Scientists initially presumed the Milky Way’s last major collision was the Gaia-Sausage-Enceladus merger, dated between eight and 11 billion years ago. However, a new study reveals that the Milky Way Galaxy’s last major collision occurred billions of years later than previously thought.
According to the study, the Milky Way’s last significant collision with another galaxy occurred more than three billion years ago. The data for this study were gathered from the European Space Agency’s Gaia spacecraft.
Using these observations, scientists focused on the galaxy’s wrinkles, which are the features that occurred after the galactic collision.
Dr. Tom Donlon, a postdoctoral researcher at The University of Alabama in Huntsville (UAH), a part of the University of Alabama System, said, “We get wrinklier as we age, but our work reveals that the opposite is true for the Milky Way.”
“It’s a cosmic Benjamin Button, getting less wrinkly over time. Looking at how these wrinkles dissipate, we can trace when the Milky Way experienced its last big crash — and it turns out this happened billions of years later than we thought.”
Scientists made the discovery by comparing the wrinkle observations with cosmological simulations. For their creases to be as noticeable as they are in Gaia data, stars had to have joined us at least three billion years ago or at least five billion years later than previously believed.
Professor of physics and astronomy Dr. Heidi Newberg said, “New wrinkles of stars form each time the stars swing back and forth through the center of the Milky Way. If they’d joined us eight billion years ago, there would be so many wrinkles right next to each other that we would no longer see them as separate features.”
The most recent significant encounter was the Virgo Radial Merger, which crashed through the center of the Milky Way less than three billion years ago.
Dr. Timo Prusti, ESA’s project scientist for Gaia, said, “Gaia is a hugely productive mission transforming our view of the cosmos. Results like this are made possible due to incredible teamwork and collaboration between many scientists and engineers across Europe and beyond.”
Journal Reference:
- Thomas Donlon, Heidi Jo Newberg, Robyn Sanderson, Emily Bregou et al. The debris of the ‘last major merger’ is dynamically young. Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stae1264