These two Hubble images show gravitationally lensed galaxies and their halos (pink), as well as the galaxy clusters (yellow) responsible for the lensing. Gravitational lensing often results in more than one image of a single galaxy (right), or sometimes smears that light out into a ring (left). (Credit: ESO/NASA/ESA/A. Claeyssens)

Galaxies are not just the glowing stars and gas you see through a telescope. They are swaddled in a huge ball, or “halo,” of hydrogen that stretches vast distances