The matter that’s not not not there
Jon Butterworth: Our local dark matter stages a comeback
Astronomers study the motion of stars in galaxies, as they twist and rotate under each other’s gravitational attraction. The motion throws up a long-standing puzzle in astrophysics: The way the stars move indicates the presence of a certain amount of matter in the galaxies. But when you count up the matter in the visible stars, there isn’t enough. This matter that’s “not there” in the visible galaxy is called “dark matter”. No one knows what it is. It could for example by supersymmetric fundamental particles, which we might see in high energy particle colliders like the LHC, although none has put in an appearance so far. Several highly sensitive experiments huddled deep underground, where backgrounds are low, are hunting for hints of low-energy collisions between the atoms of the detectors and the dark matter particles the Earth is presumably passing through on its path through space. Despite some hints, no compelling discovery has been made yet. This is one of the frontiers of knowledge. Either dark matter is about 80% of the matter in the universe and we don’t know what it is, or our theory of gravity is wrong. One way or another, we want to know. (via The matter that’s not not not there | Jon Butterworth | Life & Physics | Science | guardian.co.uk)





