A black hole is not a new phenomenon. It has always been there at the core of this incredible universe.
What is it? Firstly you have to know the structure of a star. You may know that inside a star, a process of energy happens. It is called nuclear fusion. Hydrogen turns into helium and emits a lot of energy. This energy comes to you like light and heat. So now the question arises. Do we have an infinite amount of this energy?
For us, yes. Because our generation will no longer last more than 100 years. So, for us, it's yes. But actually no. The sun or a star will someday lose all of its energy. Then it will turn into a black hole. It will have no light, as there will be no process of energy.
But you need to remember one thing. A star has to be much bigger if it wants to turn into a black hole. Our star, the sun, will not be able to turn into a black hole. It may turn into a white dwarf or something like that. If a star is much bigger, then it turns into either a neutron star or a black hole. Yes, a neutron star also may turn into a black hole, but we will not talk about neutron star today, rather today's topic will be black hole only.
When the star finishes all of its energy, its gravity shrinks it from inside. We have known that in nuclear fusion, hydrogen turns into helium. But it is also true helium can also turn into other elements. We will talk briefly about this when we discuss neutron stars. I am telling it because, for these elements, a black hole gets a great mass inside, and it becomes shrank and takes a little appearance than before. Comparing its previous version as a star, it will be very tiny.
As it is very small, its volume will be nearly zero. And the mass will be very large in amount. according to mathematics, the density will become infinite. ( density = mass/volume) This will be called a black hole then.
The black hole's gravity is so strong that it passes the other three fundamental forces of nature. As a result, the electromagnetic force ( one fundamental force) cannot escape from its gravity, like a lion and a mouse type story. You can assume, right? If a lion holds a mouse strongly, can it escape? No. as a result, electromagnetic force cannot escape. Light is electromagnetic. So accordingly, light cannot escape from a black hole. For this reason, we can't see the black hole; we can just see its shadow.
But you have seen a black hole recently? Yes, but that's not the black hole; you just saw the light around it. And from that, you assumed a black hole behind that. The light around the black hole is called an accretion disc. As you know, a black hole consumes everything, so a lot of garbages in the universe and other objects are consumed by a black hole. Like the mouth of a black is very tiny; everything cannot be consumed at a time. So other things create motion around the black hole and move like they are in orbit. The temperature of those things gets very high, and the heat energy there turns into another energy, light. And for this reason, you see a moving light around the black hole, and this is called the accretion disc.
You may hear about the event horizon. Every black hole has its region. It is a limit from which you cannot get back if you somehow get near. Simply, it's a small region around the black hole. If you put a step in that region, we have nothing to do but say you a sayonara.
Simply this is the concept of a black hole. Moreover, our galaxy also owns one . its name is Sagittarius A. every galaxy usually moves around centering its black hole.
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