The Andromeda galaxy is one of our Milky Way’s closest neighbors. Its proximity gives astronomers an opportunity to investigate it in great detail. NASA’s Hubble Space Telescope has conducted two gigantic surveys that combined to image about two-thirds of the galaxy’s disk. Using that data, a team of researchers has measured 200 million individual stars to tease out the history of star formation in Andromeda. They found that star formation has decreased dramatically over the past 500 million years. And they asked: Is Andromeda in the late stages of a longer decline, or is it “running out of gas”?

“This project is the combination of multiple decades worth of experience to really get a holistic picture of the Andromeda galaxy,” said lead author Tobin Wainer of the University of Washington.