Science / Medicine : Dwarf Galaxies Puzzle Astronomers

Conventional ideas of galaxy formation are challenged by new discoveries reported last week in the journal Nature by astronomer Lennox L. Cowie and his colleagues at the University of Hawaii at Manoa. They studied faint blue galaxies, which contain many stars in the process of forming, and found that half of them are quite small, containing only about one-tenth to one-hundredth the mass of the Earth’s Milky Way galaxy. Light from the galaxies they studied originated 3 billion to 5 billion years ago.

Currently, the number of dwarf galaxies in the universe is only about one-tenth as high as the number that was present 3 billion years ago. Astronomers must therefore figure out where all the small galaxies went in the relatively short time that has elapsed.

Cowie said there are only two possibilities: Either the dwarf galaxies merged to form larger ones that then evolved into present-day galaxies, or they were destroyed, died out or became too faint to see. Either conclusion “will require a substantial revision of current ideas about galaxy formation,” wrote physicist Cedric Lacy of Oxford University in the same issue of Nature. Current theories do not accommodate the rapid disappearance of so many dwarf galaxies.