A black hole is one of the few mysteries of the universe whose grounds only few brilliant minds have trodden upon. In layman’s terms, a black hole is a body in space that sucks everything in its radius, and does not let it get out. But this is an incomplete definition of a black hole. Let us find out some interesting facts about black holes.
Why are black holes black?
Black holes are black because light cannot escape from its reach. A common misconception of a black hole is that it attracts things and devours them. No, black holes don’t just go around destroying worlds. Black holes just devour things within their boundary. This boundary is named as the event horizon of the black hole. It is the boundary of the gravitational pull of the black holes within which the escape velocity of particles becomes greater than the speed of light.
In simple terms, if a particle has to escape the gravitational pull of the black hole, its velocity should be greater than the speed of light. But according to Einstein’s Theory of Relativity, absolutely nothing can travel faster than light. Since light itself cannot escape from the event horizon of a black hole, we cannot see it and so it appears black.
How is a black hole formed?
To understand how black holes are formed, we first need to be aware of the life cycle of a star. A star is formed when a huge cloud of hydrogen gas starts contracting due to gravitational attraction within itself. The hydrogen atoms in the cloud keep colliding with each other. As the cloud becomes smaller, the frequency of collisions increases. Eventually, hydrogen atoms just fuse and become helium atoms.
These reactions between the hydrogen atoms create a radiation or energy outflow. The gravitational pressure on the star from all sides is balanced by the energy radiations. As long as this balance is maintained, a star is stable. But for stars with a huge amount of mass, these reactions continue for a long time. This ultimately leads to the creation of heavier elements like silicon and iron. When iron is created, there is no release of energy.
Thus, in a very slow process, iron gets accumulated in the centre. This process drastically reduces the amount of energy radiation, which was hitherto nullifying the pressure of gravity. As a result, the force of gravity becomes too much for the star and the star explodes. This process is known as supernova. The end result of this blast is a small dense core with a gravitational force of very high magnitude. We call this dense core as black hole.
At this stage, we ask ourselves, “If black holes are formed on the death of a star, then is every dead star a black hole?”
Do all dead stars form black holes?
No, all dead stars do not form black holes. Relatively smaller stars like our Sun, will just turn into red-giant stars, and eventually into a cooling white dwarf star.
Only those stars satisfying a specific tipping point of mass and radius become black holes. Tolman-Oppenheimer-Volkoff limit specifies the minimum limit for mass of a star to turn into a black hole. Schwarzschild radius specifies the minimum radius of the star to become a black hole. This is the radius after which escape velocity of particles from gravitational pull becomes greater than the speed of light.
So you learned some interesting facts about black holes, Do you wish to read more of such facts? Visit our Fascinating Facts section.
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