𝐁𝐋𝐀𝐂𝐊 𝐇𝐎𝐋𝐄

HELLO EVERYONE👋

My name is Manish kumar. I am  from Gaya Bihar. I am currently pursuing BTech in electronics and communication engineering branch.I am here today to share about 𝐰𝐡𝐚𝐭 𝐢𝐬 𝐛𝐥𝐚𝐜𝐤 𝐡𝐨𝐥𝐞? 𝐇𝐨𝐰 𝐜𝐚𝐧 𝐲𝐨𝐮 𝐮𝐧𝐝𝐞𝐫𝐬𝐭𝐚𝐧𝐝 𝐢𝐭?

The whole concept of blackholes itself is both complex and interesting too.

To get a basic but proper understanding of blackholes, I will explain it step-by-step. Read this post till the end, I swear it's gonna be interesting and gonna clear a lot of concepts.

Let us see the life cycle of supermassive stars, whose core itself is 4 times of our sun

Stars of universe keep on burning, because of the nuclear fission

Stars exist because of a fragile balance. The Trillions of tons of plasma are being pulled inwards by gravity and squeeze material together with so much force that nuclei fuse(hydrogen fuses to helium). This releases energy and pushes against gravity and tries to escape. This is known as hydrostatic equilibrium

As long as this balance exists, stars are pretty stable. Eventually, when the hydrogen gets exhausted, the stars will come into a giant phase, where they burn carbon into oxygen, and then turn into white dwarf. This is what happens to stars like sun. They die out in a thermonuclear explosion

But, in massive stars, when they run out of hydrogen, things get interesting.

For a moment, the balance of pressure and radiation tips, and gravity wins, squeezing the star tighter than before. The core burns hotter and faster, while the outer layers of the star swell by hundreds of times, fusing heavier and heavier elements. Carbon burns to neon in centuries, neon to oxygen in a year, oxygen to silicon in months, and silicon to iron in a day. And then, they implode quarter the speed of light, crushing all the matter into the core.

They explode in a supernova then.

If the mass of the exploded star's core is 4 solar masses or more, then a there would form a region of spacetime where the gravitational field would be so intense that nothing, including electromagnetic radiation like light can escape from. This region is calledBlack hole

Let's now take a step back and look at the relativity.

After Einstein's General Relativity was out, our perspective of gravity has changed. Gravity was earlier viewed as a force.

Space and time, according to relativity, aren't different entities but the same entity called spacetime. The space and time clubbed together is spacetime just like electricity and magnetism clubbed together is electromagnetism.

Space and time are equivalent.

For understanding the concept of blackholes, we need to use the Einsteinian interpretation of gravity rather than the Newtonian one. And this too, I will keep it simple because I don't want to extend to topic.

Take the spacetime as a flexible rubber sheet spread across the whole universe.

That curvature formed is the gravitational field of that object.

If you put an object near the pit formed, it falls towards the object. That's how the gravity concept works according to Einstein's relativity (note - this is just an oversimplification of the much complicated

Einsteinian gravity).

More massive and dense an object is, the more the curvature of spacetime is.

Coming back to the topic.

Blackholes, are like trapdoors in this fabric of spacetime. The curvature of space and time they create is insane.

You can see that the blackholes curvature is very sharp.

A blackhole, can be defined as a region in spacetime where the spacetime is so warped that even light

can't escape from.

Blackholes are formed when lot of mass is crammed into a really small area. Once lot of mass is crammed into required space, the object collapses into a blackhole.

The density limit after which an object collapses into blackhole is called the Schwarzschild Radius of that object.

The formula for Schwarzschild Radius is -

Rs= 2GM/c^2

According to this equation, an object as massive as the Sun needs to be collapsed into 3KM to become a blackhole.

That means, blackholes are really dense. A blackhole of radius of mere 3KM will be as massive as our sun.

Most blackholes in the universe are formed after a supermassive star whose core has a mass 4 times that of our sun, collapses.

While collapsing, the star implodes, compressing the matter in it. The pressure it exerts on its core is so high that the core reaches its Schwarzschild Radius. And then it becomes the blackhole! I have described this previously.

This is how most(not all) blackholes form

Types of blackholes -

. Stellar Blackholes - These blackholes were the ones I have described previously. They are formed after the death of the stars. These blackholes are aren't that big in size, but have a lot of mass.

• Supermassive blackholes - These blackholes are the biggest objects in this universe. Their mass is billions of times that of our sun. They rest in the centre of galaxies. The radius of supermassive blackholes is more than entire star systems.

Besides this, there are other types of blackholes which form from the collision of neutron stars.

The event horizon of a blackhole -

The event horizon of a blackhole, is the point of no return. It is the boundary which separates the events inside the blackhole from the other points in this universe.

Once you cross the event horizon of a blackhole, you need to travel faster than the speed of light to escape. And light speed travel is impossible. Thus, event horizon is a point of no return.

The singularity of a blackhole -

The singularity is like the centre of mass of a blackhole. It is the place where the whole mass of the blackhole, be it 1 billion or million solar masses, is concentrated.

After entering the blackhole, the singularity becomes a point in the infinite future rather than a point in space.

Most blackholes in the universe are rotating. So hence even the singularity too in most blackhole rotates, and is much interesting.

The singularity becomes the ringularity in such blackholes.

Hawking Radiation:-

This topic needs a separate answer itself. I can't explain it here and now. It would create confusion.

The hawking radiation is the radiation through which the blackhole loses its mass, and slowly evaporates.

Observation of blackholes-

We can't see blackholes, because their gravity pulls light around them. But we know that these blackholes exist because of the behaviour of the objects near them. An object can orbit a black hole just as it can orbit a star.

This is how objects around blackhole behave -

The spacetime around blackholes -

The spacetime just outside the blackhole becomes very insane.

The geodesics become insane and orbiting a

blackhole is pretty hard.

For most blackholes, things become much complicated, because most blackholes rotate.

Because of the effect called the gravitational time dilation, the time slows down on approaching a blackhole.

Time dilation around blackholes -

Black holes are massive objects.Around massive object time slow down due to curvature of a space time this effect is called gravitational time dilation

"Spaghettification" by blackholes -

When you near a blackhole, an interesting but dangerous thing happens - spaghettification.

The name clearly says what it is. The spaghettification is the vertical stretching and horizontal compressing

of an object due to tidal effects of blackholes.

Now "tidal" doesn't mean the tides of geography.

Change in the force of gravity over distance is called tidal force.

The gravity near the side facing the blackhole would be billions of times stronger than near your head. This change in gravity, makes you longer like spaghetti, called spaghettification

I hope you like it:-)

Do share..!!😊