July 23 - Happy Birthday, Vera Rubin

Posted on July 23, 2020

Today's famous birthday was an American astronomer who was born in Philadelphia (Pennsylvania) in 1928.

Vera Rubin studied galaxy rotation rates - and she discovered a puzzle: the predicted angular motion of each galaxy didn't match the motion she observed.

If you think about how tiny galaxies appear in our skies...

This is the largest of the nearest galaxies -
and it's just a tiny smudge to the naked eye,
even under the darkest-sky conditions...

...then you may be wondering how Rubin measured any galaxy's rotation?

It's not like we're treated to sights like this!
Rubin and other astronomers take advantage of the Doppler effect. Light that is coming towards us is bluer than expected, and light that is going away from us is redder than expected. So an astronomer looks for galaxies with bluer light on one side and redder light on the other - and then she can compute the rotational speed.

Well, Rubin measured many, many galaxies' rotation - and she discovered that galaxies rotated quickly enough that they should fly apart! Since they didn't fly apart, she knew that there must be more mass - about five times more! - than we could see.

A Swiss astronomer named Fritz Zwicky had already proposed the existence of dark matter - matter we can't see, but that we can tell exists because of its gravitational pull. Rubin's work was some of the first evidence for his idea - but at first many scientists were very skeptical!

However, more and more scientists were able to confirm Rubin's data, find more evidence to back the theory that dark matter exists, and that there is WAY more of it than there is of matter we can see! 

Astrophysicists now believe that the normal matter
we see all around us and across our night skies is
only a very small part of what the universe if made of!

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