What is a black hole? will the sun become a black hole?

What is a black hole? will the sun become a black hole?

How is a star born? There is an enormous amount of gas clouds present in the space, which majorly consists of hydrogen atoms and it is very common in all galaxies. These clouds are called nebulae. All of these hydrogen atoms present in the clouds are attracted by a gravitational force and forms as a star.This is called nuclear fusion. Core of the star consists of the enormous amount of hydrogen; it generates the Helium atoms by nuclear fusion. During the nuclear fusion, a humongous amount of energy is being generated which is what we observe as a light or heat. The gravitational force of a star is directly proportional to its mass. 

Due to this gravitational force, the outer layer of the star will be compressed towards the core, but the energy generated by the nuclear fusion will act against it and prevents the compression which makes a stable ‘star’. This is what happens in ‘Sun’, which is also a stable ‘star’. All the stars will not become a “Black Hole”. A mass of a star determines whether it will become a Black Hole or not. If the mass of a star is until eight times of our sun will become white dwarf, this is called Chandrasekhar unit. This was discovered by a scientist called Subrahmanyan Chandrasekhar from Tamilnadu at his age of 20 (1930 A.D). He had received Nobel prize for the same. If core mass of a star is greater than 1.4 times of a Solar mass, post white dwarf it will further collapses and forms a neutron star. The radius of a neutron star will be just 10 km, but its density will be very high. 

To become a black hole, core mass of a star should be > 2.8 times of a Solar mass, because nuclear fusion happens at the core of a star. At its starting stage, it fuses hydrogen atoms and produces helium atoms. Next, fuses helium atoms to produce carbon atoms followed by neon, oxygen, silicon and iron at the end. When a core of star is full of iron atoms, when it fuses, it won’t produce any energy but it will attract all the energy towards the core instead and loses its equilibrium. The huge pressure collapses the core followed by massive explosion which is called "Supernova". Post this massive explosion, it may become a black hole if it has enough mass. Black hole is not actually black in color but it is invisible in nature. The gravitational force of a black hole will be extremely high. The objects attracted by this huge gravitational force will be inside the black hole but we can’t see because... Normally, How we are seeing an object? Sunlight falls on the object, reflects back and reaches our cornea, through which we are seeing an object. But in Black Hole, due to its huge gravitational force even light can’t escape from it. Why Black Hole has such a huge gravitational force? It’s because of its huge mass. Every object’s gravitational force is directly proportional to its mass. If you want to escape from a gravitational force, you need to travel at a particular speed, which is called as “escape velocity”. For example, if you want to escape from Earth’s gravitational force, you need to travel at 11.2 Km/s, which is 615 Km/s for sun. The biggest mass in this universe is called Black Hole, because of its huge mass the gravity will be unimaginably high. 

We know very well that speed of the light is the fastest in the universe which is 300 thousand Km/s, but even light can’t escape from Black Hole. To escape from the black hole, we need to travel faster than the light. A boundary marking the limits of a Black Hole is called "Event Horizon". If any object passes this boundary line will be pulled by its huge gravitational force. For example, consider two astronauts travels into the space; one out of the two travels into Black Hole both of them have a clock with them. Both of their clock will run at a same speed until the astronaut reaches to Black Hole. Once the astronaut is near to the Black Hole, his clock will appear slower to distant observer. For him, the clock of a distant observer will look like running faster. This is due to space-time continuum. Black Hole bends the space a lot and also bends the time, with which we can even do time travel. Suppose if astronaut returns from the Black Hole, he will be in the future. In Earth, many years must have passed but he will be at the same age. This is what clearly described by Christopher Nolan in the movie “Interstellar”. But it is just fiction, in real life no one can come out from Black Hole. In case, if we want to come out a Black Hole, we need a space ship which can travel faster than light. if such a space ship is invented in future, we can explore what is in the Black Hole and also, we can do time travel.