Planck’s New Constraints on Dark Matter
6 January 2015
New Constraints on Dark Matter
New Revelations on Dark Matter
A number of astrophysical measurements on the scale of galaxies to the entirety of the visible Universe, point towards the existence of some sort of dark matter that appears to comprise roughly a quarter of the energy density of the Universe. The nature of the particles which make up this dark matter is essentially unknown, however, making the chase to understand and detect it one of the most compelling goals in astrophysics today.
Some models postulate dark matter which has significant annihilation. If this was the case, these annihilations would inject energy into the Universe. This, in turn, would change the spectrum and the anisotropies of the Cosmic Microwave Background (CMB). So, rather than directly detecting dark matter particles, Planck is searching for the changes we should see in the CMB anisotropies, if they exist.
In fact, such changes are not seen. Planck observations can be well-explained without ever invoking annihilating dark matter. Thus, Planck shows that strong dark matter-anti-dark matter annihilation did not occur in the early history of the Universe.
These new results are even more interesting when compared with measurements from other experiments. The Fermi satellite, the Pamela satellite, and the AMS-02 experiment on the International Space Station have all seen an excess of cosmic rays. One way to interpret these excesses might be as a consequence of dark matter annihilation.
Given the Planck observations, it now seems that slightly more pedestrian explanations such as radiation from a sea of undetected pulsars have to be considered. It should be noted, however, that the limits on decaying, as opposed to annihilating dark matter, are not strong.
Submitted by Ken Ganga
Laboratoire APC, France
Further reading:
Planck: New Revelations on Dark Matter and Relic Neutrinos
Latest Planck Results Improve our Knowledge on Dark Matter and Primordial Neutrinos
The Planck Mission Website