**Annapurna Subramaniam****October 12, 2020 4:51:34 PM IST**

This year’s Nobel Prize in Physics is awarded to research related to black holes. Half of the prize went to British Professor Sir Roger Penrose for his theoretical research, which confirmed that the black hole was a strong prediction for Einstein̵

Prof. Penrose was awarded the prize for research done about 55 years ago. His research used Einstein’s general theory of relativity to prove that the singularity and black hole formulation are mathematically possible. The Penrose-Hawking singularity theorems, as this set of results is called, also answer the question of when gravity gives rise to singularities. These theorems have used the Reichuduri equation, a key ingredient to explain space-time features and gravitational focusing properties in cosmology.

*Read also: The Nobel physics of black holes by Penrose, Hawking deals with the work of Indian physicist Amal Reychaudhuri*

Although the above study was a joint effort between Sir Roger and Stephen Hawking, the latter came to the fore. Penrose, on the other hand, did not attract media attention and limited himself to academic pursuits. Penrose is a versatile intellectual and a talented mathematician with broad interests. One cannot help but wonder why it took so long for the Nobel Committee to award him the prize.

**Significance of Penrose’s discovery**

From observing the stars in our galaxy and others, we know that stars form and die. Low-mass stars, like our Sun, live long and die like “white dwarfs.” Larger stars that are eight times the mass of our Sun die in a spectacular explosion we call a supernova. For stars that are much more massive – say, more than 20 times the mass of the Sun – the central crumbling core is thought to be much, much larger. The core becomes extremely dense and compact, forming a black hole.

This unusual event, when a black hole forms and matter breaks up to limits beyond the nuclear scale, is difficult to describe theoretically. A combination of gravity and quantum physics and mathematics is required. The closest we can get without this theoretical work is a vague estimate of the density of the black hole from the study of other compact objects in the universe.

Only recently was the first direct image of a black hole from a nearby galaxy (M87) captured by astronomers around the world, in a remarkable feat. However, there is still a huge gap in the modern understanding of black holes. We are yet to understand the peculiarity that was present in the beginning, before the great explosion that supposedly gave rise to everything in the universe. We also do not know what happens to an observer who falls into a black hole singularity.

Before the Penrose-Hawking singularity theorems appeared in the 1970s, it was thought that singularities formed only in certain situations. For example, in the case of a supernova explosion, in which a black hole forms from the collapse of the star’s core, it may be possible for a rotating star to partially counteract its own gravity. It was thought that a singularity would not form in these circumstances – until Penrose-Hawking’s singularity theorems refuted this belief. He showed that a singularity is formed in every case when there is a horizon of events – the conditional boundary around a black hole, beyond which no light can escape.

**Much needed recognition for theoretical work**

If there were two ideas that stimulated the imagination of a very theoretical astrophysicist, it was black holes and Einstein’s general theory of relativity. One of the most fascinating questions in astrophysics remains “what is a black hole?” It is a curiosity that keeps both students and astrophysicists interested. Of the more real consequences, many nations have invested heavily in building experimental detectors to detect the presence of a black hole. One of these experimental results, led by Gas and Genzel, won half the Nobel Prize in Physics in 2020. And yet, one wonders, is the funding of international megaprojects like LIGO and VIRGO not a recognition of real theoretical work that needs recognition?

Black hole detection experiments have been proposed, funded and are now fully functional research centers. The 2017 Nobel Prize in Physics was awarded to ** Rainer Weiss,, Barry S. Barish** and

**for a decisive contribution to the LIGO detector and the observation of gravitational waves. The signal, which was detected using the LIGO observatory, comes from the merging of two black holes. Again, it was surprising to find that the prize was not awarded to those who made the actual predictions. Meanwhile, the world lost one of the most brilliant minds in astrophysics, Professor Stephen Hawking, in 2018. The Nobel Prizes are not awarded posthumously. So Hawking, for all his contributions, will never receive a Nobel Prize.**

__Kip S. Thorne__**Penrose’s overdue decades for the Nobel Prize?**

During a brief visit to the Indian Institute of Astrophysics on January 2-9, 1994, Sir Penrose gave lectures at an international conference on particle physics (not an accelerator). We expected him to receive the Nobel Prize in the next few years. At that time I was a doctoral student at the Institute and we were excited to hear him speak and communicate with him. During the conference, Prof. Penrose also wrote an article “*On* t**the role of gravity in the quantum reduction of the state***‘* for * Proceedings of the International Conference on Particle Physics without Acceleration,,* edited by the then Director of the IIA, Prof. R Cowsik. That same year, Prof. Penrose became a knight for his “merits in science.” It will take him another 26 years to win the Nobel Prize for his contribution to the theoretical understanding of black holes. It is gratifying to see, despite the delay, that Sir Penrose has been recognized by the Nobel Committee.

Subramanyan Chandrasekhar, an astrophysicist of Indian descent, received the Nobel Prize in Physics in 1983 for his work in the early 1930s. It took about 50 years for the Nobel Committee to recognize his work. Let’s not forget that Albert Einstein never won a Nobel Prize for his eternal work on the General Theory of Relativity. Many great theoretical works and discoveries have been awarded belatedly or missed altogether from the consideration of the Nobel Prize.

Maybe it’s because Alfred Nobel envisioned the award to be given to those inventions that are most beneficial to humanity?

*The author is the director of the Indian Institute of Astrophysics, Bangalore, and works on the study of star clusters, the evolution of stars and populations in galaxies and Magellanic clouds. She tweeted at @fiddlingstars*