Dark matter is thought to only interact through gravity, which is why it is so difficult to spot, but now evidence is growing for a type of dark matter that can also stick to itself “The dark matter density profile is consistent with what some of these self-interacting dark matter models predict,” says Collett. They found that the dark halo is almost certainly near the galaxy’s centre, as well as calculating the gravitational distribution of matter and dark matter, which matches self-interacting dark matter models.