These galaxies may constitute an answer to the long-standing puzzle of the missing

baryonic mass in the universe. Baryons—subatomic particles亚原子粒子 that are generally protons or neutrons—are the source of stellar, and therefore galactic, luminosity, and so their numbers can be estimated based on how luminous galaxies are. However, the amount of helium in the universe, as measured by spectroscopy光谱学, suggests that there are far more baryons in the universe than estimates based on galactic luminosity indicate. Astronomers have long speculated that the missing baryonic mass might eventually