Dark matter is thought to be an invisible substance that makes up almost a quarter of the mass in the universe. The concept was first proposed in 1933 to explain why the outer galaxies in galaxy clusters orbit faster than they should, based on the galaxies' visible mass.
At the observed speeds, the outer galaxies should be flung out into space, since the clusters don't appear to have enough mass to keep the galaxies at their edges gravitationally bound.
So physicists proposed that the galaxies are surrounded by halos of invisible matter. This dark matter provides the extra mass, which in turn creates gravitational fields strong enough to hold the clusters together.
In the new study, physicist Dragan Hajdukovic at the European Organization for Nuclear Research (CERN) in Switzerland proposes an alternative explanation, based on something he calls the "gravitational polarization of the quantum vacuum."
The quantum vacuum is the name physicists give to what we see as empty space.