An awful lot of time elapsed between the day Roger Penrose was walking to work in 1964 and the moment his phone rang while he was in the shower on the morning of Oct. 6, 2020. Back then, his walk was interrupted by “some strange feeling of elation,” as he told the Associated Press yesterday, about the moment he had his first glimmers of insight into the equations that would eventually make him famous. It was surely with another kind of elation that he answered his phone yesterday to learn that those same equations—which were the first to prove the existence of black holes—had earned the 89-year-old University of Oxford mathematical physicist the 2020 Nobel Prize in Physics.
Penrose was not alone alone in his delight. Also honored this year were astronomers Andrea Ghez, 55, of the University of California, Los Angeles; and Reinhard Genzel, 68, of the Max Planck Institute in Germany, for their research on what, to humanity anyway, is the most important black hole of all: the supermassive Sagittarius A*, which sits at the center of the Milky Way.
“The discoveries of this year’s Laureates have broken new ground in the study of compact and supermassive objects,” said David Haviland, chair of the Nobel Committee for Physics, in a statement that accompanied the announcement. “But these exotic objects still pose many questions that beg for answers and motivate future research.”
It was very much past research that earned Penrose his recognition—but research that was a prerequisite for much of the black hole science that followed. As with so many other insights into exotic physics, the road to Penrose’s work runs straight through Albert Einstein. In 1915, Einstein developed his theory of general relativity; the following year he postulated that the physics he had discovered could, at least in theory, support the idea of an exceedingly dense body—say, a collapsed star—with a gravitational pull so powerful not even light could escape. Within the maw of such an object—which was not yet known as a black hole—conventional physics and the very laws of nature as we know them would break down.
It was a nifty idea, but Einstein himself, who died in 1955, was not convinced that black holes existed. They made sense in the rarefied world of chalkboard equations, but in the far messier realm of the universe itself, the conditions might not exist to allow so tidy a stellar collapse. Nine years after Einstein’s death, Penrose took his walk to work and began contemplating “what it would be like to be in this situation where all this material is collapsing around you,” as he told the AP. “That’s a place where densities and curvatures go to infinity. You expect the physics to go crazy.”
Crazy maybe, but within a year, Penrose had set the physics straight, publishing a whole new collection of equations that put muscle on the theoretical bones Einstein had left, proving mathematically that black holes could exist in reality, not just as theories in the very big brains of very smart physicists.
“Penrose convinced physicists that black holes were tightly woven within Einstein’s mathematical tapestry,” Brian Greene, best-selling author and theoretical physicist at Columbia University, tells TIME. “Before his discovery, many imagined that black holes could only form in highly idealized conditions that might never occur in the real universe. Penrose took a mathematical sledgehammer to this possibility, establishing that in fairly commonplace circumstances, black holes—according to the math—should form. It has been nearly half-a-century since these breakthroughs and so this recognition is both well deserved and long overdue.”
Ghez’s and Genzel’s work is decidedly more recent, but even they started a while back, independently investigating Sagittarius A* as long ago as the mid-1990s. Back then the nature—even the existence—of a supermassive black hole at the center of the Milky Way was in doubt. Instead, as the Nobel Committee put it in its commendation, the best astronomers could say was that there was “an extremely heavy, invisible object that pulls on [a] jumble of stars, causing them to rush around at dizzying speeds.” Not exactly conclusive stuff.
The two researchers quickly established themselves as competitors—Ghez conducting her research with the Keck Telescope in Hawaii, Genzel using the European Southern Observatory in Chile’s Atacama Desert. Slowly, both began to peel back the mysteries of Sagittarius A*. Infrared imaging allowed them to penetrate some of the haze of dust and gas that obscures the black hole. Closer to home, they had to contend with the distorting effects of Earth’s atmosphere. They overcame that issue first with something known as speckle imaging—essentially short-exposure snapshots that freeze images in place. Later they used adaptive optics that rely on distortion-correcting mirrors.
Ultimately, their competition led to shared rewards, as the pair successfully observed the paths of thousands of stars circling the galactic center, precisely plotting the orbits of 30 of them. Their findings allowed them to take the measure of Sagittarius A*, calculating that it weighs about 4 million times the mass of the sun.
“Genzel and Ghez were the first to provide convincing observational evidence that black holes are really out there, and that a monstrous-sized one is at the center of our own Milky Way galaxy,” says Greene. “It was a heroic feat to peer at the center of our galaxy with such astonishing precision, establishing that Einstein’s math brightly illuminates reality.”
Ghez is distinguished for another reason too: she’s only the fourth woman since 1901 to be honored with the physics Nobel. More and more women are thriving in the head-cracking fields of astronomy and theoretical physics, but their work has been all too slow in being recognized. “Andrea Ghez is sure to inspire many girls to follow their passion for understanding the cosmos,” says Greene, “some of whom no doubt will one day follow her footsteps to Stockholm.” That, surely, will be a powerful human dividend of this year’s physics prizes. The scientific dividends already speak for themselves.
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