For Ada Lovelace Day: Vera Rubin (Shallow Thoughts)

Akkana's Musings on Open Source, Science, and Nature.

Tue, 24 Mar 2009

For Ada Lovelace Day: Vera Rubin

For Ada Lovelace Day I'm honoring Vera Rubin.

In 1948, when she applied to Princeton as an aspiring astronomy grad student, they wouldn't let her in because women weren't allowed. (They finally started admitting women in 1975.) Fortunately, Cornell was more accommodating.

For her thesis, she worked on a project that seemed useful and uncontroversial. She took other people's data on the redshifts of galaxies, and catalogued them to see how fast they were all moving away from us.

Except something unexpected happened. She found that galaxies in one direction weren't moving away as fast as galaxies in the other directions. The universe was supposed to be expanding evenly in all directions -- but that's not what her data showed.

In 1950 she presented her results to a conference of the American Astronomical Society. The results were not promising. Famous astronomers she'd read about but never met stood up in the audience to ridicule her paper and say it couldn't be true. No one would publish her master's thesis. It wasn't a good start to her career. She decided to try to find something less controversial to study.

Her husband finished at Cornell and moved to Washington, D.C.. Rubin and her new baby moved with him, and she enrolled as a PhD student at Georgetown. They had two children by now; her parents watched the kids while she took night classes.

She hooked up with George Gamow at Georgetown. He called her to ask her about her research -- but said they'd have to talk in the lobby, not in his office, because women weren't allowed in the office area of the building.

After Rubin finished her PhD with Gamow in 1954, Her experience trying to present her 1950 paper made her leery of confrontation. She's said, "I wanted a problem that no one would bother me about." Working with Kent Ford at the Carnegie Institute in Washington, she helped design a super-sensitive digital spectrograph, and they set out to make a huge catalog of data on boring "normal" galaxies no one else was looking at. They started with the Andromeda galaxy, M31, the closest large galaxy to us (and the easiest one to see with the naked eye, if you go somewhere away from city lights).

And right away they found something weird. Normally, you'd expect the outer parts of the galaxy to be rotating a lot slower than the inner parts. Think of our solar system: Mercury goes around the sun really fast (a Mercury year is only 88 days), Earth goes not quite as fast, and when you get all the way out to Pluto, it takes 247 years to go around the sun once. It's not just that it has farther to go to make a circuit around the sun; it's that the sun's influence is so weak way out there that Pluto goes a lot slower in its orbit than we do.

Galaxies should be the same way: stars in the center should just whiz around in no time, while stars at the outer edge take forever.

But Rubin and Ford found that Andromeda wasn't like that. When they started looking at the stars farther out, they were all going about the same speed. If anything, the stars at the edge were going a little faster than the stars in the center.

That made no sense. It didn't follow any normal model of gravity or galaxy formation. They published their results in 1970, but no one took them seriously. They decided that maybe something was wrong, or their equipment was faulty. They decided to try studying a simpler problem: just measure the redshift of some faint galaxies and make a catalog of those.

That went well for a while -- except that pretty soon, they ran into the same thing Rubin had discovered as a graduate student back at Cornell. Galaxies in the direction of Pegasus were moving away from us at a different speed from galaxies in other parts of the sky. She and Ford tried again to present that, but the reaction wasn't any more positive this time.

Discouraged, they went back to trying to measure galaxy rotation, hoping Andromeda had just been a fluke. But every galaxy they studied looked the same as Andromeda, with the stars far out near the edge of the galaxy rotating as fast, or faster, than the stars near the hub.

There were only two possible explanations. Either the law of gravity doesn't work the way we think it does ... or there's a lot more matter inside a galaxy than what we see with a telescope.

When they tried to present this result, no one believed it, so they kept measuring more galaxies, always with the same result.

By 1985, they had enough evidence that people finally started paying attention. As their results got talked about more and taken more seriously, they came up with a name for the extra mass that makes the galaxy rotation flat: "dark matter". Yes, the dark matter you hear about that apparently makes up more than 90% of all matter in the universe. Not a bad discovery for someone who was just trying to lay low and catalogue a lot of data that might be useful to other people! (Rubin's first graduate project, on the rotation of the universe, has also since been vindicated.)

Vera Rubin is still working at the Department of Terrestrial Magnetism. Her intellect, hard work and perseverance are an inspiration, and I salute her on Ada Lovelace Day. (You can read other people's Ada Lovelace Day posts in the Ada Lovelace Day Collection.)

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[ 19:12 Mar 24, 2009    More science/astro | permalink to this entry ]