Around 10 million years ago, a small galaxy collided with our Milky Way, creating a cosmic sausage. That so-called “Gaia-Enceladus-sausage” (GES) merger event stirred up the stars in our galaxy, flinging some of them into sausage-like elongated orbits around the galaxy’s central black hole and puffing up the Milky Way’s disk to its current thick, pancake-like shape.
Now, astronomers think that the GES merger might also be responsible for molding the Milky Way’s characteristic bar—a straight line of stars at the center of the galaxy’s spiral. Their findings were recently submitted to the journal Monthly Notices of the Royal Astronomical Society and are currently available on arXiv as a pre-print.
“Our paper shows, for the first time, that the Milky Way’s bar could have been created as a direct result of the Galaxy’s biggest merger [the Gaia-Enceladus-Sausage merger], whose remnants we can see in the motions of nearby stars,” authors Alex Merrow and Robert Grand, astronomers at Liverpool John Moores University tell PopSci.
Nearly two-thirds of all spiral galaxies have bars, and they’re a crucial piece of the puzzle of how stars, gas, and energy move throughout a galaxy because of their gravitational influence. However, astronomers don’t fully understand how they came to be. Although we can’t travel back in time to see the Milky Way’s origins, astronomers can study nearby stars of different ages in great detail, providing clues about the past. “Observational clues lie in starlight, much like fossils inform us about the Earth’s history,” Merrow and Grand explain. “In particular, the positions, motions, and chemical compositions of stars throughout the galaxy tell stories of our Cosmic past.”
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