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The concordance model strikes back

23 Oct 2016, 07:03 UTC
The concordance model strikes back
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Two weeks ago, I summarized a recent paper by McGaugh et al who reported a correlation in galactic structures. The researchers studied a data-set with the rotation curves of 153 galaxies and showed that the gravitational acceleration inferred from the rotational velocity (including dark matter), gobs, is strongly correlated to the gravitational acceleration from the normal matter (stars and gas), gbar.Figure from arXiv:1609.05917 [astro-ph.GA] This isn’t actually new data or a new correlation, but a new way to look at correlations in previously available data. The authors of the paper were very careful not to jump to conclusions from their results, but merely stated that this correlation requires some explanation. That galactic rotation curves have surprising regularities, however, has been evidence in favor of modified gravity for two decades, so the implication was clear: Here is something that the concordance model might have trouble explaining. As I remarked in my previous blogpost, while the correlation does seem to be strong, it would be good to see the results of a simulation with the concordance model that describes dark matter, as usual, as a pressureless, cold fluid. In this case too one would expect there to be some relation. Normal matter ...

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