A look back in time reveals Milky Way’s evolution

A compilation of over 2,000 galaxies gives insights into the history of the Milky Way. By looking at progressively more distant galaxies, astronomers have gazed back in time to create a flip-book documenting how our galaxy has changed over most of the universe’s 13.8-billion-year history.

By the time the universe was about 3 billion years old, galaxies like the Milky Way were already tens of thousands of light-years across and blazing with the blue light of young stars, Casey Papovich, an astrophysicist at Texas A&M University in College Station, and colleagues report in the April 10 Astrophysical Journal. The stellar factories churned out nearly 30 new stars a year at their peak roughly 9 billion years ago — more than 10 times as many as the Milky Way produces now. At the same time, interstellar dust shrouded the stars as the galaxy filled with the soot cast off from dying stars. By the time the sun came on the scene 4.6 billion years ago, star formation had already abated to a mere trickle.

The researchers also pieced together the history of the more massive Andromeda galaxy. They found that galaxies like Andromeda follow in the same footsteps as the Milky Way but reach each milestone earlier in their life span.