Milky Way flipped in collision with dwarf galaxy 10bn years ago, astronomers say

Milky Way flipped in collision: Our Galaxy Underwent Dramatic Reorientation Following Ancient Collision A New Understanding of Galactic Evolution

Our Galaxy Underwent Dramatic Reorientation Following Ancient Collision

A New Understanding of Galactic Evolution

Wanderstayfinder.com – Scientists have uncovered compelling evidence that our Milky Way galaxy experienced a profound reorientation billions of years before Earth even existed. According to recent research, a direct encounter with a wandering companion galaxy caused our cosmic home to tilt significantly, fundamentally altering its structure and the way stars move within it.

The transformative event occurred approximately ten billion years in the past, when the Milky Way suffered a head-on impact from an incoming dwarf galaxy. This celestial intruder, designated the Gaia Sausage for astronomical classification purposes, collided with our galaxy with tremendous force. While the Milky Way ultimately absorbed the smaller galaxy’s stars and tore it apart, the violent interaction triggered a remarkable transformation.

Researchers suggest that the chaos generated during this encounter likely rotated the entire galactic disc by more than ninety degrees, establishing the orientation we observe in the present day. This dramatic shift represents one of the most significant structural changes in our galaxy’s long history.

Simulations Reveal the Mechanism

Scientists at Durham University employed advanced supercomputer simulations to demonstrate how galaxies similar to the Milky Way could experience such a dramatic reorientation during head-on collisions. Their computational models revealed that galaxies struck by companion bodies the size of the Gaia Sausage were highly susceptible to what they termed a “disc flip.”

This process did not happen instantaneously. The reorientation unfolded gradually over an extended period, fundamentally changing how the galaxy functioned as a rotating system of stars.

“It probably takes at least a few hundred million years,” explained Kirill Batrakov, who served as the lead researcher on this groundbreaking project.

The team’s investigation began when they examined an unusual characteristic of stars located in the Milky Way’s halo. This halo constitutes a sparse, roughly spherical cloud of stars that envelops the entire galaxy. The majority of these halo stars originated in smaller galaxies that drifted too close to the Milky Way and eventually merged with it over cosmic timescales.

Resolving a Stellar Rotation Mystery

Previous data collected by the European Space Agency’s Gaia mission had already established that stars within the Milky Way’s disc travel around the galactic center at approximately two hundred twenty kilometers per second, which translates to about one hundred thirty-seven miles per hour.

However, a persistent puzzle surrounded the stars in the halo. These distant stars rotate much more slowly, completing their orbits around the galactic center at roughly twenty-five kilometers per second. This significant discrepancy in rotational speeds had long puzzled astronomers seeking to understand galactic dynamics.

By analyzing computer simulations of evolving galaxies, the Durham research team discovered a clear explanation. Galaxies that experienced direct collisions with nearby dwarf galaxies similar to the Gaia Sausage subsequently underwent a disc flip, which resulted in the formation of halos containing slow-moving stars.

Historical Context and Future Events

The ancient collision was first identified in 2018 when an international collaboration of astronomers utilized additional observations from the Gaia mission to track stellar movements through the Milky Way. They discovered that certain stars followed distinctive sausage-shaped trajectories, which they traced back to a dwarf galaxy disintegrating as it plunged directly into the galactic core.

These extreme stellar orbits provided conclusive evidence for the massive collision, prompting astronomers to name the dwarf galaxy the Gaia Sausage. Today, scientists recognize this encounter as the galaxy’s most recent major merger and a pivotal moment in its evolution.

The collision fundamentally transformed the Milky Way, creating the central bulge and establishing the composition of the stellar halo. Despite being classified as a dwarf galaxy, the Gaia Sausage contained stars, gas, and dark matter totaling more than ten billion times the mass of our Sun.

Looking ahead, the next significant upheaval may not occur for several billion years, when the Large Magellanic Cloud, a nearby dwarf galaxy, eventually merges with the Milky Way. Meanwhile, another merger is currently in progress with the much smaller Sagittarius dwarf galaxy, though researchers expect this event to have considerably less dramatic consequences for our cosmic neighborhood.

“It’s not as massive as the Gaia Sausage was, so it is not going to influence the Milky Way as much, and the Milky Way itself is far more massive now than it was back then,” noted Batrakov regarding the ongoing Sagittarius merger.

These findings, presented at the Royal Astronomical Society’s National Astronomy Meeting in Birmingham, provide valuable insights into how galactic collisions shape the evolution of cosmic structures over billions of years.