Dark matter content wimpy, simulation suggests

17 Jun 2002

When a team at the University of California, Santa Cruz, used a supercomputer model of colliding galaxies as a novel way to probe how much dark matter is out there, they unveiled a puzzle. The model's collisions created dramatic "tidal tails" of stars only when the mass of each galaxy's dark-matter halo was fairly low. But popular theories predict that galaxies should have huge cocoons of dark matter. Several well-known galaxy pairs have hurled tremendous tails of stars into space. This implies--according to the computer model--that their dark-matter halos are wimpy, not massive.

"It's not controversial that dark matter exists around galaxies," says John Dubinski, postdoctoral researcher in astronomy and astrophysics at UC Santa Cruz. "What's controversial is how much there is. We found that our simulations can't produce these beautiful long tidal tails if the galaxies have high-mass halos of dark matter." The findings were reported in the 10 May issue of the Astrophysical Journal.