Dark Matter Proved Real By Colliding Galaxy Clusters

It’s the 10th anniversary of dark matter’s most compelling proof.

“It may be that ultimately the search for dark matter will turn out to be the most expensive and largest null result experiment since the Michelson-Morley experiment, which failed to detect the ether.” -John Moffat

If you look at rotating galaxies or the motions of galaxies within clusters, there’s a mismatch between the matter we see and the gravitational effects we observe.

Traceable stars, neutral gas, and (even farther out) globular clusters all point to the existence of dark matter, which has mass but exists in a large, diffuse halo well beyond the normal matter’s location. Image credit: Wikimedia Commons user Stefania.deluca.

Even on the largest scales, the way galaxies clump and cluster together cannot be explained without some new physics.

Numerical simulation of the density of matter when the universe was 4.7 billion years old. Galaxy formation follows the gravitational wells produced by dark matter, where hydrogen gas coalesces, and the first stars ignite. This pattern in the Universe requires dark matter to match what’s observed. Image credit: V. Springel et al. 2005, Nature, 435, 629.

Observations show that it can’t be gas, dust, plasma or black holes; there’s truly something unaccounted for.