Last Updated on July 21, 2026 by Staff
The Milky Way may have gone through a big change billions of years ago. This is what some astronomers from Durham University said when they talked about their research at the Royal Astronomical Society’s National Astronomy Meeting in Birmingham. They think that the Milky Way’s disk may have flipped by more than 90 degrees as it was forming. This is an idea that could help us understand why the Milky Way’s stellar halo rotates so slowly. It could also tell us more about the Milky Way’s past.
The Milky Way is a galaxy with a lot of stars. Astronomers used computers to see how galaxies like the Milky Way might have formed over billions of years. What they found out is that galaxies with rotating stellar halos often had a big collision with another galaxy. After that the galaxy’s disk would flip over. This is what might have happened to the Milky Way.
The Halo
Most of the stars in the Milky Way are in the bright spiral disk. This is where our solar system is. There is a bigger area around the disk called the stellar halo. The stellar halo has stars that were formed in galaxies. These galaxies were pulled into the Milky Way. Became part of it. The European Space Agency’s Gaia mission found out that the Milky Ways disk rotates fast. Its stellar halo rotates very slowly. Astronomers did not know why this was the case until now.
Simulating the Past
Astronomers used computers to see how the Milky Way might have formed. They looked at 25 galaxies that’re similar to the Milky Way. What they found out is that galaxies with stellar halos had two things in common. They had a collision with another galaxy and their disk flipped over. This means that the stars in the galaxy started orbiting in a direction.
The Gaia Sausage Collision
The Milky Way had a collision with a dwarf galaxy called the Gaia Sausage about 10 to 11 billion years ago. This collision left behind a lot of stars that are still moving in orbits. The astronomer in charge of the research Kirill Batrakov thinks that this collision might have caused the Milky Way’s disk to flip. If that is true then our own Sun was moving in a different direction than it is now.
Why It Matters
The Milky Way is a galaxy because we can study it easily. If the Milky Ways disk really did flip then we have to rewrite the history of our galaxy. This research can also help us learn more about matter which is a mysterious substance that makes up most of the galaxy’s mass. What the astronomers found out is that the stellar halo and the dark matter halo are connected. They both formed when smaller galaxies merged into the Milky Way.
Looking Ahead
The research is based on computer simulations. It matches what we see in the real world. Future missions will help us find out if the Milky Way really did flip. If it did then we will have to change our understanding of the Milky Way’s history. The research shows us that by using computers and space observations we can learn about events that happened billions of years ago. As we keep studying the Milky Way we will find out more about its past. How it was formed. The idea that the Milky Way might have rotated in a direction is a reminder that there is still a lot to learn about the universe.