Dark Matter Clues

  • By Michael Rivera
  • Posted 05.30.18
  • NOVA

What kind of clues led to the discovery of dark matter and its place in the universe?

Running Time: 02:37


Dark Matter Clues

Published May 30, 2018

Onscreen: Why do we think dark matter exists?

Narrator: The first clue came from a Swiss astronomer named Fritz Zwicky. Just a few years after the discoveries that had suggested the Big Bang, Zwicky noticed that these newly discovered galaxies…were behaving oddly.

Alex Filippenko: Fritz Zwicky looked at clusters of galaxies and found that the individual galaxies within those clusters are moving so fast, that the clusters should fly apart.

Priya Natarajan: Moving around so rapidly, that it was impossible to understand why they didn't just wander away. Something clearly held them in these orbits.

Narrator: Zwicky could see nothing in his telescope to explain it, so he called the phenomenon…

“Dunkle mature" translated as “dark matter." And then the idea promptly faded away.

Zwicky’s observation might have ended up forgotten. And for nearly forty years, it was. Until an astronomer named Vera Rubin entered the field.

Flip Tanedo: Vera Rubin was one of these astronomers who was not appreciated until much later. She was a woman in astronomy at a time when the field was not particularly friendly to women.

Vera Rubin: Here’s what we get.

Narrator: She too noticed something bizarre was happening:

Rubin: The stars way out here are going very fast.

Narrator: The stars at the edge of the galaxies were moving so fast—that they should have been flung off into space.

André Fenton: Think about a spinning wheel, covered in water. If the wheel is moving slowly, the water clings to the wheel. But spin it fast enough, the water flies off.

The same thing should happen out in the universe. Stars swirling around in a galaxy. If they orbit too fast, they’ll get flung off out into space. Except that’s not what Vera Rubin sees.

Narrator: The galaxies are spinning fast—but the stars stay in their orbits.

What is holding them there? It has to be gravity.

Rubin: A gravitational pull from something that’s not bright. And we don’t know what that is.



Digital Producer
Michael Rivera
Produced and Directed by
Kirk Wolfinger & Owen Palmquist
© WGBH Educational Foundation 2018

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