What is the Bullet Cluster?
3 min readMar 11, 2023
In the 1970s, the astronomer Vera Rubin was observing how the rotation of spiral galaxies changed as she looked along the radius, from the centre to the extreme edge.
With a bit of basic Newtonian mechanics — which is sufficient for studying galactic dynamics like this, without venturing into general relativity — the rotation speed is predicted to decrease as you move further from the centre. Yet, instead, Rubin…
