There are many things in the universe that we have not yet known much about. Black Hole is also one of them. If you do not know What are Black Holes in Space, then let me tell you that there are some places in space where the attraction of gravity is so much that they consume every object that comes close to them, even the light is also not able to return from there, for which it is not visible to us. Such places we call Black Holes

Although we know how black holes are formed, what happens outside them, and how to detect them but even today, we have not been able to know what happens inside the black hole.

Practically it is impossible to know what happens inside the black hole. Because if we send any probe inside the black hole, then it will never be able to get out of the effect of the gravity of the black hole nor will it be able to send any signal to us.

So for now, it would be good for us to understand the theoretical concept of black holes. In this article, we will know -

1. What are black holes?
2. How many types are black holes?
3. What are the parts of a black hole?
4. How do black holes form?
5. What is the reason for the light shining near black holes?

# What are black holes?

There are some places in space where the gravitational attraction is so high that they consume every object that comes to them, and even the light is not able to return from there, for which it is not visible to us. We call these places as Black holes.

These types of places are formed when the matter of a giant star is compressed into a small space. Actually, everything inside the star tries to come close due to the force of gravity. At the same time, however, the energy released by nuclear reactions heats the star's interior. As a result, they cause gas pressure inside the star and this pressure of the hot gas pushes out so that gravity and pressure balance exactly.

But when the fuel for this massive star runs out, an unstable situation develops where the gravity becomes very strong. As a result, the outer layers of the star explode in a supernova, and the center region implodes.

If the central core of the star is massive enough, such as ten times the mass of the Sun, then nothing can stop its collapse. And finally, it becomes a black hole.

## How many types are black holes?

Usually, Black holes are of different sizes, but there are three types of Black holes depending on their size or mass - Primordial Black holes, Stellar Black holes, and Supermassive Black holes.

### 1. Primordial Black holes

The smallest ones are known as Primordial Black holes. Scientists believe that this type of black hole is formed when the Big Bang happens. These types of Black holes are small as a single atom but their mass is as large as a mountain.

### 2. Stellar Black holes

The most common type of medium-sized Black holes is called Stellar Black holes. The mass of a stellar black hole can be up to 20 times greater than the mass of the sun and can fit inside a sphere of a diameter of about 10 miles. There are dozens of stellar black holes that may exist within the Milky Way galaxy

### 3. Supermassive Black holes

The largest black holes are called Supermassive Black holes. These black holes have masses greater than 1 million suns combined and would fit inside a sphere of diameter about the size of the solar system. Scientific evidence suggests that every large galaxy contains a supermassive black hole at its center.

For example - the supermassive black hole at the center of our Milky Way galaxy is called "Sagittarius A*". It has a mass equal to about 4 million suns and would fit inside a sphere of diameter about the size of the sun.

## What are the parts of a black hole?

A black hole is made up of several different parts, such as - Singularity, Event Horizon, Schwarzschild Radius, Accretion Disk, Ergosphere, Jets of Gas.

Singularity:

This is the region of the black hole where all the mass of the black hole has been shrunk to almost zero volume.  As a result, the singularity has almost infinite density and creates an enormous gravitational force.

Event Horizon:

Event Horizon is such a radius of the black hole where, if matter or even light comes closer, it cannot escape from the gravitational pull of the black hole.

This is the radius of the event horizon. It is the radius where the escape velocity is equal to the speed of light. This is discussed in more detail later.

Accretion Disk:

The accretion disk composed of stellar material that is spiraling towards the black hole.

Ergosphere:

When the black hole is rotating, then as it spins, its mass causes the space-time around the black hole to rotate as well.  This region of a black hole is called the ergosphere.

Jets of Gas:

For some black holes, high-intensity magnetic fields are emitted perpendicular to the accretion disk.  This causes charged particles to circle these magnetic field lines and create jets of gas perpendicular to the accretion disk

## How do black holes form?

You know black holes are some places in space where the effect of gravity is so much that even the light does not come back from there, for whom we do not even see it. But do you know how it is formed?

You must have heard that a black hole is formed when the matter of a giant star is compressed into a small space. It often occurs after the supernova explosion when a big star is on the verge of ending.

But what if I tell you that a black hole can be formed from everything present in the universe, even from you. Yes, it can be.

We know that every object in this universe has its own mass,  if we compress this mass inside a sphere made of Schwarzschild radius, then it can turn into a black hole.

Now the next question that arises is what is the Schwarzschild radius?  so let's know what it is.

You know that the distance from the center of the circle to the perimeter is known as the radius. The Schwarzschild radius is also the same radius as the ordinary radius but the difference is that if we compress the mass of an object in the Schwarzschild radius, then the object will become a black hole.

Each object has different types of Schwarzschild radius, which can be extracted using this formula -

Where R = Schwarzschild radius, G = gravitational constant, M = mass of the objects, and c = speed of light.

In the chart below you can see the different types of Schwarzschild radius for different types of objects.

As you can see from this chart, the Schwarzschild radius of our sun is about 3 km. This means that if we pressurize the sun and confine it inside a sphere whose radius is only 3 km, then it will become a black hole.

Similarly, to make the earth a black hole, we have to confine it to a radius of about  9 millimeters of feet. But right now there is no way we can do it. But the stars that are many times bigger than our sun, their Schwarzschild radius are also much more than the sun.

When these types of stars finished their nuclear fuel, they are unable to keep themselves warm as before and they confine in a very small space that we call as Singularity.

The density of this singularity becomes infinite and due to this high density, its gravitational pull becomes so high that no object can come out of it and even light cannot come out of it.

Usually, this singularity is shown as a small point. But in reality, it is not physical but it is an infinitesimally small mathematical point.

## What is the reason for the light shining near black holes?

As I already mentioned, a very large black hole is present in the center of every big galaxy. Whatever comes close to this black hole consumes it, but it is not that any object is pulled directly into its center.

Actually, any objects that move near a black hole first orbits a black hole in the shape of a disk called accretion disk and only then enters the black hole.

When many objects are orbiting in this accretion disk at a high speed then due to frictional force a lot of heat is generated between them.

Such as, hot objects emit light and radiation, similarly, the objects present in the accretion disk also radiates light and radiation due to become very hot. This is the bright light that is visible to us.