The Milky Way may have gone through a violent cosmic collision billions of years ago that dramatically changed the structure of our galaxy, according to a new study led by researchers at Institute of Cosmos Sciences of the University of Barcelona and Institute of Space Studies of Catalonia.
The research suggests that a major crash with another galaxy around 11 billion years ago may have partially destroyed the Milky Way’s early stellar disk before the galaxy rebuilt itself into the spiral shape we see today.
The findings were published in the Monthly Notices of the Royal Astronomical Society.
The Milky Way’s disk is the large, flat, rotating region where most of the galaxy’s stars are found, including our sun.
It contains the familiar spiral arms that stretch across the night sky. Astronomers have long tried to understand exactly when this rotating disk first formed.
One way scientists investigate this question is by studying how stars move.
At some point in the galaxy’s early history, stars began orbiting together in an organized spinning pattern. Researchers call this moment the galaxy’s “spin-up” time.
For many years, scientists believed this spin-up might mark the birth of the Milky Way’s disk. But the new study suggests the story is much more complicated.
Using advanced computer simulations known as the Auriga simulations, researchers studied how galaxies similar to the Milky Way evolve over billions of years. The simulations showed that rotating disks can form surprisingly early in a galaxy’s life, but major galactic collisions can later disrupt or even destroy them.
This means the Milky Way’s current rotating disk may actually represent a rebuilt version of an older structure that was damaged in an ancient collision.
Scientists believe the most likely culprit was a smaller galaxy involved in an event known as the Gaia-Sausage-Enceladus merger. Evidence for this merger was discovered in 2018 using data from the Gaia mission. Researchers identified a large population of stars moving in unusual ways, suggesting they originally came from another galaxy that collided with the Milky Way.
The new study now suggests this massive collision likely happened around 11 billion years ago, earlier than many previous estimates.
Importantly, this timing matches another major event in the Milky Way’s history: a sudden burst of star formation. The researchers found evidence that large numbers of star clusters formed at the same time as the collision.
According to the scientists, this makes sense because galactic collisions compress huge clouds of gas, triggering rapid star formation, almost like a cosmic fireworks display.
Researcher Chervin F. P. Laporte explained that this is the first time scientists have directly linked the Gaia-Sausage-Enceladus merger with a burst of globular cluster formation in the Milky Way.
Because humans cannot observe the Milky Way’s past directly, astronomers rely on simulations and observations of distant galaxies that formed long ago. Powerful modern instruments such as the James Webb Space Telescope and Atacama Large Millimeter/submillimeter Array are helping scientists study how galaxies grow and collide across the universe.
Source: KSR.
