What is dark matter?

Dr Steve Curran, from the School of Chemical and Physical Sciences, discusses Dark matter.


Dr Steve Curran, from the School of Chemical and Physical Sciences, answers:

No one knows what dark matter is but it’s evident through its gravitational effects. We see it in clusters of galaxies and within galaxies themselves. A galaxy is a disc of stars and gas—it’s very tenuous, with huge distances between the stars. Galaxies collide all the time, but they move through each other, there’s no real collision. A galaxy should behave like a fluid—like water down a plughole—but they don’t, they behave like solid wheels, the outside moving the same speed as the inside at about 200km per second. At that speed they should fly apart, but they don’t—something dark is holding them together but we don’t know what it is.