The Stardust Revolution

by Jacob Berkowitz

  From Mount Wilson, the Burbidges descended to Caltech with what they'd sought. Combing through the astronomical literature, they'd chosen an old star named HD 46407, a so-called barium star, because of the abundance of the metal barium in its spectrum. The Burbidges carefully measured the abundance of any other heavy elements they believed the star was forming through gradual neutron capture and subsequent beta decay. Many of these are the rare-earth elements—including lanthanum, neodymium, and praseodymium—that today are the essential metallic hearts of our high-tech tools, from smartphones to the batteries in hybrid vehicles. The barium star's light fingerprint showed it was stuffed with these rare earths—up to ten times the amount measured in other stars. The Burbidges had seen with their own eyes what others were describing. For almost a decade, astronomers had begun to see that not all stars had the same percentage of elements heavier than helium, what astronomers refer to collectively as metals. Merrill's detection of technetium had been the smoking gun, and now the Burbidges had a roomful of stellar elemental forensics that all pointed in one direction: stars were changing themselves. They were maturing and, in the process, creating new elements.

  The final piece of the cosmic puzzle came almost as a gift-wrapped Christmas present in the January 1956 issue of Reviews of Modern Physics, in an article titled “Abundances of the Elements.” Here were the latest detailed calculations of cosmic elemental abundances and an updated version of Goldschmidt's chart—the equivalent of a puzzle-box cover against which the four-person stardust team could test their nuclear and stellar calculations to the decimal point. The authors, Hans Suess, a geochemist with the US Geological Survey, and Harold Urey, the father of planetary sciences and cosmochemistry at the University of Chicago, wanted them to do just that. They'd compiled an exhaustive list of elemental abundances from meteorite samples, stellar observations, and terrestrial samples to produce an abundance curve that is the template for today's estimates, all the way from hydrogen, down into the depths of lithium and boron, up through the iron peak, and down into the saw-toothed realm of the heaviest elements. Suess and Urey believed “the abundances of the elements and their isotopes reflected nuclear properties and that matter surrounding us bore signs of representing the ash of a cosmic nuclear fire in which it was created.”

  The Burbidges, Hoyle (who'd recently joined the others at Caltech), and Fowler set to work to prove just that. They worked to match the contours of the jagged line of the elemental abundances to the stellar forces that had shaped it. “Dear Hans,” Fowler wrote on July 10, 1956, to Hans Bethe, his mentor and the man who'd solved the first riddle of what powers stars, “Hoyle, Burbidge and I are currently engaged in showing that the latest abundance curves of Urey and Suess are consistent with all schemes of nuclear cookery.”

  They titled their October 1957 paper in Reviews of Modern Physics simply “Synthesis of the Elements in Stars.” In it they solved a millennia-old mystery, the origin of the elements from arsenic to zirconium and every letter in between. Astrophysicists, however, know it by another name, B2FH—the acronym for the order of the authors, the two Burbidges, Fowler, and Hoyle. For astrophysicists, saying “B2FH” is the equivalent of saying “Magna Carta” or “Rosetta Stone”: the term conjures up much more than a single title offering incremental insight into the heart of Nature. It represents something monumental: a touchstone for a way of understanding the world, whether in relation to democracy, language, or our origins in the stars. B2FH lives up to its billing just in length—at 104 pages, it's a behemoth that speaks more to a grand treatise than a single article, as if the Burbidges, Fowler, and Hoyle couldn't stop themselves in the telling the magnificent story they'd unraveled. Perhaps sensing the paper's import, Fowler, uncharacteristically for the author of a scientific paper, searched for quotes with which to preface it. He landed on another Willy, who wrote in King Lear: “It is the stars, The stars above us, govern our conditions.”

  B2FH created a whole new language, that of the Stardust Revolution: a way of talking about the origin of the elements in stars, of stars as the cauldrons of atomic transmutation. The paper described six different key processes of stellar nucleosynthesis to account for the ninety naturally occurring terrestrial elements from hydrogen to uranium. First, there was hydrogen burning into helium, as described by Hans Bethe. Then, as a large star exhausted its hydrogen, it contracted and heated, and the helium would start its nuclear burn, forming carbon and oxygen. This set the stage for the alpha process, when massive stars' cores burn carbon and oxygen, forming the elements from neon to sulfur. Now the processes bifurcate, depending on a star's ultimate fate. In large stars that form red giants and gradually puff out their atmospheres, ending as carbon-oxygen cinders called white dwarf stars, there's a slow process of neutron capture, dubbed the s-process. The s-process gives new cosmic meaning to the word slow. In these elderly, extinguishing stars, neutrons stream out from the star's core, occasionally on just the right path and with just the right energy to collide with an existing atomic nucleus farther out in the star's shell and merge. Any given atomic nucleus doing a crazed energetic journey in a star captures a neutron about once every ten thousand years. In this geologically slow process of neutron capture and beta decay, atoms all the way up to element 83, bismuth, are forming as you read this.

  Just as the s-process defines slow, the r-process, for rapid, gives new meaning to fast. Here, exploding stars—supernovas—provide the runaway energy and machine-gun spray of neutrons to accomplish in mere seconds what occurs in red giants over tens of millennia. It's as if there were two ways to bake a cake: one that was done just after you closed the oven door; the other that would be eaten by your distant descendants, who'd have created some mythic story to describe the bizarre cake that emerged, unbidden, from the oven. It's the r-process to which we owe the bulk of the world's precious metals, silver, platinum, and gold. From B2FH we know that every gold wedding ring doesn't just bind a couple; through its trillions of gold atoms, each with seventy-nine protons and seventy-nine neutrons, it binds them to an alchemical cosmic blast that took place billions of years ago; that for weeks burned brighter than an entire galaxy of stars; and that, in the time it takes to say “I do,” transmuted an Earth's mass worth of lesser elements into gleaming gold.

  More than just elucidating the origin of the elements, B2FH created the astronomer's periodic table, one that would open previously unthinkable ways of seeing and understanding the cosmos. Like the director's version of a movie, the astronomer's periodic table provides the cosmic backstory. For astronomers, unlike chemists, their periodic table isn't a tool to understand how elements chemically combine. Instead it's a visualization of how these elements were formed. Thus every element is a tracer of its origins. Seen in this way, the periodic table becomes the story of the universe in ninety key symbols, from H for hydrogen to U for uranium. The elements form a kind of cosmic DNA. Each object—whether a speck of cosmic dust, a meteorite, a star, a galaxy, you, or indeed DNA itself—has in its elemental composition the detailed story of its cosmic origins.

  Previous generations of astronomers used stars' light fingerprints to catalog stars, to group them, and to differentiate between them. However, they were stumped when it came to thinking in broader ecological terms of the changing relationships between stars over the billions of years of cosmic time. Until the understanding of stellar nucleosynthesis and the creation of the astronomer's periodic table, this was an intractable problem—there was nowhere to begin, no foothold of information from which to begin to reach for an understanding of cosmic natural history. The astronomer's periodic table changed this.

  NOBEL CONCLUSIONS

  B2FH has stood the test of time. In his 1983 Nobel Prize lecture, “The Quest for the Origin of the Elements,” William Fowler noted that some of the elemental gaps in B2FH were filled in by others in the quarter century since; for example, how the small-element numbers 3, 4, and 5—lithium, beryllium, and boron—are created in interstellar space when
larger atoms are shattered by cosmic radiation. Fowler also filled in another gap. He acknowledged his friend and colleague with precedence of discovery: “The grand concept of nucleosynthesis in stars was first definitively established by Fred Hoyle,” he told the king of Sweden and others gathered for his lecture. Hoyle's former adversary, Gamow, had already long conceded defeat with a biblical-style ditty in which God forgets to create the elements in the big bang: “And so God said: ‘Let there be Hoyle.' And there was Hoyle. And God saw Hoyle and told him to make the elements in any way he pleased.”

  By this time, Fowler had had time to reflect on the cosmic irony of it all. If it was indeed the stars that determine our fates, Hoyle's weren't twinkling but winking ironically. For one, Fowler shared the 1983 Nobel Prize in Physics with Subrahmanyan Chandrasekhar, one of the early supporters of big-bang nucleosynthesis, against which Hoyle had argued. This was a modest irony, compared with the bigger picture. While Hoyle continued to rail against the concept he'd named, his fastidious work in cosmic nucleosynthesis proved to be among the best, most concrete evidence for it. The existing amounts of hydrogen and, more importantly, helium provide tight constraints on the temperature, density, and rate of expansion in the birthing moments of the universe when these elements were cooked up. These primeval abundances were further refined by Hoyle, Fowler, and others with the 1965 discovery of the cosmic microwave background—the remnant birthing sounds of the big bang—which clinched the case of the big bang for most cosmologists.

  When Fowler took the stage in Stockholm that December night, he'd already received Hoyle's response to his letter. “Dear Willy,” Hoyle began in the little more than one-hundred-word reply to his colleague and friend of thirty years, “It has been clear I think to many people that the subject of nucleosynthesis in stars was likely to attract such an award sooner or later. In so far as I have thought about the matter myself, it had seemed to me that the two of us might share the Prize.” The British papers thought the same, and headlines howled at the Nobel injustice. Journalists didn't have to look far for possible reasons the Nobel committee might have overlooked Hoyle. By this time, Sir Fred, always contentious, was well on his way to becoming a scientific pariah. From trumpeting the arrival from outer space of the virus that causes plagues, to the existence of an intelligent cosmic deity, Hoyle had isolated himself to the extent that the Nobel committee might well have shied away from giving him a global podium.

  The experience only pushed Hoyle deeper in that direction. In his 1994 autobiography, Home Is Where the Wind Blows: Chapters from a Cosmologist's Life, Hoyle doesn't mention the Nobel Prize. His account of his scientific journey rings with the barely restrained subtheme of gross misattribution of credit in science, from Darwin getting credit for the earlier work of Alfred Russel Wallace and others, to Cambridge PhD student Jocelyn Bell's earlier snubbing by colleagues and the Nobel committee for her shared discovery of pulsars—rapidly spinning dead stars that emit intense streams of radio waves, blinking on and off like cosmic lighthouses. “The fiction is that credit is awarded in proportion to discovery,” wrote Hoyle, “whereas, in fact, credit is awarded to those who influence the world, whether or not they were the real discoverers.” At other moments, when it came to notions of success, Hoyle had a sense of philosophical resignation that ultimately success didn't really belong to anyone at all. It was all the voice of the cosmos. “Scientific discovery is not really what we think it is,” he wrote, taking a different tack. “What happens is that the Universe programs our brains. The success really belongs to the Universe, not to us, and this has been the way of it throughout human civilization.”

  Indeed, Hoyle knew that he wasn't alone when it came to being overlooked in the attribution of credit for the discovery of stellar nucleosynthesis. “Don't forget Al Cameron,” Geoffrey Burbidge said when I spoke with him two years before his death in 2010. Alastair Cameron was a Canadian nuclear physicist recently appointed as a professor at Iowa State University when he read and was entranced by Paul Merrill's famous 1952 “Technetium in Stars” paper. He beavered away in parallel to Hoyle, Fowler, and the Burbidges (contributing insight into neutron capture that was critical to Hoyle's 1954 paper), and almost single-handedly accomplished the equivalent of B2FH, publishing two seminal papers in the same year, 1957. But since he was working at Canada's Chalk River Nuclear Laboratories, where a government wartime ethos persisted and extended secrecy to nuclear reactions in stars, his research was initially classified, and though it was later published, it remains in the deep shadow of B2FH.

  Whatever else happened, Hoyle, Fowler, the Burbidges, and a grand cast of other astronomers, physicists, chemists, and geologists across three centuries had put together the pieces to solve one of humanity's greatest puzzles—the origin of the elements. They'd traveled on an epic scientific journey that took them into the hearts of stars and way back to the origin of all that is. They'd tied together the periodic table of the elements, atomic physics, and stars into a new story of creation. In the end, they'd done more than any alchemist could dream. They didn't just uncover the Philosopher's Stone, the timeless wisdom of how to transmute elements from one to the other; they'd realized that we walk as the embodiment of this mystery. On Geoffrey Burbidge's death, his colleagues at the journal Annual Reviews in Astronomy and Astrophysics, which he'd edited for thirty-two years, offered this as part of a tribute: “When singer Joni Mitchell said ‘We are stardust,' she was quoting Geoff.”

  For these scientists, after all this searching, the discovery of the origin of the elements wasn't so much an ending as a new beginning. They'd created the astronomer's periodic table, a way of exploring the family history of every atom and larger object in the cosmos. And B2FH had tied the elements to the stars, just as others were working to understand another elemental relationship closer to home—that between the elements and life.

  It is a slightly arresting notion that if you were to pick yourself apart with tweezers, one atom at a time, you would produce a mound of fine atomic dust, none of which had ever been alive but all of which had once been you.

  —Bill Bryson, A Short History of Nearly Everything, 2003

  DARWIN'S GAP

  Y ou'd be hard-pressed to find a group of people with more experience thinking about the nature of life than the dozen or so scientists sitting around the table for the fall 2010 meeting of the Committee on the Origins and Evolution of Life of the US National Academies’ Space Studies Board. The group, assembled at the former summer home of a Wall Street banker on the outskirts of Woods Hole, Massachusetts, runs the gamut of life research. There's a paleontologist who studies the billion-year-old fossils of the Earth's earliest multicellular organisms. There are microbiologists who show slides of wonderfully exotic locales where they've searched for extremophiles—single-celled creatures that make a living where, only decades ago, we thought life couldn't possibly get a foothold: in (not on, or under, but in) Antarctic ice, in sulfuric hot springs, or two miles underground, where, without light or oxygen, bacteria breathe sulfur and eat radioactivity. The meeting includes guests from the Craig Venter Institute, who describe their efforts to create artificial life. Venter made his fame and fortune inventing the technology that underpins all genomics research, including the Human Genome Project. His eponymous institute, which he heads, is leading the effort to make life from scratch. Rounding out the group are NASA scientists involved in looking for life on Mars and Saturn's moons.

  Although its main task is to think about how and where life happens, this session begins with a presentation about how difficult it is to get rid of some undesirable forms of life. Via teleconference, a NASA official explains the challenges of sterilizing robotic spacecraft before their launch to distant locales in the Solar System. NASA's first life-science challenge in missions to the Moon and Mars isn't finding alien life but avoiding the transfer of microscopic stowaways from Earth and thus leaving our own life footprint elsewhere in the Solar System. As a partial fix for this problem,
NASA uses ultraviolet (UV) light in its prelaunch clean rooms to sterilize spacecraft as part of its Planetary Protection Program. In what is perhaps the first case of NASA-driven bacterial evolution, this process has selected for UV-tolerant bacteria. In an effort to kill them, the space agency made them better and stronger. “This is the Earth. We can't keep the bacteria out,” the NASA official complains.

  The day's first lesson: life is tenacious. For most people today, the daunting problem with life isn't to know how it began but how to end it—from homeowners plotting ways to kill dandelions, to NASA engineers trying to rid Deinococcus bacteria from spacecraft—which is what creates the slight cognitive dissonance in the meeting room. This is, after all, the Committee on the Origins and Evolution of Life. Yet, often, the elephant in the room during the discussions is the question not of life and its evolution but of life's very beginnings.