Around 10 million years ago, space experienced a galactic food fight: A little galaxy collided with our Milky Way, creating what astronomers have dubbed the “Gaia-Enceladus-sausage” (GES) merger. The cosmic sausage-meets-spaceship event stirred up the stars in our galaxy, flinging some of them into elongated, sausage-like 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 believe that the GES merger may have also played a role in shaping the Milky Way’s characteristic bar—a straight line of twinkling 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.
This artist’s illustration gives us a glimpse of the Milky Way, flaunting two major arms attached to the ends of a thick central bar. Credit: NASA/JPL-Caltech/R. Hurt (SSC/Caltech)
“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,” astronomers Alex Merrow and Robert Grand from Liverpool John Moores University share with PopSci.
Nearly two-thirds of all spiral galaxies have bars, and they play a crucial role in how stars, gas, and energy move throughout a galaxy due to their gravitational influence. Nonetheless, astronomers are still piecing together their origins. Even though we can’t go back in time to see the Milky Way’s beginnings, astronomers can dissect nearby stars of different ages in great detail for clues about the past. “Observational clues lie in starlight, much like fossils inform us about the Earth’s history,” astronomers Merrow and Grand explain. “In particular, the positions, motions, and chemical compositions of stars throughout the galaxy tell stories of our Cosmic past.”
New observations hinted that our galaxy’s bar might be quite old—perhaps 10 million years old, around the same time as the GES merger. To see if the merger could nudge stars in just the right way to form a bar, the researchers generated a computer simulation of a GES-like galaxy smashing into a Milky-Way-like galaxy, and then observed how the stars moved due to “gravity” over time. With this setup, the stars in the simulation formed into a bar fairly quickly, suggesting that this type of merger event could indeed create a galactic bar.
“It’s a cool result, especially since there’s a lot of evidence nowadays showing how the GES merger had a significant impact on a number of the Milky Way’s present-day properties,” Pratik Gandhi, a UC Davis astronomer unconnected to the new work, tells PopSci.
Our galaxy is also an important player in how we got here—living creatures on the tiny rock that is Earth. “In the Milky Way,
