NEW HAVEN, Conn., Aug. 5 (UPI) -- Galaxies of today are bigger and denser than the most massive galaxies of the universe in its early days, U.S. astronomers said.
Recent observations of very distant massive galaxies -- located so far away that their light left them more than 10 billion years ago -- suggested that the galaxies were about five times smaller than similar galaxies of today even though they contain roughly the same amount of stars, researchers from Yale University and Swinburne University of Technology in Melbourne said in a news release issued by Yale.
However, they said their findings leave theorists with a puzzle: How did today's galaxies evolve?
Theoretical models of galaxy evolution can't explain how today's galaxies could have evolved from their more compact predecessors -- unless the masses of early galaxies were overestimated, researchers said.
Van Dokkum said he and his colleagues took an independent measurement of the mass of one of the smaller, outer galaxies, debunking a theory that an increase in the size of galaxies along with an increase in mass by galaxies merging would eventually result in today's larger galaxies.