A Hubble image of galaxy cluster MACS J0717, which contains a huge amount of information about the cluster itself thanks to the light from background galaxies. Image credit: ESA/Hubble, NASA and H. Ebeling.

Galaxy clusters prove dark matter’s existence

You don’t have to detect a particle to know that dark matter is real.

Ethan Siegel
Jan 10, 2017 · 3 min read

“You may hate gravity, but gravity doesn’t care.” –Clayton Christensen

In the 1970s, Vera Rubin’s observations showed galactic rotation was too quick at the outskirts for normal matter alone to explain.