At that point she chose the problem that became her dissertation: actually simulating the evolution of a galaxy. Setting up a numerical model, she would track its changes in color and brightness over billions of years as the stars within it are born, fiercely radiate, and then inevitably die. It was an ambitious task, as numerical simulations were grueling in this primordial era of computing.
No one before had ever tackled such a problem in great detail. It has been described as “one of the boldest graduate thesis projects ever undertaken.” Tinsley had to set up an initial population of stars and then decide how quickly they would die and how soon new stars would be generated to take their place. And no one yet knew for sure whether a galaxy’s brightness depended more on the collective light emanating from its numerous long-lived, low-mass stars or from its scarcer—but far brighter—short-lived, massive ones. Tinsley constructed her model based on the best theoretical and observational evidence available at the time.
After her dissertation was completed in 1967, she continued to refine her models over the years, each simulation concluding that galaxies can undergo substantial evolution through time, far more than astronomers had previously thought. A young galaxy starts out bright and blue, when its resources of gas to form stars are at their peak, and then gent-ly reddens with age and dims considerably as the stars age and die over the eons.
Some more senior authorities at first took issue with these conclusions, but eventually her findings encouraged observers to start pushing outward with their telescopes to discern her predicted galactic evolution firsthand. As a consequence, Tinsley’s papers began to be cited in dozens of scientific publications. Yale University took notice in 1975 by offering her a professorship, a post she had been unable to secure years earlier (to her great frustration) in either Texas or elsewhere. The woman once regarded in Dallas as “Brian Tinsley’s clever wife, rather than as a scientist in her own right,” according to science historian Joann Eisberg, had proved that people had vastly underestimated her talent.
It didn’t take long for astronomers to get direct confirmation of Tinsley’s theoretical findings. In 1977 astronomers Augustus Oemler Jr. and Harvey Butcher used the 84-inch (2.1-meter) telescope on Kitt Peak in southern Arizona to analyze the light emanating from two galaxy clusters, now known to be situated some five billion light-years away (hence five billion years back in time). What they saw matched Tinsley’s prediction: the galaxies in both clusters were radiating more blue light than the more reddish clusters near us today, likely because there were more blue, energetic galaxies in those clusters than the clusters near us today. No longer mere markers, distant galaxies were now viewed as fascinating and evolving cosmic creatures worthy of study all on their own.
A Hubble Space Telescope photo of galaxy cluster
CL0024+1654, earlier studied by Augustus Oemler
and Harvey Butcher in 1977 to prove galaxy evolution.
(NASA/ESA/H. Lee & H. Ford [Johns Hopkins])
All those efforts ushered in a new era in extragalactic research. Gradually Hubble’s “shadows” began to disappear as new and improved instrumentation allowed the early universe to come into better focus. Faraway galaxies that had been smudges in Hubble’s day are being viewed today with impressive clarity. And what astronomers are seeing is that galaxies over time can exhibit diverse personalities. Some do move serenely through the cosmos, evolving internally as Tinsley calculated, but astronomers now know that many can also change more recklessly. Galaxies may collide, merge, sideswipe one another, or gobble up unwitting passersby. The resultant galaxy-wide temblors often trigger the birth of millions of stars. It is a wondrously invigorating picture of extragalactic affairs, in which galaxies evolve, either dimming or brightening as they age, owing to outside influences.
Sadly, Beatrice Tinsley witnessed very little of the new era she inspired. In 1978 a lesion on her leg was diagnosed as melanoma, a malignant skin cancer. While continuing to teach and carry out research, she underwent extensive radiation and chemotherapy, but ultimately the treatments were unsuccessful. She died in March 1981 at the age of forty. Writing in Physics Today a few months later, Sandra Faber of the University of California, Santa Cruz, observed that Tinsley had “changed the course of cosmological studies.”
Two weeks before her death, while hospitalized in the Yale infirmary, Tinsley submitted her last scientific paper to the Astrophysical Journal. No longer able to use her right hand, she had written it with her left. The article advanced her work on galaxy evolution and was published the following November without revision by the editors.
CHAPTER THIRTEEN
Stuff of the Heavens
How light taught astronomers what the universe is made of
IN 1999 NASA launched a spacecraft called Stardust into the heavens to capture just what its name suggested: matter from outer space that likely originated from long-dead stars, whose remnants provided the material out of which our solar system formed.
In its years-long journey, eventually covering billions of miles as it orbited the Sun, Stardust flew through a stream of interstellar dust, as well as the coma of Comet Wild 2, collecting specks of matter onto its tennis-racket-wide aerogel collector. In 2006 the probe returned to Earth’s vicinity and ejected its precious cargo. Safely nestled in a special capsule, the payload landed in Utah’s Great Salt Lake Desert in the dead of night. Transported to NASA’s Johnson Space Center in Houston, Texas, this cosmic treasure—tens of thousands of microscopic and submicroscopic grains—has been under close scrutiny ever since.
One of the most startling revelations of the dust’s analysis was the discovery of glycine, the smallest of the twenty amino acids that serve as vital building blocks for our body’s proteins. “The significance of this discovery is that comets must have delivered at least one amino acid to our planet before it had life,” said Stardust principal investigator Don Brownlee. Other researchers have found nucleic acids, components of DNA and RNA, in meteorites. It’s further confirmation that “we are made of starstuff,” as Carl Sagan so famously described it in his book Cosmos.
That we have such an intimate connection to the cosmos is actually a relatively new revelation. For most of history, astronomers could not be sure that the stuff of the heavens was anything at all like the stuff on Earth. And since outer space was so inaccessible, they figured an answer would be forever out of their reach. The French philosopher Auguste Comte was so confident in this judgment that in 1835 he boldly asserted that “we would never know how to study by any means [the stars’ and planets’] chemical composition, or their mineralogical structure.” That declaration is one of the most infamous misstatements in the history of science. What Comte did not anticipate was the development of new techniques that—in less than three decades—would sweep away his ill-timed conclusion.
The turnabout primarily happened when Gustav Kirchhoff, a professor of physics at the University of Heidelberg, and chemist Robert Bunsen, creator of the famous laboratory burner, teamed up in 1859 and demonstrated how to identify substances by the specific colors of light they emit during chemical reactions or when burning. Whenever energized and viewed through a spectroscope, each element could be recognized by a unique set of colored lines it displayed.
The spectrometer used by Gustav Kirchhoff and Robert Bunsen.
(From Annalen der Physik und der Chemie, 1860)
Soon the two collaborators realized that such spectral fingerprints could be effectively studied whether the light originated from a distance of one foot within a laboratory or from millions of miles away. That insight may have been prompted by a fire that erupted in the nearby city of Mannheim and was visible across the Rhine river plain from their laboratory window. Upon directing their spectroscope at the flames, Kirchhoff and Bunsen discerned the strong green emission of barium in the roaring blaze, as well as the distinctive red signature of strontium. Sometime later, while they were strolling together through the wooded hills near Heidelberg, Bunsen wondered
if they could analyze the Sun’s light in a comparable fashion. “But people would say we must have gone mad to dream of such a thing,” he declared.
Kirchhoff, though, had no such qualms. By 1861 he had turned his spectroscope to the heavens and identified a number of elements in the Sun’s atmosphere, including sodium, magnesium, calcium, chromium, iron, nickel, copper, zinc, and barium. Within a few years, other astronomers, such as Angelo Secchi in Italy and William Huggins in En-gland, reported finding similar elements in such distant stars as Aldebaran, Betelgeuse, and Sirius. Here was definitive proof that the chemical elements of the Earth were indeed identical to those of the cosmos. The long-standing Aristotelian belief that celestial matter was somehow different from the terrestrial elements was abolished once and for all.
At the top, a continuous spectrum that runs from violet (left) to red (right). Below that, the specific spectral “fingerprints” of sodium (Na), hydrogen (H), calcium (Ca), and mercury (Hg).
(OpenStax, Chemistry. OpenStax CNX, https://opentextbc.ca/chemistry/. June 20, 2016. Copyright 2016 by Rice University. License at https://creativecommons.org/licenses/by/4.0)
Huggins, for one, was elated by these discoveries and couldn’t help but speculate on what this implied. In 1864 he and his collaborator, W. Allen Miller, wrote, “It is remarkable that the elements most widely diffused through the host of stars are some of those most closely connected with the constitution of the living organisms of our globe . . . that at least the brighter stars are, like our sun, upholding and energizing centres of systems of worlds adapted to be the abode of living beings.”
It wasn’t the first time that scholars speculated about life on extrasolar planets, but the new astrochemical data now made it more than a theoretical fantasy.
A century later, some researchers became even more ambitious. In 1955, physicist Charles H. Townes, who would later win a Nobel Prize for the invention of the maser (the microwave precursor to the laser, which emits electromagnetic radiation at higher-frequency, visible wavelengths), was invited to address an international symposium on radio astronomy in England. His topic: the possibility of detecting celestial substances, other than simple elements, via their radio emissions. Townes, a renowned molecular spectroscopist, suggested that elements were likely linking up and forming actual molecules out in space—molecules that emitted intense radio waves. Among the candidates he named were carbon monoxide (CO, the dangerous stuff of car exhaust), ammonia (NH3), water (H2O), and the hydroxyl radical (OH, the oxygen-hydrogen combination that distinguishes all alcohols and is important in atmospheric chemistry).
The response to Townes’s talk was tepid, however. Most astronomers at the time were convinced that such molecules were too rare to seek out. Optical astronomers had already recognized a few molecular species in space, such as the methylidyne and cyanide radicals (CH and CN), but theorists were sure that, once formed, such molecules quickly got destroyed by ultraviolet and cosmic rays. Why devote precious radio telescope time to tracking scarce specimens, which everyone assumed were unimportant to astronomical processes? One of Townes’s colleagues cautioned him that such a search would be “hopeless.”
Fortunately, a few MIT radio astronomers didn’t heed those warnings and looked anyway. In 1963 they found hydroxyl radicals screaming out at a frequency of 1,667 megahertz in the supernova remnant Cassiopeia A. Five years later, Townes himself, along with coworkers at the University of California at Berkeley, recorded the radio cries of both ammonia and water molecules in the galactic center.
A race quickly ensued to snare the next new cosmic molecules. By 1973 nearly thirty were identified; the total today is more than 150—from acetone and hydrogen cyanide to formaldehyde, methane, and nitrous oxide (laughing gas). Astronomers handed out cases of liquor to settle bets once ethyl alcohol was detected in 1974. It’s been estimated that 1022 (that’s one followed by twenty-two zeros) fifths, at 200 proof, reside in the gas cloud where the alcohol was first detected. Of course, the molecules are spread out so thinly in space that you’d have to distill a volume as big as the planet Jupiter to get one stiff drink.
These assorted molecules barely register as pollutants in our galaxy. Only one molecule of ammonia, for example, forms for every 30 million molecules of hydrogen. Yet scarce as these molecules are, their strong radio signals allow astronomers to better map both the Milky Way and the universe.
Hydrogen peroxide, the hair-bleaching agent, was uncovered just several years ago (who knew the cosmos secretly desired to be a blonde?). Using a submillimeter-radio-wave telescope perched on a high desert plateau in the Chilean Andes, an international team of astronomers found traces of the chemical in a dense cloud of gas and dust near the star Rho Ophiuchi, some four hundred light-years distant. Hydrogen peroxide is formed when two hydrogen atoms link up with two oxygen atoms (H2O2). Both elements are critical for life as we know it. Moreover, take just one oxygen atom out of hydrogen peroxide and you get water (H2O). So, further study of hydrogen peroxide’s chemistry out in deep space may help astronomers better understand the formation of water in the universe.
Molecule by molecule—from water to glycine—astronomers are proving that the foundations for life on Earth may have been put into place before our planet even formed nearly five billion years ago.
CHAPTER FOURTEEN
Recipe for the Stars
When a graduate student discovered abundant
hydrogen in stellar spectra, she was bullied
into suppressing her results
THE resolve to pursue science was never an easy choice for a young girl in the Edwardian age. Yet one could, by dint of talent, drive, and the careful choice of one’s parents and social class, overcome the more blatant barriers to a scientific education. Cecilia Helena Payne, in her later years as an astronomer at the Harvard College Observatory, could point to her mild childhood confrontation with the female stereotype gently enforced by the administration of the church school she attended in London. The female principal told her that she would be prostituting her gifts by embarking on a scientific career. But Payne, born in 1900 in Wendover, England, was descended from a family of scholars and historians, and she eagerly unearthed books on botany, chemistry, and physics in the extensive library at her family home. Her father, a barrister, died when she was four, but her mother, an accomplished musician, carefully guided Payne’s education. A simple move to a new and more modern school enabled her to immerse herself in scientific studies.
Payne flourished at the new school and became enchanted by the prospect of life as a scientist. “I knew, as I had always known,” she confessed much later in her autobiography, The Dyer’s Hand, “that I wanted to be a scientist [but] was seized with panic at the thought that everything might be found out before I was old enough to begin!” Of a room set aside for science instruction, she once recalled: “The chemicals were ranged in bottles round the walls. I used to steal up there by myself . . . and sit conducting a little worship service of my own, adoring the chemical elements. Here were the warp and woof of the world.”
Without much ado Payne stayed the scientific course in high school, and in the autumn of 1919, shortly after World War I ended, she entered Newnham College at the University of Cambridge.
Payne’s arrival at Cambridge as an undergraduate coincided with a tremendous upheaval in the understanding of the physical world, when the physics community was reeling from the startling new discoveries thrust upon it. Until the end of the nineteenth century, scholars generally had thought of the universe as a smooth-running clock, and the science of the day was essentially guided by the same principle. The success of Newton’s equations of motion had led to a smug assurance that every phenomenon in the cosmos could ultimately be explained mechanically. But nature was not following that script, and things quickly went awry when theorists tried to apply the mechanistic laws of classical physics to the workings of the atom.
For several decades astronomers had been identifying elements in the he
avens by comparing their spectral emissions and absorptions with those of glowing gases in the laboratory. The mechanism that gave rise to the light, however, was a complete mystery. Then, in 1913, the Danish physicist Niels Bohr deduced that an atomic spectrum is generated as the electrons in an atom jump from one orbit to another, emitting or absorbing bursts of light along the way. That theory enabled Bohr to calculate the specific colors of light that should be absorbed or emitted by hydrogen, corresponding to the difference in energy between a high electron orbit and a lower one in that atom. Bohr’s predictions matched the observed spectrum of hydrogen almost perfectly. On hearing the news, Einstein is said to have remarked, “Then this is one of the greatest discoveries ever made.”
Payne had the wit and tenacity to become one of the first astronomers to apply the new laws of atomic physics to astronomical bodies. In the course of her painstaking thesis calculations, which drew heavily on the new physics, she uncovered the first hint that hydrogen, the simplest element, is the most abundant substance in the universe. The reverberations of that plain fact still echo in astronomy. Here is the fuel for a star’s persistent burning; here is the gaseous tracer that enables radio astronomers to probe a dark, long-hidden universe; here is the remnant debris from the first few minutes of creation. Payne’s discovery did no less than change the face of the material cosmos.
And yet Payne’s name (and equally, her married name, Payne-Gaposchkin) is missing from most astronomy books. One can debate the point—for the evidence is not unambiguous—but her failure to gain the very first rank among astronomers seems to have been caused by the forces of sexual inequality. At the last minute, pressured by her more conservative superiors, she virtually retracted her discovery of stellar hydrogen and published a statement far less definitive than what she actually believed. Her findings were so radical, so different, that she was pushed into softening her thesis. Ironically, the professor who most influenced her to back down eventually confirmed her original suspicions and published the seminal paper on the hydrogen makeup of the stars. Payne has been described as the most eminent woman astronomer of all time. Her doctoral degree was the first ever granted to a student at the Harvard College Observatory (the university’s physics department had refused to accept a woman candidate). But her failure to achieve recognition for one of the most important advances in astrophysics tells much about the pressures on women scientists as they make their way in a man’s world.
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