Astronomers have found new evidence that the number of galaxies in the universe is not 10 billion, as previously believed, but 50 billion  This discovery will have an important effect on theories about how galaxies are formed
But even though astronomers now believe 40 billion more galaxies exist, many astronomers' estimates of the universe' s total mass remain virtually unchanged
The number of galaxies that astronomers believe exist tends to grow as the instruments used to detect galaxies become more sophisticated.