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  • It's the 1970s.

  • Sean Connery is still James Bond, fashion is blindingly ugly, and astronomers are working

  • tirelessly to solve the galactic rotation problem.

  • Which is actually a very misleading name, because the problem was

  • that galaxies rotated too well.

  • The stars on the outskirts of galaxies were orbiting much faster than astronomers expected,

  • and they were starting to question what they thought they knew about the laws of physics.

  • Eventually, they realized that they were looking at the first direct evidence for dark matter.

  • And it was an astronomer named Vera Rubin who found it.

  • Rubin was born in 1928 in Philadelphia, Pennsylvania, and she loved to stargaze as a kid, she was

  • especially fascinated by how the stars would move through the sky overnight.

  • Her father, who was an electrical engineer, helped her make a telescope when she was 14,

  • and she started going to meetings for amateur astronomers.

  • In interviews, she used to claim that she faked her way through high school, since she

  • turned every assignment into an excuse to write about astronomy.

  • That passion for the stars carried her to Vassar College in New York, which she chose

  • because one of her awesome astronomer forebears, Maria Mitchell, had taught there.

  • From there, she got a master's degree in astronomy from Cornell, and a PhD from Georgetown.

  • Her master's thesis involved analyzing the movements of more than a hundred galaxies,

  • and her PhD looked into how galaxies are distributed through the universe.

  • Maybe you're starting to sense a theme here: she was really interested in galaxies.

  • After bouncing around between a few different professorships,

  • Rubin landed at the Carnegie Institution in Washington, DC in 1965.

  • It was there that she and fellow astronomer, Kent Ford,

  • turned their attention to how stars orbited the centers of galaxies.

  • Ford had invented a more sensitive kind of spectrometer, a tool that splits up the light

  • detected by a telescope based on its wavelength.

  • Rubin and Ford used it to calculate how fast different parts of galaxies were moving.

  • When they plotted the stars' orbital velocities across a galaxy, they expected to see that

  • the stars close to the center orbited really fast, with orbits getting slower and slower

  • the farther the stars were from the center.

  • Like how in our solar system, Mercury moves much more quickly in its orbit

  • around the Sun than Neptune does.

  • But that's not what they saw.

  • They found that stars on the edges of galaxies

  • were orbiting just as quickly as the stars closer in.

  • It made no sense.

  • The stars on the outskirts of these galaxies were orbiting so fast that the galaxies should

  • have basically flown apart, the mass of all the matter that they could see in each galaxy

  • shouldn't have been enough to hold them together.

  • Now, Rubin and Ford weren't the first people to notice some odd galactic motions.

  • There had been a few isolated observations earlier in the century.

  • For example, in the 1930s, American astronomer Horace Babcock observed that

  • the nearby Andromeda galaxy was spinning way too fast.

  • Jan Oort, the Dutch astronomer who the Oort Cloud is named after, saw something similar

  • with the Spindle Galaxy in the constellation Sextans, and so did a Swiss astronomer named

  • Fritz Zwicky, in some of the galaxies in the Coma galaxy cluster.

  • They came up with a few different explanations for this behavior.

  • Babcock thought it might have to do with light absorption, or maybe that objects on the outskirts

  • of galaxies had some different dynamics that we didn't have the math yet to describe.

  • Oort and Zwicky both independently suggested that there were halos of non-luminous matter

  • around the galaxies, aka dark matter.

  • What Rubin and Ford discovered was that this problem didn't just exist

  • for one or two galaxies at a time.

  • It showed up all across the sky.

  • Babcock, Oort, and Zwicky hadn't found some weird anomalies;

  • they saw specific examples of a widespread phenomenon.

  • Rubin graphed the motions of these galaxies in rotation curves, plotting the velocities

  • of objects from their centers out to their edges.

  • In the 1970s, she gathered and published a huge amount of data, showing clearly and incontrovertibly

  • that the galactic rotation problem was typical galactic behavior,

  • and that there was some kind of unexplained physics at work.

  • She also realized that the dark matter hypothesis was consistent

  • with her observations for all these galaxies.

  • If there was a bunch of matter in them that we couldn't detect, that would explain why

  • the galaxies were rotating so fast.

  • After that, astronomers started finding more and more evidence for dark matter, and these

  • days, most astronomers think that 84% of the matter in the universe is dark matter.

  • Rubin died in December 2016 at the age of 88.

  • Through her decades of work on galaxies and dark matter,

  • she laid the foundation for what's now a huge field of research.

  • Astronomers still have no idea what dark matter is, and there are thousands of researchers

  • all over the world trying to figure it out.

  • So, in a lot of ways, Vera Rubin is still contributing to our knowledge of the universe.

  • Thanks for watching this episode of SciShow Space.

  • And for more on dark matter, check out our videoWhat we don't know about dark matter,”

  • which explores some of the possibilities astronomers have considered over the years.

It's the 1970s.

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