Cecilia Payne and Vera Rubin

Last night I had the great pleasure of singing in the premiere of Jocelyn Hagan’s new multimedia composition, Creation, with my choir, Vox Femina Los Angeles. It is an amazing work of art, and explores creation from the feminine perspective. Hagan dedicated the piece to Cecilia Payne. There is also a movement called “Searching for Dark Matter,” which, of course, for me, brings to mind Vera Rubin. I was honored to be asked to write the program notes about these amazing women, immediately got carried away, and wrote 1000+ words with two figures. I was gently told that was too long and too technical, and so trimmed it down a bit. But I decided to put the whole thing here.

Cecilia Payne-Gaposchkin (May 10, 1900 – December 7, 1979) was born in England, where she studied physics and chemistry at Newnham College in Cambridge University.  She became interested in astronomy in 1919 after hearing Sir Arthur Eddington speak about his 1919 expedition to observe the solar eclipse, where he was able to test Einstein’s Theory of General Relativity.  Although she completed her studies, she was unable to obtain her degree, as Cambridge did not award degrees to women until 1948.  The only career option available to her in England was to become a teacher, so she began to search for fellowships that would allow her to study in the United States. In 1923, she received one to study at Harvard University.  In 1925 she earned her doctorate, becoming the first woman in the United States to receive a PhD in astronomy.

Payne wrote her dissertation on the chemical composition of stars.  We get clues about this from the star’s spectrum, an example of which is shown in Figure 1.  The spectrum is like a chemical fingerprint for a star.  As the light from the center of the star passes through the surface of the star, the atoms in the star’s atmosphere absorb some of the energy in the light. This causes the dark lines that you see in Figure 1.  These lines are called spectral lines.  In the bottom of Figure 1 you can see that some lines are much deeper than others.  We call this the strength of the spectral line—the deeper the spectral line, the stronger it is.

The strength of the spectral line depends on both how much of the atom exists in the star’s atmosphere and the temperature of the star.  This makes it difficult to determine the composition of the star based solely on its spectrum.  As an example, we know that helium lines (which are not seen in the spectrum shown in Figure 1) are only produced at very high temperatures, but that doesn’t mean that other stars don’t have any helium.

For her dissertation, Payne was able to use new advances in atomic physics to solve this problem and determine both the temperature and chemical abundance of stars based solely on their spectrum.  She showed that stars are over 90% hydrogen and the other 10% is primarily helium.  This was in direct contrast to the prevailing theory of the time that the composition of the stars was nearly identical to that of the Earth, which consists primarily of heavier elements.  This was compounded by the fact that helium is only visible in the spectra of the very hottest stars.  Her results were so shocking that she was told to downplay them by other astronomers, including one of her committee members, Henry Norris Russell.  To accommodate him, she included a statement in her dissertation that her results were “almost certainly not real.”  Four years later, Russell came to the same conclusion using a different method, and while he briefly credit Payne for her work, he received most of the credit for the discovery.  It is only recently that Payne has received the credit that she deserves for this groundbreaking work.  Nearly 40 years after she wrote her dissertation, astronomer Otto Struve called it “the most brilliant PhD thesis ever written in astronomy.”   Today, 100 years after she wrote it, that statement still stands.

Similarly to Cecilia Payne, Vera Rubin (July 23, 1928 – December 25, 2016) was denied educational opportunities due to her gender.  She attempted to enroll at Princeton University to pursue her doctorate; however, they did not allow women until 1975.  She ultimately went to Cornell University, where she studied the dynamics of the Milky Way along with the motion of other galaxies.  After receiving her master’s from Cornell, Rubin earned her PhD from Georgetown University.

Like Payne, Rubin was a pioneer for women in astronomy.  During one notable incident, Rubin was observing at Palomar Observatory, which did not have a women’s restroom.  This fact was used to prevent women from spending extended periods of time there.  Rather than cut her time there short, Rubin cut out a little skirt, pasted it on the picture of the man on the restroom, and told them they now had a women’s restroom.

While not the first person to postulate the presence dark matter, Rubin’s observations systematically verified its existence.  She observed many different galaxies and made measurements of the speeds of stars as a function of their distance from the center of the galaxy.  Her observations defied the standard expectation, suggesting that there was significantly more mass outside the center of galaxies than was visible.  Because we cannot observe this extra mass using any standard observational techniques, astronomers call this mass “dark matter.”  Trying to determine what, exactly, dark matter is is an area of active research, and we are no closer to understanding it today than we were at the time of Rubin’s observations.

Although this discovery upended the standard paradigm of astronomy and physics, Rubin was continually overlooked by the Nobel Committee.  Only five women have been awarded the Nobel Prize in physics in the history of the prize, and prizes are not awarded posthumously.  Controversially, in 2019, three years after Rubin’s death, half of the Prize was awarded for “contributions to our understanding of the evolution of the universe and Earth’s place in the cosmos,” including theories of dark matter.  Those theories could never have been developed without the groundbreaking work of Vera Rubin.  Her accomplishments have been recognized today through her inclusion in the American Women Quarters Program. She also has an observatory named after her.

Both Cecilia Payne and Vera Rubin made ground-breaking discoveries in the face of systemic sexism. Although their discoveries revolutionized the field, they were denied proper credit until much later.  Today, we recognize them for the luminaries of the field that they are.