NS: Gamma rays may betray clumps of dark matter

[bystander]

Gamma rays may betray clumps of dark matter
New Scientist | Space | 04 July 2010

CLOUDS of dark matter the size of our solar system floating around the Milky Way may betray their presence by emitting gamma rays.

Dark matter is thought to make up most of the mass of the universe, but as it does not interact with light, it has never been directly observed. Now computer simulations by Tomoaki Ishiyama of the National Astronomical Observatory in Tokyo, Japan, and colleagues suggest a way to detect it.

Their model shows that the Milky Way should be littered with small clumps of dark matter, each about the size of our solar system. These would have been the first structures that formed in the universe. Earlier studies had suggested that the gravity of nearby stars would have ripped apart these primordial clumps, but the new simulations show that this would only happen in the crowded core of galaxies, leaving the clumps in the galactic suburbs intact.

At the centre of such clumps, dark matter particles would be colliding and annihilating, emitting gamma rays. NASA's Fermi Space Telescope is now looking for such light.

Gamma-ray Signal from Earth-mass Dark Matter Microhalos

• arXiv.org > astro-ph > arXiv:1006.3392 > 17 June 2010

[rstevenson]

Hmmmmm?

I thought we didn't know what dark matter is. Yet they say "... dark matter particles would be colliding and annihilating, emitting gamma rays." If they don't know what it is, how can they say it collides and annihilates, let alone what it might emit in doing so?

Rob