Yet in all this stellar and terrestrial elemental fingerprinting success, there was a puzzling hole right in the heart of the great ordering system of the elements, the periodic table. One element remained elusive, a blank space in the common cosmic chemistry: element number 43. Where we'd find this mysterious element would change not only our understanding of the elements and the stars but also of ourselves.
A STRANGER IN THE STARS
Mount Wilson astronomer Paul Merrill was an unlikely Moses of the Stardust Revolution, bringing down from a mountain a key clue in 1952 that would point the way to the elemental laws of our stellar origins. The thing was, Merrill wasn't looking to change the world. He liked it well enough the way it was. The son of a minister of the Congregational Church, he was active in his Pasadena, California, church community and was a staunch Republican. Daily at lunchtime, from the 1930s to 1950s, he'd leave his Santa Barbara Street office in the white-stuccoed Carnegie Institute and walk past the neighboring arts-and-crafts-style bungalows for the Reyn Restaurant, still located around the corner on Lake Street. Before entering, if the day was clear, he could look up to see Mount Wilson rising into the blue California sky, and then he'd head for his table and its marbled-blue vinyl bench. If it was an odd-numbered year, the waitress would bring a peanut butter sandwich. During even-numbered years, she'd deliver a fried egg sandwich, in which case his tablemate, friend and fellow Mount Wilson astronomer Alfred Joy, would have the peanut butter sandwich.
Merrill's penchant for consistency and detail found its deepest expression in his work. He was, one long-time colleague observed, “a most seriously, serious scientist.” On many afternoons, he'd head up the winding road to Mount Wilson. Many nights, he'd see Edwin Hubble seated at the base of the huge one-hundred-inch-diameter Hooker telescope, imaging distant galaxies as part of his effort to calculate their speeds—an effort that would underpin the big-bang theory. There were no niceties exchanged between the two, such as “Hey, Ed, what's the latest red shift?” Merrill detested Hubble, and the feeling was mutual. Merrill could “cloud over like a summer thunderstorm blackening the Minnesota plains” at the mere mention of Hubble's name. Merrill thought Hubble was a scientific showman, courting media sensationalism around his expanding-universe discovery, and just plain wrong when it came to some of his measurements of the distances to galaxies and the brightness of distant stars.
Fueling this irritation was the fact that Merrill felt underappreciated. He was a spectroscopist, doing what he felt was the most important aspect of modern astronomy—work largely ignored by the media in favor of Hubble's 1929 discovery of the possible expansion of the universe, which had riveted the public imagination like no previous story in science. To add insult to injury, Hubble's measurements of “red shift” in fact depended on spectroscopy. The red shift of light is measured by comparing the location of the Sun's Fraunhofer lines with those of distant objects. If the lines are moved toward the red end of the spectrum, the light is being red shifted.
For all their differences, Merrill and Hubble were both the type of men George Ellery Hale wanted for his observatory. He realized that some astronomers are what their peers derisively call stamp collectors—focused on gathering, sorting, and describing cosmic objects—whereas others are intent on putting the evidence together into a larger story. Hale believed that the key was to combine both types of personalities and the best possible instruments, which he did at Mount Wilson. On the hundred-inch Hooker telescope, Hale installed a spectrometer with unprecedented resolution, inspired by Bunsen and Kirchhoff's insights. In 1919, he hired Merrill, who already as a young man had demonstrated he was a master at using spectroscopy to tease apart light in order to determine what stars are made of, how they're changing, and how they're moving.
During his forty-three-year official career on the staff of the Mount Wilson Observatory, Merrill accumulated what one colleague described as “a truly monumental mass of carefully compiled observational material…. A gold mine of factual information for those who must eventually construct sound physical theories to account for their properties.” In effect, like the emerging paparazzi in the valley below him, Merrill took countless spectrograms of the stars with the hope of being able to gain some understanding of their lives.
If in all else Merrill was a company man, when it came to the stellar company he kept, the astronomer liked the oddballs. He had what a colleague described as a “passionate enthusiasm for the study of those stars whose spectra show deviation from the normal,” the so-called variable S-stars—a parallel subtype of M-stars. Since their discovery, Mira variable stars—named after the largest and brightest variable S-star, Mira—had intrigued astronomers, most notably because they challenged the long-held belief in the unchangeability of stars. Not only do these bright red stars change, growing alternately brighter and then fading as if they were on a cosmic dimmer switch, they do so in a characteristic fashion. Merrill was particularly interested in long-variable stars, those that pulsated over a period of more than one hundred days—such as R Geminorum, a long-period red variable star located between the stick figures in the Gemini constellation. We now know that these S-stars are Sun-like stars in their death throes, having bloated to many times their original size. Their atmospheres periodically pulse in and out, in the star equivalent of menopausal hot flashes.
By early 1952, Merrill was just months from retirement. His wrist joints were so swollen from years of severe arthritis that he had to use both hands just to hold a cup of coffee. Worst of all, he could no longer endure the cold and the physical effort required for observing at the telescope. Then he received a series of eight spectrograms like none that he, or anyone else, had ever seen. The images were some of the first taken using the spectrograph on the new, massive two-hundred-inch Hale Telescope on Mount Palomar, one hundred miles to the southeast. For any astronomer, a bigger telescope is the difference between seeing and not seeing, between knowing and not knowing; and all astronomers knew that the Hale Telescope was arriving as a conquering giant. Waiting for it to come into full operation was like waiting for Christmas morning. During the testing and adjusting of this new world record–holder, Merrill convinced his Carnegie colleague Ira Bowen to take the spectra of eight bright S-type stars. “I am greatly indebted to him for these valuable photographs,” Merrill wrote in the scientific paper that reported his findings.
In his office on Santa Barbara Street, Merrill hunched over the treasured photographs and inspected the complex forest of dark and bright lines that made up the spectrogram. It's not known in which of the eight spectrograms he first saw it—maybe the spectra of R Geminorum; for five hours and five minutes on March 23, 1951, the Hale Telescope had focused on this red giant star in the middle of the Gemini constellation, and the Hale Telescope's spectrograph had captured and sorted thousands of the star's photons. As the world's highest-resolution stellar spectrogram, it was an extraordinarily detailed and complicated spectra—a proverbial forest in which it was difficult to see the trees. Merrill spotted the usual S-star suspects. There were the characteristic absorption lines for zirconium oxide and titanium oxide. There were the well-known emission lines (S-stars are different from most in also having emission lines from excited atoms) for the elements iron, manganese, and silicon. But amid the light fingerprints of these familiar elements was a stranger—absorption lines that Merrill, in almost a half a century of looking, had never seen. Eventually he nailed down the identity of this mysterious stellar element: technetium. It had no business being there, yet technetium would change our view of the cosmos, rather than the other way around. After all, Paul Merrill was a stickler for details, and starlight doesn't lie.
Today, technetium is well known as the primary radioactive element used in nuclear medicine. If you've ever had a heart stress test or breast lymph node imaging, you've been injected with a tiny amount of this radioactive element. Worldwide, it's injected into millions of patients a year, but until 1937 it was a mystery. When the Russia
n chemist Dmitri Mendeleev mapped out the modern version of the periodic table, this ordering system of columns and rows included blank squares—elements predicted by the table's structure but not yet discovered. Almost dead-center on the periodic table, between molybdenum and ruthenium, and kitty-corner to iron and chromium, was a missing tooth in the periodic table's otherwise solid, logical smile. For more than a century, element 43 had evaded detection.
Chemists tried and failed to isolate element 43 from hundreds of minerals. Technetium was so elusive because it is a most unusual element. In 1937, the Italian chemists Emilio Segrè and Carlo Perrier received a parcel in the mail that contained a rare, exotic, and infinitesimal—less than a billionth of a gram—sample of unknown material. Sent by a colleague at the University of California–Berkeley, the material had been produced by a new machine of the nuclear age, a cyclotron. It enabled scientists to smash together atoms at speeds at which nuclear reactions take place. The tiny amount of silvery metal sent by mail had been produced by bombarding molybdenum with deuterium, a variant of hydrogen that contains an additional neutron. But when Segrè and Perrier analyzed their sample, they did not find element 42, molybdenum; instead they became the first to glimpse element 43. And they'd found not only the elusive element 43 but also the first “Frankenstein element”—the first element created by nuclear alchemy. It wasn't until 1949 that they named it technetium, from the Greek tecknetos, for “artificial.” The next year, technetium's light fingerprint was thoroughly documented by scientists at the US National Bureau of Standards.
It was readily apparent why technetium was so difficult to find on Earth. Technetium is the elemental equivalent of an ephemeral flower bloom. Alone among the elements at the heart of the periodic table, it has no stable, nonradioactive form. Today we know of nineteen isotopes, or elemental variants, of technetium, but the majority decay into other elements in days or hours (the reason it's an ideal tool in nuclear medicine, since it readily disappears from the body), while the longest-lasting isotope has a half-life of about four million years. Compare this with uranium, the half-life of which is 4.47 billion years, about the age of the Earth. This means that when technetium is produced, even the longest-lasting isotopes will have disappeared beyond detection in less than ten million years.
In April 1952, Merrill traveled to Washington, DC, for the annual meeting of the National Academy of Sciences, at which he presented a paper titled “Technetium in the Stars.” He ended his remarks by offering three possible ways to interpret his surprising findings. The first two possibilities seemed unlikely: perhaps a stable isotope of technetium exists in stars, one not yet found on Earth—though Merrill knew that the National Bureau of Standards scientists suggested this wasn't the case; or some stars are so young as to still contain detectable levels of technetium, which still required a longer-lived version of technetium. The third possibility, concluded Merrill almost reluctantly, was that “S-stars somehow produce technetium as they go along,” that while he stood there presenting, stars were actually making technetium. After all, what was possible in cyclotrons at Berkeley was perhaps also possible in the stars. Merrill didn't speculate any further. He didn't need to. His audience would have seen the inference: if stars make technetium, an element in the heart of the periodic table, they aren't just balls of fire but factories of the elements. Without intending it, and while never embracing the implications of his historic discovery, the man who eschewed big talk about an expanding universe discovered the key to an evolving one. He set a spark that helped fuel one of the greatest struggles of the Stardust Revolution: the quest for the origin of the elements.
It is a rather interesting coincidence that physically a man is nearly a mean proportional between an atom and a star. It requires about 1027 atoms to make a human body and the material of 1028 human bodies to make an average star.
—Walter Adams, director, Mount Wilson Observatory, 1928
OF STARS AND ATOMS
Two miles down Pasadena's palm-lined roads from the Carnegie Institute and Paul Merrill's former office is a rectangular intellectual enclave that is the other half of George Ellery Hale's revolutionary vision: the California Institute of Technology. Among the squat buildings on the southern edge of Caltech's leafy campus is a windowless, five-story stuccoed edifice, the W. K. Kellogg Radiation Lab. In the midst of the Great Depression, the Caltech Nobel laureate Robert Millikan—the man who'd weighed the ephemeral electron—used his prestige to bend the ear of William K. Kellogg, the great breakfast cereal inventor, industrialist, and philanthropist. Millikan convinced Kellogg to support a new kind of lab at Caltech, one with extremely high-powered machines that would use light and particles to probe the essence of atoms—and that might also be able to treat cancer patients by using high-energy x-rays to kill tumors. Kellogg bit at the idea, in the process unwittingly joining together the realms of breakfast cereal and the deepest secrets of the cosmos.
The Kellogg lab's windowless nature spoke to Hale's vision for Caltech. This lab wasn't like the observatories up the mountain, which looked out. This one looked within. To pierce the mysteries of the biggest objects in the universe—stars—Hale believed it would be necessary to know the nature of the smallest objects—atoms. This was the new age of astrophysics, one that Hale believed was a two-faced chimera: it could be understood as either astronomy or physics, at once immense and minuscule, and both out there and the essence of here.
Entering the lab today through its heavy, rust-edged main door, you find yourself in a world parsed down for high-energy physics research. The hallway walls are spartan cement, broken up periodically by the original wooden doors of professors' offices. Farther along the hallway, past the chained-off doorway with the sign warning “Radiation Hazard,” is the low-ceilinged, bunker-like common area. The room's worn carpet is dotted with tables and a sofa, and the walls are lined with old scientific journals and books. It feels like a museum as much as a workplace. There's the sense of physicists' ghosts chatting intently, still arguing about the results of a particle accelerator experiment from the lab's heyday in the 1950s, when the nuclear physicists here led the world in probing the nature of atoms. Hanging over the kitchenette sink is a framed photo commemorating that glorious time. The man in the black-and-white photo is William Fowler, the physicist whose name is now most intimately linked to the Kellogg lab.
With his neatly trimmed white beard and jovial energy, Fowler would have made a great Santa Claus. In the photo, flanked by a cheering crowd of fellow Caltech staff, students, and spouses, he's holding up a sports jersey emblazoned with the words “Nuclear Alchemist” over a large number “1.” It's October 1983, and Fowler has just been awarded the Nobel Prize in Physics for, as the Nobel committee put it, “his theoretical and experimental studies of the nuclear reactions of importance in the formation of the chemical elements in the universe.” Or, more prosaically, for his role in unraveling one of the greatest natural mysteries of all time: the origin of the elements, the way that stars forge the cosmic alphabet of atoms, from argon to zirconium.
What the photo doesn't reveal is that, for all his public exuberance, Fowler was haunted by the recognition from Stockholm. It had forced him to choose between two great loves. On the one hand was “the lab,” his home and family for almost half a century, where he'd started as a graduate student and was now the venerated patriarch and administrative defender. On the other existed a singular, personal, and scientific friendship—and the truth that he knew it held. To get a glimpse behind Fowler's smiling facade and into the complexity of what he was feeling, you have to walk across the Caltech campus and don cotton gloves in the university's Ivy League–quality archives. There, among the thousands of letters, lecture notes, scientific jottings, and articles that Fowler meticulously kept—including correspondence with a who's who of twentieth-century physicists—is a photocopy of an airmail letter. It's dated November 3, 1983, and is addressed to his friend of thirty years, the renowned British astrophysicist Fred H
oyle.
They'd met in Fowler's Kellogg lab office in 1952, when the brash young Brit, on a visit to Mount Wilson, tracked down Fowler with a preposterous suggestion. Hoyle proposed that carbon, the sixth element in the periodic table and the cornerstone of life, was made in stars. Not only that, but he was sure that Fowler's lab had the atomic tools and the know-how to prove Hoyle's hypothesis. Fowler's colleagues in the room at the time dismissed Hoyle's hypothesis as the rantings of an astronomer way out of his league in atomic physics. After all, by this time the Kellogg lab physicists were second to none in measuring atomic transmutations. Their quantum mechanical calculations showed that there was no way carbon could be forged in stars. Impossible. Nevertheless, whether because of Hoyle's intensity and evident intelligence or due to Fowler's enormous gregariousness and willingness to step into the unknown, Fowler didn't escort Hoyle to the Kellogg lab's heavy steel-doored exit. Instead, he gathered colleagues and started planning a momentous experiment.
Fowler may have recalled this meeting as he sat in the office where the two men had first met and where he wrote to Hoyle after receiving the call from Stockholm:
Dear Fred,
After the initial elation and excitement I have had a heavy heart for two weeks. It is impossible to understand why the prize was not given to you or shared between us. I realize that nothing I can write will help but this personal note to you helps relieve my own feeling of hurt.
The Stardust Revolution Page 6