Stephen Hawking’s final theory of black holes -The Hawking radiation

When a massive star dies, it leaves a small but dense remnant core in its wake. If the mass of the core is more than 3 times the mass of the sun, the force of gravity overwhelms all other forces and a black hole is formed. Imagine the size of a star is 10 times more massive than our sun being squeezed into a sphere with a diameter equal to the size of New York City. The result is a celestial object whose gravitational field is so strong that nothing, not even light can escape it. The history of black holes was started with the father of all physics, Isaac Newton. In 1687, Newton gave the first description of gravity in his publication, Principia mathematica, that would change the world.

Then 100 years later, John Michelle proposed the idea that there could exist a structure that would be massive enough and not even light would be able to escape its gravitational pull. In 1796, the famous French scientist Pierre-Simon Laplace made an important prediction about the nature of black holes. He suggested that because even the speed of light was slower than the escape velocity of black hole, the massive objects would be invisible. In 1915, Albert Einstein changed physics forever by publishing his theory of general relativity. In this theory, he explained space time curvature and gave a mathematical description of a black hole. And in 1964, john wheeler gave these objects the name, the black hole.

The Gargantua in Interstellar is an incredibly close representation of an actual black hole

In classical physics, the mass of a black hole cannot decrease; it can either stay the same or get larger, because nothing can escape a black hole. If mass and energy are added to a black hole, then its radius and surface area also should get bigger. For a black hole, the radius is called the Schwarzschild radius. The second law of thermodynamics states that, an entropy of a closed system is always increases or remains the same. In 1974, Stephen hawking– an English theoretical physicists and cosmologist, proposed a groundbreaking theory regarding a special kind of radiation, which later became known as hawking radiation. So hawking postulated an analogous theorem for black holes called the second law of black hole mechanics that in any natural process, the surface area of the event horizon of a black hole always increase, or remains constant. It never decreases. In thermodynamics, black bodies doesn’t transmit or reflect any radiation, it only absorbs radiation.

When Stephen hawking saw these ideas, he found the idea of shining black holes to be preposterous.  But when he applied the laws of quantum mechanics to general relativity, he found the opposite to be true. He realized that stuff can come out near the event horizon. In 1974, he published a paper where outlined a mechanism for this shine. This is based on the Heisenberg uncertainty Principe. According to the principle of quantum mechanisms, for every particle throughout the universe, there exists an antiparticle. These particles always exist in pairs, and continually pop in and out of existence everywhere in the universe. Typically, these particles don’t last long because as soon as possible and its antiparticle pop into existence, they annihilate each other and cease to exist almost immediately after their creation.

In the event horizon that the point which nothing can escape its gravity. If a virtual particle pair blip into existence very close to the event horizon of a black hole, one of the particles could fall into the black hole while the other escapes. The one that falls into the black hole effectively has negative energy, which is, in Layman’s terms, akin to subtracting energy from the black hole, or taking mass away from the black hole. The other particle of the pair that escapes the black hole has positive energy, and is referred to as hawking radiation.

The first-ever image of a black hole by the Event Horizon Telescope (EHT), 2019

Due to the presence of hawking radiation, a black hole continues to loss mass and continues shrinking until the point where it loses all its mass and evaporates. It is not clearly established what an evaporating black hole would actually look like. The hawking radiation itself would contain highly energetic particles, antiparticles and gamma rays. Such radiation is invisible to the naked eye, so an evaporating black hole might not look like anything at all. It also possible that hawking radiation might power a hadronic fireball, which could degrade the radiation into gamma rays and particles of less extreme energy, which would make an evaporating black hoe visible. Scientists and cosmologists still don’t completely understand how quantum mechanics explains gravity, but hawking radiation continues to inspire research and provide clues into the nature of gravity and how it relates to other forces of nature.