Hydrogen Rules the Universe: Cecilia Payne-Gaposchkin and the Composition of Stars (Women in Science 48)
“You are young, and wrong. You must retract.”
When fresh-faced zeal confronts experience, it usually loses. Scientists who think they’ve solved everything on day one usually find that they’ve merely wandered into a seductive semblance of a solution, the first of many in the years to come, and firmly correcting them is part of the sacred duty of every senior researcher. But what happens when the young person is right, revolutionarily right, and repeatedly revolutionarily right, and just as repeatedly compelled to retract their work?
What happens is Cecilia Payne-Gaposchkin (1900-1979). On at least three separate occasions, she advanced astronomical theories on the basis of overwhelming data, only to back away from them under pressure from her superiors, her insights only being ultimately validated later (often much later), when male researchers came to them independently. In the meantime, she slogged away, overseeing the categorization of over three million stars for a paltry wage in the face of persistent denial of personal advancement.
Born in England to a family of ancient lineage, she was a polymath genius from the first. Her father died when she was only four, but impressed in her a deep love of classical music that translated into a passion for violin playing and orchestral conducting later in life. At school, she studied Latin and Greek, and set about teaching herself French and German, just four of the six (or seven if you count her forays into Icelandic) languages she’d ultimately speak fluently. She wrote poetry, could recite long passages of Shakespearean drama from memory, and generally had all the makings of a prodigiously gifted humanities student, were it not for the fact that she was even better at science and mathematics.
She initially had her heart set on botany, but in college one day she happened to hear a lecture by Eddington about relativity, and something deep clicked. She rushed home and wrote the entire lecture down verbatim from memory (sounds remarkable, but this was something many people could do in the days before we relinquished control of our memory to portable storage devices). There was something in the mathematical sureness of Eddington as against the messy particularities of botany that she found fundamentally compelling, and she switched her course of study accordingly.
Her interest lay in the application of the new discoveries of emerging quantum mechanics to the understanding of stars. This was the late nineteen-teens, when we still didn’t really know what stars were made of, nor did we have the facilities to investigate how the ionization of atoms works at exceedingly high temperatures. From the depths of quantum assumptions, however, some theoretical models were starting to emerge, and one in particular would have a profound impact on Payne. In 1920 Indian astrophysicist Meghnad Saha developed the Saha Equation, which described how temperature and pressure would affect the ionization of atoms.
When you raise the temperature of a gas, the particles start slamming into each other and knocking electrons about, creating gas ions of various charges. Saha’s model made predictions about the frequency of all the different ions you’d find in the resulting plasma. And that’s exactly what Payne, who was interested in using the spectra of stars to determine their composition, needed to explain the seeming chaos of the existing spectral data.
But to do that she’d need a research position, and there simply were none in England to be had for a woman. Everywhere she turned, the advice was the same, “If you want to continue in astronomy, go to America, and especially to Harvard.” And that’s what she did. Harvard was, at the time, the leading astronomical institution in America, if not the world, and it was built almost entirely on the work of women. Here Henrietta Swan Leavitt had discovered the correlation between luminosity and period of Cepheid stars. Here Annie Jump Cannon had personally categorized over a quarter million Southern Hemisphere stars, and Antonia Maury a similar number of Northern stars, their combined work creating the mammoth Henry Draper Catalogue. And it was here that Cecilia Payne would, in just under two years, write the paper considered by many to be the best graduate astronomical paper ever produced.
She arrived in 1923, took over Henrietta Swan Leavitt’s empty desk, and dove into the task of making sense of stellar spectral data. And it was a mess. Each star seemed to have an entirely different story to tell, featuring emission and absorption lines (frequencies of light emitted or swallowed when electrons hop between energy levels) that defied all ready categorization. The reigning assumption was that stars must have elemental compositions similar to those on Earth – why shouldn’t they, after all? If Earth was made from thrown off bits of the sun during its formation, why shouldn’t the two have roughly the same amounts of elements? However, the spectral data seemed to tell a different story, which it was Payne’s fate to unravel.
Applying Saha’s equation, she was able to explain the variations not as indicative of the presence of different elements, but of different ionization rates arising from differences in temperature. As such, she was able to use the spectral data to create temperature scales of the stars in question, which would have been useful enough on its own, but in analyzing the elements that were present, she discovered that hydrogen was over a million times more abundant than predicted by the “stars are like Earth” theory. It was a radical departure from the common wisdom of the day, and both Shapley, Harvard Observatory’s director, and Henry Norris Russell, perhaps the most famous astronomer of his age, put pressure on her to downplay her findings.
She was young, facing down two of the pillars of the astronomical community, both of whom she revered as essentially walking gods, and she did as she was told. In the paper she published, she concluded by saying that her theory about the frequency of hydrogen was probably wrong, and substituted a pet explanation of Russell’s as to the most likely source of the discrepancy. She had been absolutely right, but had backed down before authority, and not until 1928, when Albrecht Unsoeld’s calculations of relative elemental abundances backed up Payne’s original work, would the astronomical community as a whole recognize the value of what she had done as a mere graduate student.
From stellar spectra, Payne moved to a study of the supergiants, and found discrepancies in the data that she believed to be explained by interstellar gas absorption. Light coming from a star, she thought, was hitting clouds of invisible gas on its way to Earth. When gas gets hit with light, it steals the frequencies of color that will allow the electrons of its atoms to jump up a level. The light that makes it through, therefore, is different than the light that went in, and so the colors we see are different than those that originally left the star. Payne argued passionately with Shapley for the existence of a significant interstellar gas effect, but it contradicted one of his own cherished theories, and he pressured her to drop it, so she did. She was, once again, absolutely correct.
There was even a third incident where she was sure that the Stark Effect, in which atomic lines split in the presence of an electromagnetic field, occurred in stellar spectra, and found evidence of it in the helium lines of super-hot stars. She took her results to Shapley. He told her to bury them, and she did. She didn’t publish her data, and so it is Otto Struve who we now think of as the discoverer of this phenomenon, and not Cecilia Payne.
The story just gets sadder. The director of the Observatory wanted Payne to undertake the task of organizing and standardizing all of the data that had been piling up since 1889, and so she had to abandon her work on spectra to undertake the task that had similarly swallowed Swan-Leavitt’s research ambitions during Pickering’s directorship. She did phenomenal work, systematizing upwards of three million stars and discovering troves of new variable stars which opened up whole new fields of study, and she did it while editing all of the Harvard Observatory’s publications, and for pay that was a fraction that of her male counterparts. For years, she wasn’t allowed to teach under her own name, because Harvard’s president refused absolutely to allow women full faculty positions, and when the position of Director opened up, as it did on several occasions during her fifty plus years working there, she was repeatedly and automatically barred from the position.
Why didn’t she go to a different university, one which was amenable to female professors? Europe was out for political reasons, and because their record of letting women work in astronomy was still far less advanced than Harvard’s second classing of them. There were other universities in America she could have gone to, but none of them had the sheer treasure troves of data that Harvard did. She stayed because it was there that she could do the work she loved doing. It was emotionally difficult, and at times subsistence was just barely maintained (she had to pawn her beloved violin one month just to have enough money to eat), but she couldn’t leave it behind because nowhere else had the means of investigating the questions that interested her, and I suspect the university knew this full well, which was why they were in no hurry to bring her salary up to a respectable level.
Time passed. Payne spent her off hours, such as they were, conducting the observatory orchestra, creating art from improbable objects, raising children, and cooking elaborate meals. In short, her leisure hours were busier than most people’s working hours, and her working hours contain contributions to science numbering in the literal millions. Her first paper, after its conclusions had been verified, made her famous, and her subsequent work had a longevity not given to many astronomers. Her citation rate was constant throughout her life, which almost never happens, and dipped only slightly after her death.
She was, and will always be, the first person to announce to the world the stuff of the stars.
FURTHER READING: Payne wrote an autobiography at the very tail end of her life which ranks among the greats of scientific memoir writing. There’s a neat edition of it edited by her daughter, Katherine Haramundanis, that is published by Cambridge and contains four introductory essays, two of which are great, one of which could have stood some editing (perhaps because it is by the editor), and one which rambles charmingly along here and there without any particular notion of Whence. Altogether, it’s a great portrait of early twentieth century astronomy in one of the world’s leading institutions, filled with portrayals of an astounding assortment of women who silently shaped our knowledge of the universe.