We know how star is born, now let’s understand what happens when it dies. Does all star become a black hole when they die? will our sun become a black hole one day?
Black holes are the results of super massive collapsing stars. A star with a mass 20 times more than our sun may form a black hole at the end of its life. When a star runs out of fuel and the nuclear reaction comes to an end the gravity becomes the dominant force and push the star and all the matter present inside it towards the core. If the star is massive enough then it might collapse into a black hole and distort the space time up to such extent that even light can’t escape the gravity.
When the mass of the star gets concentrated at the core, the density is so high that it is considered to be infinite and the gravity becomes so powerful that even light cannot escape that region of space and time. It is the region of space and time where all the physics laws break and everything acts in a weird way. Its gravity is so large that even light cannot escape once it crosses the even horizon. That’s why beyond the event horizon everything seems to be black as nothing is being reflected from that region and only, we can see is a pure black body.
Black hole has three layers – Ergosphere , event Horizon and Singularity
Ergosphere – Also called outer event horizon, is a region located outside rotating black holes. You can enter this part of black hole and come out without any physical damage but the space-time still gets distorted here.
Event Horizon – This is called point of no return. Once something has entered this region of black hole then there is no way of coming out and it will move only in one direction that is singularity. You will never see anything crossing the event horizon if you are at a safe distance from a black hole. For example, if I enter a black hole then you would see me slowly turning into red and then vanishing. No information can come out of event horizon not even light of the falling body.
Singularity – This is the place where all the mass of the black hole is concentrated. The density of this region of black hole is infinite and so the gravitational field. We still have very less idea on how the fundamental laws of physics will work at this point as the laws of normal spacetime breaks down in singularity.
If you imagine yourself standing near the event horizon of a black hole then you can see your back head right infront of you as the light from your back head will revolve around black hole and will hit your eye. This is due to the immense gravitational force of the black hole which traps even the light and make it revolve around itself just like planets around the star. The gravity of black hole is beyond imagination.
The question is how to know its presence if we can’t see them? We can’t see a black hole but for sure we can see its gravitational effect on its neighbours. If we see a star revolving around nothing then it is concluded that the star is revolving a black hole. We can only detect black hole when it interacts with any celestial body which is near to it.
Our sun will never become a black hole as it does not have enough mass to tear the fabric of spacetime and create a singularity. It will just stop its nuclear reaction and become a white dwarf with much less energy being emitted from it.