That’s why the warped images of a distant galaxy — i.e., the arcs you mention — lensed by a foreground galaxy cluster appear blue. Liz Kruesi, Associate Editor ...

The galaxy’s eccentric characteristics were replicated very well, however, in simulations that incorporated an alternative leading dark matter candidate called ultralight axions.

A July 2012 study of the galaxy clusters Abell 222 and Abell 223 found they are connected by a dark matter filament, shown here. The blue shading and the yellow contours indicate the density of ...