Priyamvada Natarajan


Indian Astrophysicist, Professor of Astronomy and Physics at Yale University

Author Quotes

Although science as a human endeavor is not entirely objective, it still offers the best prescription for weighing evidence and making sense of the natural world. Shifting and incomplete as it may be, science is self-correcting. It is the best method we have to navigate and make sense of this wondrous universe of ours. For centuries, science has helped us chart our relationship to the natural world. And like any good map, it also points the way forward.

Astronomers now believe that black holes, despite their odd behaviors, are an inevitable consequence of the standard physics that describes the evolution of stars. The theory of stellar evolution predicts that stars born fifteen to twenty times more massive than our sun, after exhausting their fuel supply of hydrogen, will end their lives as black holes. Black holes may have exotic properties, but they are important constituents of the universe, playing a significant role in the assembly and evolution of galaxies.

At its heart, my research as a theoretical astrophysicist, mapping dark matter and understanding the formation of black holes, is driven by the same sense of wonder and search for explanation of the universe that the ancients probably felt. I am still engaged in exploring the meanings of maps and how they anchor us, matters that first intrigued me as a girl in Delhi. My work exploits the bending of light from distant galaxies, gravitational lensing, to map the invisible dark matter that causes these deflections. I also investigate the formation and growth of the universe?s most bizarre and enigmatic objects, black holes.

Cosmology, perhaps more essentially than any other scientific discipline, has transformed not only our conception of the universe but also our place in it. This need to locate ourselves and explain natural phenomena seems primordial. Ancient creation myths shared striking similarities across cultures and helped humans deal with the uncertainty of violent natural phenomena. These supernatural explanations evoke a belief in an invisible and yet more powerful reality, and besides, they rely deeply on channeling our sense of wonder at the natural world. The complex human imagination enabled ancient civilizations to envision entities that were not immediately present but still felt real. Take for instance Enki, the Sumerian god of water whose wrath unleashed floods, or the Hindu god of rain and thunderstorms, Indra, whose bow was the rainbow stretched across the sky with a lightning bolt as his arrow. The most powerful myths are the ones that force us to take huge leaps of imagination but, at the same time, help us to remain rooted.

In 1783, when an English country parson, John Michell, first proposed the idea of a ?dark star,? he could never have imagined that we would one day detect them. Michell, a polymath born in 1724, studied at Cambridge and later taught Hebrew, Greek, mathematics, and geology there. Although no portraits of him exist, a contemporary described him as ?a little short man, of black complexion, and fat.? A man of the cloth, he moved from Cambridge to a parish in Thornhill, near Leeds. Despite his religious commitments and duties, he was very much at the leading edge of science, and his reputation for originality was such that many of the active scientists of the day, the likes of Benjamin Franklin and Henry Cavendish, visited and maintained regular correspondence with him. They had much to discuss; Michell?s scientific contributions include describing the strength of magnetic fields and developing a theory for how earthquakes propagate through faults on the earth?s surface? In a letter to Henry Cavendish dated November 27, 1783, Michell anticipated that such ?dark stars? would be observable only by the impact they had on bodies revolving around them.

In 1914, our own galaxy, the Milky Way, constituted the entire universe ? alone, stagnant, and small. Cosmological research still relied fundamentally on classical conceptions of gravity developed in the seventeenth century. Modern physics and the triumphs of general relativity have shifted humanity?s entire comprehension of space and time. Now we see the universe as a dynamic place, expanding at an accelerating rate, whose principal mysterious constituents, dark matter and dark energy, are unseen. The remainder, all the elements in the periodic table, the matter that constitutes stars and us, contributes a mere 4 percent of the total inventory of the universe.

It was not the peculiar properties of an astronomical object that first inspired the term ?black hole? but rather a place ? an infamous prison. This was the scene of a gruesome incident on June 20, 1756. Sirajud-Daulah, the nawab, or ruler, of Bengal at that time, captured Calcutta from the East India Company?s troops, commanded by John Holwell, the self-proclaimed governor of Bengal. Upon surrender, the nawab confined Holwell and many other Europeans overnight in the company?s own prison cell, a tiny, dark room, roughly six meters (twenty feet) long and four meters (thirteen feet) wide, with two tiny windows, popularly known as ?the Black Hole.? Records of the incident from East India Company officials claim that 146 people were locked up in this minuscule cell, without adequate water and in extreme heat, and that only twenty-three survived. Although scholars such as J. H. Little have called these numbers into question, the Black Hole of Calcutta remains a powerful, macabre reminder of and sordid metaphor for the utter callousness of the nawab. Soon ?Black Hole of Calcutta? entered the collective consciousness as a synonym for the most horrific of experiences. When a raging fire destroyed the Op‚ra comique building in Paris on May 25, 1887, a New York Times correspondent, noting that the seats, boxes, and balcony were gone, described the building as ?an immense black hole.?

The beauty of science is that while a theory is always provisional, it represents the best evidence and explanation that we have at any moment. Though prone to revision, science is based on replicable evidence, which privileges scientific over all other possible explanations.

The journey to acceptance of an idea reveals many other facets of science ? the emotional, psychological, personal, and social dimensions that extend beyond the purely intellectual pursuit of knowledge.

Today we know that black holes exist in the centers of most, if not all, galaxies. Our own galaxy, the Milky Way, harbors one such black hole four million times the mass of our sun? Fortunately, our solar system is way too far from the center of the Milky Way for us to feel the presence of or be affected by its central black hole.

We are living in a disorienting universe, whose expansion is accelerating. And at no other period in human history have we had to contend head on so frequently with the provisionality of our understanding. We have a cosmic map that is eternally in flux. The fact that by their nature scientific truths are subject to refinement and revision is now an inescapable part of our reality. Our world view has shifted sharply in the past hundred years, rewriting the very sense of who we are, where we came from, and where we are headed.

What is perhaps most surprising is just how well some of these descriptions fit an astrophysical object that had not yet been observed. In astronomy, a black hole is a physical location of no return.

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Indian Astrophysicist, Professor of Astronomy and Physics at Yale University