About a century ago, astronomers started noticing that some objects in the universe behaved in strange ways. Galaxies, for example, were observed spinning far too fast for their mass. At the rates they were spinning, stars and gas towards the edges should have been flying off into space – but they stayed. In other observations light travelling from distant stars would bend as though tugged by the gravity of massive objects, though no massive objects could be seen. All of this evidence suggested the same conclusion: there must be additional matter in the universe. Since it interacts only with gravity, this additional mass was named dark matter.
Missing mass: the hunt for dark matter
Astronomers and astrophysicists have calculated that most of the matter in the universe is actually dark matter – about 95% of all the matter in the universe is dark. Dark matter doesn’t interact with the electromagnetic spectrum (light, microwaves, radio waves, etc.) at all, and we only know it exists because of how its mass interacts with gravity. This makes detecting it very challenging since none of the tools scientists usually use to study astronomical objects work. Physicists design large detector experiments, hoping to detect the physical interaction of a dark matter particle hitting the target material.
To learn more about dark matter, check out the dark matter experiments at SNOLAB.