The four colliding galaxies with their large masses are clearly marked in the blue lines that trace dark matter. But the leftmost galaxy’s dark matter lags behind its stars, an unusual feature. The ghostly swirls to the right are lensed images of even more distant galaxies whose light is bent by the foreground cluster.
ESO/R. Massey
Awesome and important space stories abounded in 2015, and just like every year, it’s a struggle to pick just 10 for our list. Here are other important discoveries, developments, or achievements that also deserve honorable mentions.
