New research suggests that the most recent major collision in our galaxy occurred billions of years later than previously thought.
Using data from the Gaia space probe, researchers found that the Milky WayThe last major galactic collision occurred less than three billion years ago, not eight to eleven billion years ago as originally thought.
Heidi Jo Newberg, Ph.D., professor of astronomy at Rensselaer Polytechnic Institute, Tom Donlon, Ph.D., visiting scientist at Rensselaer and postdoctoral fellow at the University of Alabama, and their team recently published research that reveals a shocking discovery about the history of our universe: The last major collision in the Milky Way occurred billions of years later than previously thought.
The discovery was made possible by the European Space AgencyAstronomy Research’s Gaia spacecraft maps over a billion stars in the Milky Way and beyond, tracking their motion, luminosity, temperature and composition. Newberg, a renowned astrophysicist and Milky Way expert, and Donlon focused on the so-called “wrinkles” in our galaxy that form when other galaxies collide with the Milky Way.
“We get more wrinkled as we age, but our work shows that the opposite is true for the Milky Way. It’s a sort of cosmic Benjamin Button that gets less wrinkled over time,” said Donlon, lead author of the new Gaia study, which also served as his doctoral thesis at Rensselaer. “By studying how these wrinkles resolve over time, we can trace back when the Milky Way experienced its last major collapse – and it turns out that it happened billions of years later than we thought.”
A revised galactic timeline
By comparing their observations of the folds with cosmological simulations, the team was able to determine that our last significant collision with another galaxy did not actually occur eight to eleven billion years ago, as previously thought.
“For the folds in the stars to be as clear as they appear in the Gaia data, they must have joined us at least three billion years ago – at least five billion years later than previously thought,” said Newberg, Donlon’s doctoral supervisor at Rensselaer. “Every time the stars swing back and forth through the center of the Milky Way, new folds in the stars form. If they had joined us eight billion years ago, there would be so many folds right next to each other that we would no longer recognize them as separate structures.”
Impact of the new findings
The collision is thought to have produced a large number of stars with unusual orbits. Scientists had previously dated the event to be between eight and 11 billion years old, dubbed the Gaia-Sausage-Enceladus (GSE) collision. However, Newberg and Donlon’s results suggest that the stars may have been formed from the Virgo Radial Merger, which crashed through the center of the Milky Way less than three billion years ago.
“Gaia is a highly productive mission that is changing the way we see the cosmos,” says Dr. Timo Prusti, Gaia Project Scientist at the European Space Agency. “Results like these are only possible through the incredible teamwork and collaboration of a large number of scientists and engineers across Europe and beyond.”
“With this study, Dr. Newberg and Dr. Donlon have made an amazing discovery about the history of the Milky Way,” said Curt Breneman, Ph.D., dean of the School of Science. “Gaia data offer unprecedented opportunities to better understand our universe, and I am thrilled that Rensselaer researchers were able to harness the power of this incredibly detailed new data.”
Reference: “The wreckage of the ‘last great merger’ is dynamically young” by Thomas Donlon, Heidi Jo Newberg, Robyn Sanderson, Emily Bregou, Danny Horta, Arpit Arora and Nondh Panithanpaisal, May 16, 2024, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stae1264
Newberg and Donlon were supported in their research by Dr. Robyn Sanderson of the University of Pennsylvania and Flatiron Institute; Emily Bregou, Ph.D., Arpit Arora, Ph.D., and Nondh Panithanpaisal, Ph.D. of the University of Pennsylvania; and Danny Horta, Ph.D., of the Flatiron Institute and the Astrophysics Research Institute.
