Cecilia Payne defends her hydrogen-stellar thesis at Harvard

Some discoveries arrive not by the slow accumulation of proof but as a single calculation, set down by a young hand at a desk, that contradicts the consensus of an entire generation of older men. The figure on the page is unmistakable. What follows is not science but procedure: how the discoverer, knowing what she has found, decides what she may be permitted to say.

THE STUDENT FROM NEWNHAM

Cecilia Helena Payne was born at Wendover in Buckinghamshire on 10 May 1900, daughter of the barrister Edward John Payne and Emma Pertz of the Prussian-German Pertz family. She read for the natural sciences tripos at Newnham College, Cambridge, sat under Rutherford in the Cavendish and heard Eddington lecture on the relativity expedition to Príncipe, and took her tripos in 1923. Cambridge would not confer degrees on women. Eddington, who had seen what she could do with a stellar spectrum, arranged a fellowship that carried her in October 1923 across the Atlantic to the Harvard College Observatory at 60 Garden Street, Cambridge, Massachusetts, where Harlow Shapley was assembling a graduate programme and where, in the brick attics of the Observatory, half a million glass photographic plates of stellar spectra waited to be read. She was twenty-three years old. She read them.

THE PLATES

The work of the next eighteen months was the patient measurement of spectral lines on plate after plate, the matching of those lines against Meghnad Saha's recent ionisation equation, the calculation of what temperatures and what abundances would have to obtain in the reversing layer of a star for the observed line strengths to be produced. Saha's equation was new; almost no one in America had yet thought to push it through a quarter of a million stellar lines. The orthodoxy, inherited from Henry Rowland's solar work of the 1890s and codified by Russell himself, held that the Sun and the stars were composed in roughly the proportions of the Earth's crust: iron, silicon, magnesium, with hydrogen a trace. The plates, run through Saha, said otherwise. They said hydrogen by a factor of a million. They said helium next. They said the rocky elements were the trace.

THE LETTER FROM PRINCETON

She wrote up the calculation through the winter of 1924-25. Four hundred and fifteen pages, typed; the title, Stellar Atmospheres: A Contribution to the Observational Study of High Temperature in the Reversing Layers of Stars. Shapley sent the draft to Henry Norris Russell at Princeton for external review, as was the custom: Russell was the dean of American astrophysics, the man whose diagram every student of the stars carried in his head. Russell's letter came back on 14 January 1925. He praised the work in general and then arrived at the abundance calculation. It was, he wrote, clearly impossible. No theory of stellar structure could accommodate it. He suggested, in the careful tone of an older man advising a younger one against the ruin of her career, that she insert into the conclusion a sentence to the effect that the hydrogen and helium numbers were spurious, an artefact of the method. She should publish the rest. The abundance result she should withdraw.

THE OFFICE AT 60 GARDEN STREET

An afternoon in April 1925, in her office at the Observatory, the eastern window giving onto the Common where the elms were just coming into leaf. The typescript on the desk; the conclusion at page three hundred and eighty-eight; the letter from Princeton beside it. She is twenty-five. She knows what the plates show. She knows what Saha's equation does to the line strengths. She knows that Russell does not yet, in January 1925, possess any calculation that contradicts hers; he possesses only the conviction, settled and authoritative and shared by every senior man in the discipline, that stars are made of the same stuff as the ground under his feet at Princeton. The conviction has no equation behind it. Hers has. To take the doctorate she must write a sentence she knows to be false; to refuse the sentence is to be told, by the only external reviewer whose word the department will accept, that the thesis is not a thesis. She thinks of Eddington, who would have stood by the calculation; Eddington is in Cambridge, three thousand miles away, and is not on her committee. She thinks of the half million plates in the attics above her, which will not be read again in her lifetime if she is sent away from the Observatory. She thinks, in the older language she had learned at St Paul's Girls', of the difference between a thing said and a thing known, and that the literature is the place where things said live but is not the place where things known are destroyed. The result is in the body of the thesis. The result is in the tables. A sentence in the conclusion will not remove it; a sentence in the conclusion will only let the thesis through the door. Other readers will come to the tables. The plates will still be in the attic. Saha's equation will still hold. She takes up her pen and inserts, on page 388, the sentence Russell has asked for: that the enormous abundance derived for these elements in the stellar atmosphere is almost certainly not real. Then she submits.

THE DEGREE

She lodged the thesis with the Harvard astronomy department on 9 May 1925, sat the oral on 15 May, and on 18 June was awarded the doctorate in astronomy by Radcliffe College, which conferred the degrees Harvard would not yet confer on its women graduates. It was the first PhD in astronomy ever granted by Radcliffe, and effectively the first awarded to a woman in the field at any American university. Otto Struve, reading the printed monograph the following year, called it undoubtedly the most brilliant PhD thesis ever written in astronomy. The qualifying sentence sat on page 388 like a stone placed across a spring. The water went around it.

PRINCETON, FEBRUARY 1929

Four years passed. In them, Albrecht Unsöld at Kiel and William McCrea at Edinburgh, working from the published thesis, found independent reasons to take the hydrogen abundance seriously. Russell himself, at Princeton, reworked the solar reversing-layer problem by a different method, the analysis of the Fraunhofer line intensities against the curve of growth, and arrived in 1929 at the same conclusion Payne had reached in 1925: that hydrogen dominates by an enormous margin, that helium is second, that the rocky elements are vanishingly minor. His paper appeared in the Astrophysical Journal for July 1929. He cited Payne's thesis in passing, in a manner that left the discovery, to subsequent readers, attached to his own name. The literature accepted hydrogen-dominance from 1929. It did not, for another forty years, agree on who had first established it.

THE OBSERVATORY

Payne stayed at Harvard. She married the Russian astronomer Sergei Gaposchkin in 1934 and signed her later papers Payne-Gaposchkin. She worked on variable stars, on the structure of the Magellanic Clouds, on the photometric catalogues that were the long unglamorous backbone of mid-century observational astronomy, for a salary entered under the budget line for equipment because Harvard had no category for a woman on the scientific staff. In 1956 she was made full professor, the first woman to hold a Harvard professorship in any faculty, and Chair of the Astronomy Department, the first woman to chair any department at Harvard. She held the chair until 1960 and remained on the Observatory staff until her death in 1979. By then the hydrogen-dominance result was the foundation of stellar nucleosynthesis, of cosmology, of the Big Bang itself: every calculation of how the elements were forged, of what the universe is made of, began from the abundance she had derived in the attic at 60 Garden Street and had been instructed, at twenty-five, to disown.

The decisive moment in a science is not always the moment of discovery. Sometimes it is the moment after, when the discoverer is asked whether she will let the discovery stand under her own name on the terms offered, or wait, and trust that the result is stronger than the sentence placed across it. Payne waited. The sentence on page 388 of the bound thesis in the Harvard Observatory library is still there, in the typescript she submitted: a single line of disavowal, set into the conclusion in her own hand, around which the twentieth century's understanding of what the stars are made of quietly flowed.