Black Hole

by Marcia Bartusiak

  Meanwhile, Chandra continued to pursue the mystery of a white dwarf star’s fate, which only increased his perplexity. He published these concerns in 1932, this time in a German journal to avoid possible rejection by British referees. In the article’s final sentence, he wrote, “We may conclude that great progress in the analysis of stellar structure is not possible before we can answer the following fundamental question: Given an enclosure containing electrons and atomic nuclei (total charge zero), what happens if we go on compressing the material indefinitely?” Indeed, what does happen to the star? By putting his final thought in italics, Chandra was likely pressing the astrophysical community, which was largely uninterested at this stage, to pay attention. The top Britishers in stellar physics—Eddington, James Jeans, and Edward Milne—were too busy arguing with one another at meetings on the exact construction and composition of a star’s innards to pay attention to the theories of a lowly graduate student. The only thing the three combatants could agree on was that a star would never collapse to a point.

  After the publication of his 1932 paper, travel and other astrophysical questions diverted Chandra for a while, but once he obtained his PhD and was elected to a fellowship in Cambridge’s Trinity College, Chandra came back to the problem. “It is necessary to emphasize one major result of the whole investigation,” he wrote in 1934, “namely, that it must be taken as well established that the life-history of a star of small mass must be essentially different from the life-history of a star of large mass. For a star of small mass the natural white-dwarf stage is an initial step towards complete extinction. A star of large mass … cannot pass into the white-dwarf stage, and one is left speculating on other possibilities.” In other words, low-mass stars would assuredly die as white dwarfs, but what fate befalls a star of higher mass, whose central core steps over the limit? What could possibly happen to it?

  The idea occurred to him that his finding might lead to new physics, “but I kept away from it …,” he said. “I was not willing to draw that conclusion.” As a foreigner at a university with so many notable figures in physics, he often felt that he didn’t belong. “It seemed to me that there were … far too many people doing important things, and what I was doing was insignificant in comparison. I suppose I was afraid,” he recalled.

  Yet Chandra quietly continued working on the problem. During a visit to Russia, Soviet scientists convinced him that no astronomer would take his limit seriously until he demonstrated that a good sample of white dwarf stars, across a range of densities and properties, never venture beyond the critical mass limit. He decided to take on the challenge, which involved solving a complex differential equation for each star using a clunky desktop calculator. In the end, Chandra completed an eighteen-page paper, teeming with calculations. Finished on 1 January 1935, it was headed for publication in the Monthly Notices of the Royal Astronomical Society. A graph he included in the paper visually portrayed his startling bottom-line: as a white dwarf star grew smaller and smaller with increased mass, its radius approached zero. Past a certain weight, a white dwarf star simply shriveled up toward nothingness. Chandra’s earlier work had been based on approximations. This time he had an exact solution.

  Achieving that goal was a draining experience for him. It involved several months of twelve-hour days. “Involved in the puzzles of the interior of stars, battered by differential equations, boxed by numerical calculations, impeded by ignorance, rushed on by the dawning of the New Year,” he wrote his brother Balakrishnan soon after, “I have at last emerged not indeed with the anticipated joy with which I began [diving] into the Crucibles of Nature, but burnt and smoking, dissatisfied, tired.”

  His conclusion was glaringly blunt. “When the central density is high enough … ,” wrote Chandra, “the configurations then would have such small radii they would cease to have any practical importance in astrophysics.” Stars were not expected to act like this. Sir Arthur Eddington was not pleased at all by this news and, during a discussion of Chandrasekhar’s idea of drastic stellar collapse at the 11 January 1935 meeting of the Royal Astronomical Society in London, made the infamous declaration (so often quoted) that “there should be a law of Nature to prevent a star from behaving in this absurd way!” The audience howled in laughter.

  Having just made his presentation to the society, which had been greeted with polite applause, Chandra was horrified to hear this cutting response from Eddington and was mortified by the audience’s response. Chandra had been consulting Eddington for weeks as he carried out his computations, and the great man hadn’t mentioned one word of disapproval. He had even helped Chandra get his needed calculator. It appears that Eddington ignobly waited for a public forum to pounce on Chandra’s results, turning it into one of the most notorious intellectual duels in the history of astrophysics.

  Eddington had one overwhelming gripe: he thought it was wrong to mix special relativity with quantum mechanics, at least in the way that Chandra handled it for white dwarf stars. “I do not know whether I shall escape from this meeting alive,” Eddington told the astronomers, “but the point … is that there is no such thing as relativistic degeneracy. … I do not regard the offspring of such a union as born in lawful wedlock.” In a strident article in the Monthly Notices of the Royal Astronomical Society later that same year, Eddington continued to call it “an unholy alliance.” He simply didn’t trust Chandra’s particular approach. Eddington had displayed such brilliance in the field of astrophysics for so long, especially in setting up the standard model of a star (one of twentieth-century astronomy’s greatest accomplishments), that he couldn’t imagine being wrong. With his academic tweeds, upright posture, and a prim pince-nez clipped on his nose, this noted astrophysicist appeared the very personification of that British pride.

  Eddington’s forthright response at the astronomical meeting was not unusual, though. He was always ready for a good intellectual rumble from time to time. To him, it was the way science got done. Chandra was not alone in his distress; many others had been slashed by Eddington’s rapier wit over the years. But why didn’t others at the society that fateful evening come to Chandra’s defense? Part of the problem was the difficulty of the math and physics in Chandrasekhar’s work; few were as familiar with stellar theories (not to mention quantum mechanics or special relativity) as Chandra was to back him up. Eddington was the world’s expert on the structure and luminosity of stars. Surely he must be right, these bystanders assumed, and Chandra wrong. Others, while supportive of the young theorist’s work, were fearful of openly criticizing Eddington, the most heralded astrophysicist of his era. Even when key astrophysicists within a few years came to recognize Eddington’s error, admitting this to Chandra in private, these scientists continued to keep quiet in public, not wishing to disgrace the high priest of astronomy. Many counseled Chandra to keep any rebuttals to himself. Chandra was very bitter over this lack of support from his peers.

  Given Eddington’s renowned expertise on stars, it’s puzzling that he was not leading the way to new astrophysics. He was a world expert on relativity and comfortable with the application of quantum mechanics in other arenas. In fact, he had earlier supported some of Stoner’s findings on the maximum limit of white dwarfs, communicating them to the Monthly Notices of the Royal Astronomical Society. Why was Eddington now so vehement in keeping relativity and quantum mechanics apart in this case? It’s possible that he was simply overwhelmed by the psychological factor—the preposterous notion that matter could somehow be crushed to oblivion. Where was all that matter going? By then fifty-two years of age and educated during an era when the known universe had been far simpler, Eddington was absolutely certain that nature didn’t behave that way. For him it defied common sense. He acted as if he could smash Chandra’s conclusion through a sheer act of will, ignoring any physics not to his liking. According to British science historian Arthur Miller, Eddington was mainly bullying Chandra to protect a fanciful mathematical scheme he had been working on for eight years, a che
rished (and ultimately foolish) project whose aim was to naturally derive both the physical constants of nature and the number of particles in the universe. Chandra’s finding put all his hard-won work into jeopardy. Eddington’s unified theory didn’t work if relativistic degeneracy were true.

  So, it’s not surprising that Eddington remained adamant in his opposition. In a 1936 address at Harvard University, he continued to call Chandra’s white dwarf limit “stellar buffoonery.” Chandra, ever the gentleman, faced the censure with stoic grace. In those days, says Canadian physicist Werner Israel, “debates were a sport, like cricket. Afterwards, you repaired to the Common Room and shared a glass of port.” Agreeing to disagree, the two managed to maintain cordial relations, continuing to take tea, attend sports events, and go on bike rides together. Certain his analysis was correct, Chandra figured time would settle the issue in his favor. So, he was excruciatingly patient, though inwardly dismayed at what astronomers were thinking of him at the time. “They considered me as a sort of Don Quixote trying to kill Eddington,” he said some forty years later. “As you can imagine, it was a very discouraging experience for me—to find myself in a controversy with the leading figure of astronomy.”

  To be ridiculed by one of England’s towering figures was a scientific humiliation and setback for the young investigator, and it took more than twenty years before the “Chandrasekhar limit,” the highest possible mass of a white dwarf star, became a fundamental parameter in astrophysics textbooks. A Nobel Prize for Chandra followed (much later) in 1983.

  There was a downside to all the machinations that transpired in the 1930s: with Chandra’s confidence decidedly shaken, he abandoned the topic for a couple of decades, eventually immigrating to America, where scientists were more receptive to his ideas. There, at the Yerkes Observatory and the University of Chicago, he proceeded to work on other astrophysical problems. “I had to make up my mind as to what to do. Should I go on the rest of my life fighting?” Chandra later recalled. “After all I was in my middle twenties at that time. I foresaw for myself some thirty to forty years of scientific work, and I simply did not think it was productive to constantly harp on something which was done.” Though Chandra displayed a public equanimity regarding this tempest, privately Eddington’s criticism stung sharply.

  Eddington, it turned out, was simply wrong. Nature did not provide a safety net against stellar collapse. The young Chandra never ventured to guess exactly what would happen to a white dwarf star that ventured past 1.4 solar masses. Conservative by nature, he was never keen on speculation. But he did open the door wide for other theorists to contemplate the existence of neutron stars and black holes.

  Meanwhile, we can mull over the “what if” in this tale: If Eddington had been Chandra’s champion rather than foil, would astronomers have accepted the possibility of black holes faster? Not likely, says Israel, who has deeply examined the scientific temper of these times. “In 1935,” he writes, “the astronomical community was not yet ready to ‘buy’ the idea of gravitational collapse, not even if a master salesman like Eddington had been ready to exert all of his persuasion.” In this prewar era, astronomers were fairly old-fashioned. Few were trained or even interested in applying the new physics—relativity and quantum mechanics—to astrophysical problems. Many didn’t think relativity was even a part of physics but more a branch of mathematics.

  If a new law of physics didn’t stop a singularity from forming, astronomers at this point were confident that other forces would come into play. Stellar physics was still a relatively young field with lots of unknowns. Many just figured that massive stars experienced a vast weight reduction, ejecting enough of their matter over time that each and every one ultimately fell below the critical 1.4-solar-mass limit, where they could safely die as white dwarf stars. Even Chandra admitted he leaned toward this view for a time.

  But this was simply a nice “just-so” story—a convenient dodge—that only for a time kept astronomers from having to face the unimaginable.

  5

  I’ll Show Those Bastards

  Throughout the Milky Way galaxy, there are multiple star systems where two or more stars orbit one another, just the way the Moon circles the Earth. And if one of those stars happens to be a white dwarf, interesting things can happen—as on the night of 29 August 1975.

  As twilight settled over Japan that day, high-school senior Kentaro Osada, an amateur astronomer who regularly scanned the heavens in his free time, noticed that the northern constellation Cygnus the Swan had a new star in its tail, a pinpoint of light that hadn’t been there before and whose luminosity would soon rival the constellation’s brightest star, Deneb. Within hours, a slew of other amateur and professional astronomers wired or phoned news of the appearance to the Central Bureau for Astronomical Telegrams in Cambridge, Massachusetts, the official clearinghouse for new celestial sightings.

  What they were all witnessing was a nova, the name given to the event by ancient astronomers in their mistaken belief that the heavens had created a brand-new star. The appearance of a nova in the sky more than two thousand years ago inspired the Greek astronomer Hipparchus to prepare the first serious catalog of the stars as seen from the Western world. By the mid-nineteenth century, there were a number of quaint theories about a nova’s origin, including swarms of meteors colliding with one another or even a star encountering a cloud of cosmic material and heated to superluminal brightness by the friction as it passed through. But what Osada and others were actually witnessing that night was a stellar outburst—a star that suddenly erupts into startling brilliance then slowly fades back to its normal brightness.

  V1500 Cygni, as the 1975 nova is now officially labeled, involved a white dwarf star and its close companion, a small red star—a binary system located roughly six thousand light-years away. Because the two were such intimate neighbors, the intense gravitational field of the white dwarf was able to pull gas away from the red star, which then formed a swirling disk of matter around the dwarf. Over time, some of this material reached the surface of the dwarf, wrapping the entire orb in a thin blanket of hydrogen. Compressed and heated by gravity, the layer suddenly ignited, engulfing the white dwarf in a monstrous thermonuclear blast. The nova was born. V1500 Cygni’s luminosity swiftly increased by a factor of one hundred million, making it one of the brightest novae in the twentieth century, seen for days.

  Yet, despite such a violent explosion, the system remains intact. Nova Cygni might reappear in ten thousand or more years, after the system’s thief, the white dwarf, steals another layer of fusible hydrogen from its mate. That is the most common form of nova in the heavens. Each year about thirty white dwarfs, sprinkled throughout our galaxy, blow off a little “steam” in this manner. “There is something uncanny about the change in the ancient and familiar configurations of a constellation,” said Henry Norris Russell in 1939. “I well recall the impression which my first glimpse of a Nova produced on me. … It was hard to escape the feeling that it was making a noise!” Many other novae are regularly sighted each year in galaxies beyond our own.

  But even before astronomers understood exactly what a nova was, they recognized that there was more than one kind. Along with those “common” novae popping off in the heavens, astronomers began noticing others that were in a class by themselves—novae that were far more luminous and much rarer. Russell floridly described them as a “phenomena of a different order—the most tremendous yet known to the mind of man.” In our own galaxy, they are seen only once every few centuries. The famous Crab Nebula in the constellation Taurus is the remnant of one such burst, an event recorded by Chinese astronomers in the year 1054. Some astronomers called them “giant novae,” others “exceptional novae.” In his native German, Walter Baade at the Mount Wilson Observatory in California referred to them as “Hauptnovae” (chief novae).

  Not as publicly famous as his Mount Wilson colleague Edwin Hubble, who had confirmed the expansion of the universe, Baade was actually the superior obs
ervational astronomer. In 1952 he corrected Hubble’s too-small size of the universe, discovering that it was twice as big and twice as old. Born and educated in Germany, Baade had a hip defect that made him walk with a limp. But this disability allowed the aspiring astronomer to stay out of World War I and focus on learning a host of useful observing techniques during his graduate studies. Baade, according to his colleagues, “saw the mysteries of the universe as the greatest of all detective stories in which he was one of the principal sleuths.”

  Walter Baade (Courtesy of the Huntington Library, San Marino, California)

  Obtaining a job at the Hamburg Observatory after earning his doctoral degree, Baade got his first look at one of those superbright, rare novae in 1921, the sudden flare-up occurring in a little spiral galaxy called NGC 2608. He was immediately hooked and regularly photographed the nova until it faded away the following year. It was Baade who confirmed that such exceptional novae were stupendously more energetic than the more common type. Indeed, one of these bursts can be as bright as the combined light of an entire galaxy of stars. Given such astounding luminosity, Swedish astronomer Knut Lundmark provided these objects with the name that stuck—supernovae.