The problem with dark matter

The evidence that dark matter is real is all but irrefutable.

The distribution of dark matter, galaxies, and hot gas in the core of the merging galaxy cluster Abell 520, was formed from a violent collision of massive galaxy clusters 2.4 billion light years from Earth. Credit: NASA / ESA / CFHT / CXO / M.J. Jee (University of California, Davis) / A. Mahdavi (San Francisco State University)