Thursday, May 10, 2012

CDM particle properties

what statements about the properties of the dark matter particles can we make by observing cosmic structures?


  1. Observations of cosmic structure tell you about the temperature (re: velocity) of dark matter particles. We know that dark matter is not hot, as the large scale structure gets washed out when particles move at relativistic speed, and so cold (non-relativistic particles) is favoured, although now the question of warm dark matter (mildly relativistic) is being reconsidered as it would agree with the large scale structure, but wash out the small scale structure which appears to be missing within the halos of large galaxies like the Milky Way

  2. yes, Cusp is quite right about this! I'd like to add that we know about the collosionlessness of CDM particles, i.e. that their cross-section for doing elastic collisions is very small, otherwise the core structure of haloes would be different, and we know that they don't show appreciable decay into other particles (this would either change the Hubble function or put energy into the ICM, both affecting structures). we can't measure the CDM particle mass but only infer it's mass density.