How heavy is dark matter?
Dark matter is a mysterious phenomenon. We do not know what it looks like or what it is made of. But physicists are convinced that it exists, because the effect of its gravitational pull can be observed in many examples in the cosmos. The visible universe - ourselves, the planets and stars - accounts for 25 percent of the total mass in the universe. The remaining 75 percent of its mass consists of dark matter. The fact that it interacts via gravity at least gives researchers a clue as to how heavy its particles might be. It was previously…