Why 2020 is the year of black holes
The Nobel Prize in physics for 2020 has been shared by Roger Penrose, the mathematical physicist, for his work on the theoretical basis of black holes, and astronomers Reinhard Genzel and Andrea Ghez, who led independent teams, for verifying the existence of such a black hole at the center of our Milky Way galaxy.
Penrose showed that the consequence of Einstein's general theory of relativity is the formation of black holes, not only in collapsing stars but also in certain dense regions of space. Such black holes capture everything: nothing can come out, not even light. Genzel and Ghez and their respective teams independently showed by tracking the trajectory of a star that a superheavy object — around 4 million solar masses — exists at the center of the Milky Way galaxy. Ghez is the fourth woman to win a Nobel Prize in physics, the first one being Marie Curie, who won in 1903.
The Nobel Prize has assumed a halo that it does not deserve. Alfred Nobel was paying blood money for creating dynamite, which magnified the horror of war. But in sciences, it is still seen as the touchstone of greatness, even as its value is going down in peace and literature, which are seen to be far more guided by politics. How else do we explain Kissinger's peace prize in 1973 and Churchill's literature prize in 1953?
There are two Indian connections to black holes. The first is through physics. It was Subrahmanyan Chandrasekhar, an Indian physicist, who had shown in 1930 that if a star was larger than 1.4 times the solar mass, it would not stop collapsing. Chandrasekhar was the nephew of C.V. Raman, who was India's first Nobel laureate in physics. Chandrasekhar received the Nobel Prize for physics in 1983. He moved to the United States in 1936 and assumed American citizenship in 1953. Below the mass now known as the Chandrasekhar limit, the star would become a white dwarf. If the mass of the star was higher, he did not speculate on what would happen.
We now know that it would blow up in a supernova, and then collapse with its atoms squeezed into the nucleus-sized spaces forming a neutron star; or not stop collapsing at all, thereby creating a black hole.
The second Indian connection, and an unhappy one, is how the term black hole came about. It is now established that Robert Dicke and John Wheeler, both physics professors from Princeton University, were the first to coin the term black hole for the gravitational collapse of a star creating a singularity. And Dicke's family remembers his use of the phrase black hole whenever he could not find something in the house, asking whether it had disappeared into the Black Hole of Calcutta. Black Hole of Calcutta was, as we know, was a grossly overblown myth about a number of English soldiers and East India Company European employees being shut in a small prison room with two small windows, killing a number of them due to suffocation. The numbers that were claimed then by the East India Company have been disputed by a number of historians, but provided the justification of wholescale killings, plunder and the seizure of lands that finally became the British Empire in India. It overshadowed—in English minds—the innumerable colonial massacres that the British carried out and the devastating famines that accompanied British rule.
Einstein's general theory of relativity, formulated in 1915, led Karl Schwarzschild, an astronomer serving in the German Army in World War I, to publish a solution to Einstein's field equations, which showed that if matter and energy exceeded a certain bound, it would cause space-time to collapse on itself, producing a singularity—or a black hole. The external world would feel its gravitational effect, but no mass or even light could escape from such a black hole.
Though Einstein's general theory predicted the possibility of black holes, even Einstein did not really believe that they could exist. One major objection about the formation of black holes was that it demanded the collapse to be symmetrical, and it was argued that no collapse could be perfectly symmetrical, and therefore the formation of a black hole was a remote possibility. Penrose showed, using a mathematical topology that he developed known as the Penrose transform, that unlike other derivations for black holes, his approach did not require perfect symmetry of the collapsing matter. Applying the general theory of relativity, Penrose showed that the only requirement was enough density of matter in a given space, and this condition was enough for the formation of a black hole.
Such a theoretical derivation is not enough for physicists; physics needs experimental evidence to confirm a theory. Or at least theory alone is not enough for the Nobel Prize and the Swedish Academy that privilege experimental physics over theory. This was the argument against giving Einstein the Nobel Prize, though the reasons ran far deeper.
Einstein had become world-famous for having turned the familiar world of Newtonian physics upside down. But despite his worldwide fame, he had his enemies both in Germany and in academia because of his opposition to World War I, his radical views including socialism, and the fact that he was Jewish. The prevailing orthodoxy of physics, including the Nobel Committee, dismissed Einstein for all these reasons and argued that Einstein's theories were only theories, and lacked experimental proof.
To end this argument, the English astronomer Arthur Eddington in 1919 proposed an experimental verification of the theory of relativity. If a massive object curves space around itself due to its mass, it should be possible to observe this curvature by measuring starlight passing close to the sun during an eclipse. Eddington did this during a solar eclipse of 1919 and was able to show that the results closely agreed with the predictions of Einstein's general theory of relativity. The Times of London declared, "Revolution in Science: New Theory of the Universe," a New York Times headline wrote, "Lights All Askew in the Heavens." Einstein became a rock star in physics, a stature unmatched by any scientist.
But even that did not get him the Nobel Prize in 1920 and 1921. The science historian Robert Friedman wrote in his book The Politics of Excellence that the Nobel Committee could not stomach a "political and intellectual radical, who—it was said—did not conduct experiments, crowned as the pinnacle of physics." The 1920 prize went to an eminently forgettable discovery of an inert nickel-steel alloy, and in 1921, the Nobel Prize was not awarded. By then, denying Einstein was possible for the committee even if it meant not bestowing the prize on anyone at all. Finally, in 1922, Einstein was awarded the held-over Nobel of 1921, not for the theory of relativity for which he was most famous, but rather for the discovery of the photoelectric effect—the discovery that light also behaves as a particle—that Einstein had made in 1905. It was also the same year that he had published the first of his relativity papers, on the special theory of relativity.
Penrose's work had laid a firm mathematical basis for black holes and, in the heart of such a hole, a space-time singularity. Stephen Hawking developed this concept using the general theory of relativity to show that if we project time into the past, we would find that the entire universe started with such a singularity in time, or a Big Bang. Penrose and Hawking worked together in the 1960s, and their work has been widely hailed for unraveling the origins of the universe. Although Hawking achieved iconic status, as perhaps the most famous physicist after Einstein, he never received the Nobel Prize. Penrose's Nobel Prize for the space-time singularity is perhaps a shamefaced bow to Hawking for the Nobel Prize that he never received.
Theories in physics open up possibilities to understand our universe. But without experimental verification, there is still a nagging doubt in the minds of the Nobel Committee that some new phenomena could contradict the theory. So the search for experimental verification is viewed as the supposed gold standard of physics. And when it comes to astrophysics, it is a daunting task to prove theories with experiments on stars that would have to be observed from light-years away. This is why Chandrasekhar's Nobel Prize took more than 50 years, Penrose's 55, to be awarded. And as Nobel Prizes are not given posthumously, physicists like Hawking are never awarded for their remarkable contributions.
An observation that confirms the existence of a superheavy object that does not emit any energy would provide verification of Penrose's prediction of a black hole. This is what Genzel and Ghez achieved, finding that the Milky Way galaxy, like most galaxies, hosts a massive black hole at its center. Dr. Andrea Ghez is a professor at the University of California, Los Angeles, and Dr. Genzel the director of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. Ghez's team used the Keck Observatory in Hawaii, while "Genzel's group used telescopes in Chile operated by the European Southern Observatory (ESO)." Both the teams have been in "competition" for some time and have jointly received many honors. In this case, it was over tracking stars close to the galactic center of the Milky Way. Both teams tracked the same star, called S02 by Ghez's team and S2 by Genzel, which had a very short orbiting period around the center of the Milky Way of only about 16 years compared to the sun's orbit of 200 million years. Both teams' results, using different telescopes and data sets over decades, have shown that they are in close agreement that a superheavy object, with a mass of about 4 million suns, lies at the center of our galaxy. In the staid language of the Nobel Committee, "A robust interpretation of these observations is that the compact object at the Galactic center is compatible with being a supermassive black hole."
We have come a long way from Einstein's theory of relativity and Chandrasekhar's stellar collapse. Let me end with Chandrasekhar's Nobel speech, where he quoted the only Nobel laureate in literature from India, Rabindranath Tagore:
"Where the mind is without fear and the head is held high;
Where knowledge is free;
Where words come out from the depth of truth;
Where tireless striving stretches its arms towards perfection;
Where the clear stream of reason has not lost its way into the dreary desert sand of dead habit;
Into that heaven of freedom, let me awake."
Often quoted, perhaps overused, but nevertheless appropriate for our dark times.
Prabir Purkayastha is the founding editor of Newsclick.in, a digital media platform. He is an activist for science and the free software movement.