Celestial Divide: Finding two families of galaxies

By analyzing data from a huge sky survey, researchers have found that galaxies divide into two distinct families. Those galaxies whose stars collectively weigh more than 30 billion times the mass of the sun are old and staid and appear to have finished formation of most of their stars billions of years ago. In contrast, galaxies with stellar populations weighing less than 30 billion suns are young and still forming stars.