Black Hole and Hawking’s Radiation

-By Monika Sachan

A hole, something hollow with no matter inside but Black Hole, can be anything, not hollow.

The black hole is an area or region in space-time where the matter is packed closely that results in a very strong gravitational pull. The black hole is black due to the fact that not even light can escape from it.

With advancements in instruments(telescopes), space agencies have been able to muster images of mysterious celestial objects in space, like black holes.

Theory of relativity prognosticates, as the mass is compact, deformation in space-time causes black hole to form.

For many centuries, the idea of black hole has been present. Theory of general relativity by Einstein divine black holes and showed that a small, dense stub core is left, when a massive star dies.

When the force of gravity is so strong and overshadows all other forces, a black hole is produced. This fact is mathematically proven by equations, which happens when the mass of the core is more than three times the mass of the Sun.

Detection is directly not possible, even sometimes, the telescope that detects x-rays, light, or other forms of EM radiation fails to do so accurately. The presence of these black holes can be detected with their effects on other celestial bodies(matter) nearby.

Genesis of Black Hole:

When a massive star dies, its stub forms black hole in a supernova explosion. Stars with massive mass, at least three times that of the Sun, collapses under the influence of gravity.

In most cases, black holes are identified when a start passes closer enough or vice-versa. In both the cases, pulling effect of the star, within itself, results in tearing apart of that star result of which is the acceleration and heating up of attracted matter.

Singularity is a point or center in a black hole, where the matter is indefinitely dense. Mathematically, the singularity is a point at which a function takes an infinite value (definition from Oxford Languages).

When a massive star collapses inward upon itself due to massive gravitational pull, results in the falling of constituent matter, from all sides, compresses the dying star to almost zero volume point with infinite density called the Singularity.

Structure of black hole and Hawking’s Radiation:

Albert Einstein’s general theory of relativity provides details for the calculation of black hole structure.

The center of black hole constituted by singularity is secluded by the object’s surface known as Event Horizon.

Light cannot escape from black hole as the escape velocity inside the black hole is greater than the speed of light.

German astronomer, in 1916, revealed the existence of bodies(stellar) that emits no radiation. Hence the name for the radius for the event horizon known as Karl Schwarzschild radius. The size of the radius is proportional to the mass of collapsing star.

Supermassive black holes are formed by the large volume of interstellar gas that collects and collapses into supermassive black holes at the center of quasars and galaxies. These kinds of black hole have non-stellar existence.

Other non-stellar black holes were proposed by Stephen Hawking, a British Astrophysicist. According to his theory, there may be possibly numerous tiny black holes having a mass of more or less comparable to asteroids. Also, he believed that these black holes were created during the creation of the Universe and Big-bang. These are mini black holes.

How a Black hole tear apart a star
Source: NASA Goddard youtube cahnnel
Black hole eating a star Source: Bright side youtube channel

The quantum effects in the vicinity of event horizon radiate black body radiation, Hawking’s Radiation, named after the physicist Stephen Hawking. He postulated this theory in existence in 1974.

In order to lose energy, black holes evaporate and radiate energy into the wider universe. Redshifting effects and analysis of black hole thermal equilibrium is useful for understanding evaporated and radiated spectrum of black holes. The Quantum Entanglement effect is also helpful in consideration as well.

One pair of photons appear just outside the event horizon and the other pair close to the event horizon due to the Entanglement effect.

Due to the conservation of law, it is believed that one of these photons passes beyond the event horizon while the other one escapes in-universe. Extreme gravity tears escaped photon apart. Due to this radiation (Hawking’s Radiation), the mass and rotational energy of black hole reduce, known as black hole evaporation. Radiation ultimately results in the shrinking and vanishing of black hole that does not gain any mass from any other means.

Hawking’s theory is dependent on particle-antiparticle radiation or in other words, positive and negative energy. This theory is very useful in bridging the gap between Quantum Mechanics and the Theory of Relativity, two completely different Sciences.

Hawking’s theory gives vision to scientists, physicists, and to common people but at the same time, many questions are still unanswered. Also, his theory is based on pre-notions that he considered useful to give complete meaning or, one can say support, his theory.

The Unsolved mystery of information paradox by Stephen hawkings? Know everything along with the backdrops  

According to general relativity, A black hole is formed when the matter is too large and gravity destroyer the material till the central point and this phenomenon forms a super strong gravitation force which means even light cannot escape the inside of a  black hole. So, one cannot see the inside of the black hole from the outside.

Nothing can go from inside can go to the exterior of a black hole. However, it is possible to fall through the exterior.

Hawking’s theory & physical paradox

In 1991 Hawking made a bet with Kip Torne stating that any information that falls into a black hole will be destroyed and cannot be retrieved and this is called the black hole information paradox.

Later somewhere around 1973-75, hawking and Jacob Bekenstein stated that space-time bends slightly toward a central point called a singularity. Due to radiation (Hawking’s Radiation), the mass and rotational energy of the black hole reduce, known as black hole evaporation. Radiation ultimately results in the shrinking and vanishing of a black hole that does not gain any mass from any other means and that’s where things don’t felt right!!

 The flaws of the information paradox

The concept of evaporating led to the contradiction of ideas resulting in a physical paradox. According to the no-hair theorem, the hawking radiation can be independent of material entering the black hole. Hence, The transformation of the state (from pure quantum state to Hawking radiation) may destroy the information about the original state and this theory doesn’t align with the vital principle of quantum mechanics.

Is that it?!! Not really

Everyone thought the mystery is solved when Leonard Susskind came up with the proposal “black hole complementarity”

According to this, the information is reflected and passes through the horizon however it cannot escape the horizon, and it is not possible to observe and witness both inside and outside the black hole’s horizon simultaneously. This notion successfully satisfied hawkings but miserably failed in convincing Thorne.

A series of attempts were made by different physicists to encounter this paradox however, it became an unsolved riddle.

In 2012, Joseph Polchinski turned the table with a different approach to the paradox. Joseph concentrated on how much information can come out of a black hole. He stated that “instead, in-falling observers would encounter a literal wall of fire at the event horizon, burning up before ever getting near the singularity.





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