Cecilia Payne: She Found What Stars Are Made Of

Posted by by Female Obscura

She read the stars right. He made her call it wrong.

In 1925 a twenty-five-year-old graduate student worked out what the universe is made of. She showed that the Sun and the stars are overwhelmingly hydrogen and helium, not iron and rock like the Earth. The most powerful astronomer in America told her she was wrong, and she wrote a line into her own thesis calling the result untrue.

Her name was Cecilia Payne.

The English girl who insisted on physics

Payne was born on 10 May 1900 in Wendover, England. She entered Newnham College at Cambridge in 1919 and forced her way into physics at a time when a woman in the natural sciences was steered toward botany and teaching. In December 1919 she heard Arthur Eddington lecture on the eclipse observations that confirmed Einstein, and she came away, in her own words, done with biology and dedicated to physical science forever.

Cambridge let her sit the examinations. It did not give women degrees. So in 1923 she took a fellowship offered by Harlow Shapley and crossed the Atlantic to the Harvard College Observatory, where half a million glass photographic plates held the light of the stars and a staff of women was employed to read them.

What the plates said

The observatory’s plates recorded stellar spectra, the barcodes of dark lines that each element stamps on starlight. Payne had something almost no astronomer of the day possessed. She had learned the new quantum physics at Cambridge, and she knew Meghnad Saha’s equations linking those spectral lines to temperature and pressure.

She used them to read the plates properly. The strength of a hydrogen line did not measure how much hydrogen a star held. It measured how many hydrogen atoms sat in one particular excited state, and in the Sun’s atmosphere that was roughly one atom in every two hundred million. Correct for that, and the hydrogen did not shrink. It exploded. Payne calculated that hydrogen and helium were not trace ingredients but the overwhelming bulk of every star she measured, and that the stars differed in colour because they differed in temperature, not because they differed in stuff.

She wrote it up in her 1925 doctoral thesis, Stellar Atmospheres. The astronomer Otto Struve later called it the most brilliant PhD thesis ever written in astronomy.

The line she was made to write

The reigning theory said otherwise. The leading astrophysicists of the day, Henry Norris Russell of Princeton foremost among them, held that the Sun’s composition matched the Earth’s crust, heavy elements and all. Russell ran American stellar physics. He was also on the committee judging Payne’s thesis.

He told her the hydrogen abundance was impossible, and he pressed her to say so. In the published thesis the sentence appears, attached to her own correct finding: the enormous abundance derived for hydrogen and helium in the stellar atmosphere is almost certainly not real. She left every calculation standing and disowned the conclusion they pointed to.

This is the mechanism, and it needs stating precisely, because the popular version overstates it. Russell did not steal her work or hide it. Four years later, in a 1929 paper in the Astrophysical Journal, he derived the same result by a different route and wrote plainly that the most important previous determination of the abundance of the elements was Miss Payne’s. The citation is there in black and white.

What happened is quieter and harder to correct. The senior man talked the junior woman into publicly doubting her own right answer, then published the answer under his own name in a venue that carried weight, and the discovery entered the textbooks as Russell’s. For decades the hydrogen Sun was credited to him. The disclaimer she was pressured to write did exactly what a disclaimer does. It moved the authority off her page and onto his.

The abundances were hers

The modern numbers settle the question. The Milky Way runs to roughly 74 percent hydrogen and 24 percent helium by mass, with everything else, all the iron and oxygen and carbon of the older theory, making up the last 2 percent. Payne was right, in 1925, at twenty-five, against the consensus of the field, and she had the calculations to prove it before she was talked out of saying so.

The recognition came slowly and in a different currency. She stayed at Harvard, where advancement to professor was closed to women, and she spent years doing first-rank research in low-paid, unnamed roles. She wrote the standard books. She trained astronomers. Only in 1956 did Harvard make her its first woman full professor, and then the first woman to chair a department, at an institution that still would not admit women as undergraduates.

She died in Cambridge, Massachusetts, on 7 December 1979. Her obituary called her probably the most eminent woman astronomer of all time and said, correctly, that she had demonstrated for the first time what the universe is made of. She had also demonstrated, at the start of it all, how a correct result gets detached from the person who found it. Not by theft. By a single sentence, written under pressure, into her own thesis.

The archive grows. The silence shrinks. Enter the archive.

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