Scientists have long known that a galaxy can basically be said to exist in one of two states, asleep or awake, actively forming new stars or lying dormant. But a new study published in a June 20 issue of the Astrophysics Journal adds to this knowledge the old adage that the more things change the more they stay the same.
Headed by Yale grad student Kate Whitaker, the study observed galaxies up to 12 billion light-years away. Light spectrum analysis divided them into two categories: blue or red, awake or asleep. Since the galaxies are so far away, what Whitaker and her colleagues were really observing was the distant past — by the time light from 12 billion light-years away reaches us, 12 billion years have passed.
The conclusion? Galaxies have been behaving this way for over 85 percent of the universe’s history, and the sleepy, dormant galaxies aren’t just the old ones.
“The fact that we see such young galaxies in the distant universe that have already shut off is remarkable,” Whitaker says.
“Next, we hope to determine whether galaxies go back and forth between waking and sleeping or whether they never wake up again,” says Pieter van Dokkum, a Yale astronomer and co-author of the paper.