“We’re winding back the clock to understand what it looked like one billion years ago, two billion years ago, and so on, back to the earliest times.” “Galactic archaeology is looking at the fossil record of our galaxy,” says Melissa Ness, an astronomer at Columbia University and the Center for Computational Astrophysics at the Simons Foundation. They’re learning how the galaxy grew, how its wide disk changed over the eons, and how it’s being influenced by other galaxies even now. And like archaeologists, astronomers are digging through the remains to help piece together the history of the Milky Way. Most of those galaxies are long gone (there’s one survivor, but it, too, is doomed). “But evidence now suggests that mergers of smaller galaxies play a very important role in this process.” “When I was growing up, the idea was that the galaxy formed by the monolithic collapse of a big cloud of gas,” says Simon Schuler, an assistant professor of physics at the University of Tampa. In short, those smaller galaxies helped mold the Milky Way into the magnificent spiral that spins through the universe today. Some of their gas and dust fell into our galaxy’s disk, giving birth to more stars. The stars and star clusters of the destroyed galaxies were forcibly annexed by the Milky Way, many of them taking up residence in its extended halo. It pulled in several smaller galaxies and ripped them to pieces. During its early years, the Milky Way was a bit of a hell-raiser. That hasn’t always been the case, though.
All that seems to be missing to complete this picture of contentment is a pair of slippers and a pipe. The disk of hot gas around the supermassive black hole at its core sometimes flares up, but not too brightly. A star occasionally explodes, but not too often. Our galactic home gives birth to a few stars a year, but not too many. The Milky Way Galaxy has settled into a comfortable, sedate life. Astronomers are deciphering the violent history of the Milky Way, one star at a time.
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