to read science books and watch various space documentary in her free time . She wants to share her knowledge through this website .