Just a little something whilst a dark matter pioneer moves onto a better place.
This commentator writes:
My understanding is that dark matter was "discovered" when trying to find out why stars in the outer edge of a galaxy rotates with the same speed as the inner. A ten-fold increase in number of galaxies doesn't seem to affect this.
When reading the history - this simple explanation doesn't quite come across. Perhaps the statement above is oversimplified. For example:
- mass in the galactic plane must be greater than what was observed (doesn't quite talk about comparative rotational velocity)
- estimated its mass based on the motions of galaxies near its edge (doesn't quite talk about comparative rotational velocity)
- some unseen matter provided the mass and associated gravitation attraction to hold the cluster together (doesn't quite talk about comparative rotational velocity)
- measurements of galaxy rotation curves (what is a galaxy rotational curve? Shouldn't it be a straight line if they're rotating at the same angular velocity?)
- gravitational lensing of background objects by galaxy clusters (not talking about comparative rotational velocity?)
My question is: Is it true dark matter was discovered whilst looking at the rotational speed of galaxies?