Whenever we read about celestial objects, the topic which excites us the most are Black Holes. A black hole is formed when a star exhausts its nuclear fuel and gravity overwhelms the core – the star starts to collapse under its own mass. The gravitational force crushes the atoms in the core and the star collapses into a dimensionless point, known as the singularity. Black holes have an extremely powerful gravitational pull, so strong that not even light can escape it. The event horizon – the black boundary of the black hole- is the point of no return. This magnificent and monstrous entity has the capacity to devour multiple worlds.
For a long time physicists believed that Black Holes were eternal. But, Stephen Hawking had something else in his mind. He proposed a theory, known as Hawking Radiation, which showed us that black holes too have an end.
On the quantum scale, a process known as quantum fluctuation results in the formation of a pair of particles, one an antimatter and the other a matter particle, which interact and instantly annihilate each other. The universe is in the constant process of making these virtual particles. In empty space, it is just a normal process, but around a black hole, it plays a completely different role. when these virtual particles pop into existence at exactly the event horizon or near the event horizon, the gravity of black hole comes into play. It sucks in one of the particles and the other escapes into space, the particle which escapes becomes a “real particle”, therefore, to an observer outside the black hole it would seem as if the blackhole is radiating mass and energy. As the Black hole is now losing energy, it starts to “evaporate”.
Small black holes emit radiation more rapidly than a massive one so they will evaporate faster. This is still a very slow process and calculations show that the largest black holes will take more than googol years- a “1” followed by 100 zeroes- to evaporate.
The time taken for a Black Hole to evaporate through hawking radiation is obtained by the following equation.
M is mass of Black Hole,
V is volume of black hole,
G is the universal gravitational constant,
c is the speed of light
ℏ is the reduced planck’s constant, and
M ☉ is solar mass
A black hole of mass one solar mass (1 M ☉= 2 x 10^30 kg), will take 2.1 x 10^67 years!
Supporting Theories and More Mysteries:
There are many theories that support the Hawking radiation (Bogoliubov transformation, null geodesic), but on the other hand, there are many hypotheses that oppose it as well. We can’t find an answer to these mysteries unless we have mastered our knowledge in the quantum theory of gravity.
In addition to their death, black holes are full of other mysteries as well. For example, we don’t have any evidence that can tell us what lies inside a black hole, we are still puzzled with the possibility of white holes existing simultaneously with Black Holes and many more. I guess we will have answers to these question either when we have a quantum theory of gravity or when someone volunteers to dive into a black hole.