Indian Scientist behind 2020 Nobel prize Physics

             From Black Hole to Nobel Prize

The 2020 Nobel prize revolves around one of the most fascinating and challenging topics in Physics, shedding light on the 'Darkest Secrets' of the Universe ever known to mankind.Even, the greatest Physicist of 19 th century prof.Albert Einstein himself had a perplexed idea of it.

Yes, It is a Black hole. A Black Hole is a giant ball of mass whose field of gravity is so intense that even Electromagnetic waves like light can't  escape it, which makes it very difficult for astronomers to observe. A supermassive Black Hole is a direct consequence of Einstein's General Theory of Relativity, which was published in the year, 1915.

Einstein himself didn't believe in the existence of Black Hole Proving which receives 2020 Nobel in physics .

Artist’s conception of a Black Hole.

 This year Nobel prize in physics was   awarded to three scientist, Dr.Roger penrose, who is an English Mathematical Physicist and professor of Mathematics at University of Oxford.Dr.Reinhard Genzel, who is a German Astrophysicist and an emeritus professor at University of California, Berkeley and Dr.Andrea Ghez ,who is an American Astronomer and professor at University of California, Los Angeles (UCLA) .Together these three scientists helped revolutionize our knowledge of one of the 'Darkest Secrets' of the Universe i.e., A supermassive Black Hole.

Dr.Roger Penrose, extreme left, Dr. Andrea ghez , Dr.Reinhard Genzel extreme right.

The history of Black Hole goes way back to 18 th century, when it was first considered that objects whose gravitational fields are too strong for an Electromagnetic Wave like Light can't escape by John Michell, an English Natural Philosopher and Pierre Laplace, a German Mathematician. In the meantime, the first modern solution of Einstein's General relativity, that would characterize a Black Hole was  founded by Karl Schwarschild ,a German Physicist in the year 1916. He pointed out that the equations contained an apocalyptic prediction: In effect, cramming too much matter and energy inside too small a space would cause space-time to collapse into a point of infinite density called a singularity [In short where mass density tends to infinity]. In that place ,if you could call it a place - neither Einstein’s equations nor any other physical law made sense.

Einstein could not fault the math, but he figured that in real life, nature would find a way to avoid such a calamity.

In 1965, however, a decade after Einstein’s death, Dr. Penrose , one of the world 's most prominent Physicists slammed the door on Einstein’s hopes.

Penrose, helped placed the previously idealized concept of Black Hole on a sound theoretical footing in the 1960's by applying 'Topology' [Topology is the mathematical study of the properties that are preserved through deformations, twistings, and stretchings of objects.] to Einstein's General theory of relativity.

In the year 1964 , Penrose derived a topological picture of Gravitational Collapse [It is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward, towards the centre of gravity] with assuming spherical symmetry.

He introduced new mathematical methods including the notion of 'Trapped - Surface' for his work.

He then encapsulated all that information graphically using certain techniques thereby showing how stars collapse to form Black Holes. With well known physicist  Stepen Hawkings, Penrose showed that there would be a singularity where time has a beginning, which is known as 'The Penrose–Hawking singularity theorems' , inspired from 'Rai choudhury s Equation'.I shall come to it later.

                Penrose and Hawking proved that, for stars of a certain type, black holes are a pretty much unavoidable outcome of stellar collapse. Prior to this groundbreaking work, most physicists thought that black holes were merely mathematical curiosities which appear in general relativity but that they would not exist in reality. Instead it turned out that black holes are hard to avoid in stellar collapse and that the universe should be full of them.... The story of the discovery of black holes demonstrates vividly how powerful pure mathematics can be in the quest to understand this mysterious Nature. Dr. Penrose was awarded apparently

$1.1 Million prize, for proving that black holes must exist if Albert Einstein's theory of Gravity namely General Theory of Relativity (GTR) is right.

Now, when it comes to General relativity and cosmology, the role of Dr. Amal Kumar Raychaudhuri is tremendous . Prof.Raychaudhuri was an Indian physicist, and past faculty at Presidency college, Kolkata ,known for his research in general relativity and cosmology. His most significant contribution is the eponymous 'Raychaudhuri equation' , which demonstrates thatsingularities arise inevitably in general relativity and is a key ingredient in the proofs of the Penrose–Hawking singularity theorems.

Penrose in collaboration  with cosmologist Stephen Hawkings used an equation that A.K.Raychaudhuri had published in the Journal  'physical Review' in 1955, [https://journals.aps.org/pr/abstract/10.1103/PhysRev.98.1123]. 

                               

                                          Amal Kumar Raychaudhuri (1923-2005)

                   

              For more than 50 years, physicists had suspected that there may be a black hole at the centre of the Milky Way. But the technology had to catch up before this idea could be demonstrated.

In the 1990s, Dr. Reinhrd Genzel, from the Max Planck Institute for Extraterrestrial Physics in Garching Germany, and Dr.Andrea Ghez , professor and astronomer at UCLA, who became fourth women to receive Nobel Prize in Physics, developed methods to see through the huge clouds of interstellar gas dust to the centre of the Milky way,  stretching the limits of technology, they infused new techniques to compensate for distortions to their observations caused by the Earth's atmosphere, building new unique instruments, committing themselves to long term research. Their work has provided the most convincing evidence of a supermassive black hole at the centre of the Milky way.

The two astronomers and their competing teams have spent nearly three decades using the world’s best ground-based infrared telescopes to peer through the dusty gas of our galaxy’s center. Here, deep in the heart of the Milky Way, they saw dozens of stars looping pell-mell around an invisible center. By tracing the stars’ motions over years, the astronomers mapped out the stars’ orbits — which, it must be emphasized, is no mean feat: These stars are more than 26,000 light-years away and crowd together in the field of view like moving small snowballs.

              

   A time-lapse of observations from the European Southern Observatory’s telescope in Chile showing stars orbiting the Milky Way’s central black hole over 20 years. Credit: ESO/MPE

The orbits revealed that the stars revolve around an unseen, unmoving, and compact something-or-other with the mass of 4 million Suns. The best explanation is a supermassive black hole, which astronomers call Sagittarius A*.

                                                

      Artistic representation of the Orbit of S2 around a very     compact object (A super massive Black Hole)

This artist’s impression shows the path of star S2 took as it swung by the supermassive black hole at the center of the Milky Way. As the star approached the black hole, its light had to fight the black hole's immense gravitational field. The light lost energy in the process, causing the star's color to shift slightly to the red (exaggerated here for effect).

The star (S2) , follows an elliptical 16 years orbit, it make it closest approach, with 20 billion kilometers to Sagittarius A* , last year (2019).

If Isaac Newton's classical description of Gravitation Theory holds true, S2 should then continue along exactly the same path through space, as on its previous  orbit .But it didn't.Instead, it followed a slightly diverging path, the axis of its ellipse shifts slightly as observed by the team of Genzel and Ghez in European Southern Observatory . The phenomena of this orbital shift is called  schwarzschild Precession, would in time, cause S2  to trace a 'Rosette' shaped Orbit as predicted by Einstein's General Relativity.As well as another stringent test of relativity, the researchers say that their detailed tracking of S2 will allow them to study how much invisible material, including dark

matter and smaller black holes, exists around Sagittarius A*. And that could help them understand how such behemoths grow and evolve.

                 All of these breakthrough techniques bring us closer than we have ever come to the edge of the unknown, offering novel ways to study the most mysterious objects in the cosmos and to test our most fundamental theories.The results of the past several years research ,have allowed us to ask questions we could never have formulated before. But more importantly, they allow us to dream big. The work celebrated by 2020 Nobel Prizes in Physics is transformative.This is not just an old adventure coming to its triumphant conclusion ,it’s a new one beginning. As we probe ever closer to the horizons of the black holes, nature might have new surprises in store.