FROM an intergalactic pile-up comes the disturbing suggestion that mysterious dark matter is even more puzzling than we thought.
The massive galaxy cluster Abell 520, some 3 billion light years away, is thought to have formed from a collision between smaller clusters. When astronomers examined the wreckage, they found that Abell 520 has a massive dark core, empty of bright galaxies ().
Some of the core is made up of hot gas, but gravitational effects on light suggest that something else must be there too – and the astronomers think it’s dark matter.
Dark matter and galaxies are usually mixed…
