Researchers have used advanced computer simulations to show that the space between galaxies is teeming with dark matter.
Everything that we can see around us in the Universe only makes up around 4.5 per cent of the total mass of the Universe. The remaining “missing mass” is made up of dark matter and dark energy, and the origin of both of these is still a mystery.
While dark matter cannot be directly detected, its presence can be inferred from an effect known as gravitational lensing. Light from a distant object, such as a quasar, is bent around a foreground galaxy so that the light from the quasar becomes distorted. The way in which the light is bent depends on the mass of the “lens” galaxy.
The image on the left shows a simulation of how light from distant sources should appear if there is no intervening “lens,” while the image on the right shows how light can be distorted when there is a galaxy between us and the distant light sources.
However the mass of galaxies is usually much greater than what is expected from looking at the amount of matter that is visible. It has been known for some time that large dark matter halos exist around galaxies, which stretch up to 100 million light years from the centre of the galaxies.
New computer simulations now show that the dark matter does not end at 100 million light years, but instead knows no boundaries as it extends into intergalactic space.
Taking the extra dark matter between galaxies into account explains a discrepancy between two different methods of calculating the masses of galaxies.