A trio of astronomers is studying dwarf galaxies darker than the night sky in hopes of explaining why researchers have been able to see less than 10 percent of the universe through telescopes.

Astronomers believe the mass is there because of its gravitational influence and the motion of star systems, and explain it with theories that include subatomic particles called neutrinos, and brown dwarfs larger than planets but too small to shine like stars.Christopher Impey of the University of Arizona favors a dim-galaxy theory.

Dwarf galaxies are dim because their stars are much farther apart than stars in the Milky Way, Impey says. In the newly charted Virgo galaxies, stars are 50 to 100 times farther apart than in our own, yet they contain a billion stars or more. While their total light output is substantial, the starlight is distributed so diffusely that no part of the galaxy is brighter than the sky.