Washington: Astronomers have discovered that galaxies in the distant universe behave in one of two ways – they are either awake or asleep, actively forming stars or are not forming any new stars at all.
Scientists have known for several years that galaxies in the nearby universe seem to fall into one of these two states. But a new survey of the distant universe shows that even very young galaxies as far away as 12 billion light-years are either awake or asleep as well, meaning galaxies have behaved this way for more than 85 percent of the history of the universe.
“The fact that we see such young galaxies in the distant universe that have already shut off is remarkable,” said Kate Whitaker, a Yale
University graduate student and lead author of the paper.
The researchers also found that there are many more active galaxies than passive ones, which agrees with the current thinking that galaxies start out actively forming stars before eventually shutting down.
“We don’t see many galaxies in the in-between state,” said Pieter van Dokkum, a Yale astronomer and another author of the paper. “This discovery shows how quickly galaxies go from one state to the other, from actively forming stars to shutting off.”
Whether the sleeping galaxies have completely shut down remains an open question, Whitaker said.
The study was recently published in the online edition of the Astrophysical Journal.