Giant, low-surface-brightness galaxies

Forty years ago, astronomers using sensitive new imaging techniques discovered a class of large, faint galaxies they named low-surface-brightness galaxies. Giant low-surface-brightness galaxies (gLSBGs) are a subset whose masses are comparable to the Milky Way's but whose radii are ten times bigger, as much as four hundred thousand light-years. These gLSBGs raise a problem for astronomers: despite being massive, the galaxy disks are (kinematically speaking) relatively inactive. The usual formati...