Wobbling galaxies: New evidence for dark matter

[wolram]

https://www.sciencedaily.com/releases/2017/10/171026103110.htm

Astronomers have discovered that the brightest galaxies within galaxy clusters 'wobble' relative to the cluster's center of mass. This unexpected result is inconsistent with predictions made by the current standard model of dark matter. With further analysis it may provide insights into the nature of dark matter, perhaps even indicating that new physics is at work.

Is this a matter of incorrect observation or is it real?

 

[ohwilleke]

https://www.sciencedaily.com/releases/2017/10/171026103110.htm

Astronomers have discovered that the brightest galaxies within galaxy clusters 'wobble' relative to the cluster's center of mass. This unexpected result is inconsistent with predictions made by the current standard model of dark matter. With further analysis it may provide insights into the nature of dark matter, perhaps even indicating that new physics is at work.

Is this a matter of incorrect observation or is it real?

The press release at Science Daily notes near the end that:

If this "wobbling" is not an unknown astrophysical phenomenon and in fact the result of the behaviour of dark matter, then it is inconsistent with the standard model of dark matter and can only be explained if dark matter particles can interact with each other -- a strong contradiction to the current understanding of dark matter.

The wobbling observation is very likely to be real as it is a close analogy of the long known "cusp-core" problem with Cold Dark Matter. See, e.g., https://arxiv.org/pdf/1305.7452v2.pdf

But, the need for self-interacting dark matter (SIDM) to solve the problem is huge, because all astrophysically relevant parameters for SIDM have been ruled out by other data. See:

Torsten Bringmann, et al., "Strong constraints on self-interacting dark matter with light mediators" (December 2, 2016). Abstract:

Coupling dark matter to light new particles is an attractive way to combine thermal production with strong velocity-dependent self-interactions. Here we point out that in such models the dark matter annihilation rate is generically enhanced by the Sommerfeld effect, and we derive the resulting constraints from the Cosmic Microwave Background and other indirect detection probes. For the frequently studied case of s-wave annihilation these constraints exclude the entire parameter space where the self-interactions are large enough to address the small-scale problems of structure formation.

The conclusion of the paper notes that:

Models of DM with velocity-dependent self-interactions have recently received a great deal of attention for their potential to produce a number of interesting effects on astrophysical scales. We have shown in this Letter that these models face very strong constraints from the CMB and DM indirect detection. In the most natural realization of this scenario with a light vector mediator with kinetic mixing, these constraints rule out the entire parameter space where the self-scattering cross section can be relevant for astrophysical systems. These bounds remain highly relevant for a number of generalizations of the scenario, such as a different dark sector temperature and different mediator branching ratios. Clearly, future efforts to develop particle physics models for SIDM need to address these issues in order to arrive at models that provide a picture consistent with all observations in cosmology, astrophysics and particle physics.