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 鈥� and the astronomers think it鈥檚 dark matter.
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Dark matter and galaxies are usually mixed up together, though, so why are they separated here? One possibility is that close encounters between galaxies threw them out of the core to the fringes. The team cannot get that to happen in computer simulations, however.
Another possibility is that dark matter may have been stripped out of the original clusters as they collided. But dark matter is supposed to be very slippery, barely interacting with other matter or even with itself. 鈥淲e expect clouds of dark matter to flow right through each other,鈥� says team member Arif Babul, at the University of Victoria in British Columbia, Canada.
Next the team hopes to train the Hubble Space Telescope onto Abell 520 in order to get a closer look.
