The Milky Way is one galaxy — but it used to be thousands, new simulations reveal

Long before it became the luminous spiral galaxy we call home, the Milky Way was a sprawling, chaotic swarm of thousands of small galaxies, new research shows.

The findings suggest that in the first 2 billion years after the Big Bang , the region of the universe that would become our galaxy was littered with thousands of smaller galaxies of many sizes and shapes.

Over time, these galaxies collided and merged into the single galaxy in which we reside today.

"Looking at these results, it's very clear that the physics happening right after the Big Bang has direct impact on what we see today in the local universe," study co-author Harley Katz , an assistant professor of astronomy and astrophysics at the University of Chicago, said in a statement .

To understand more about the early universe, astronomers build sophisticated computer models that encode the laws of nature to see how the cosmos may have evolved.

The new work, which is the result of three years of supercomputer simulations, is the most detailed tracing yet of how a galaxy like ours came to be.

It also arrives just as astronomers need a stronger yardstick for what they're seeing in the early universe.

Megatron, the cosmic transformer The James Webb Space Telescope ( JWST ) can peer farther into the early universe than any previous telescope, and its discoveries have often defied computer models.

For instance, JWST found surprisingly bright early galaxies and a mysterious new class of compact galaxies dubbed " Little Red Dots ." These anomalies demonstrate that current computer models need an update to handle the complex physics of the early universe, the researchers said.

To bridge that gap, the scientists built a new suite of supercomputer simulations they call Megatron.

By tracing ancient gas, starlight and chemistry from 180 million years to 2 billion years after the Big Bang, Megatron predicts the distinct light signatures of its virtual galaxies, according to the statement.

Because JWST collects the same type of spectral data across a similar span of cosmic time, scientists can directly cross-reference the simulation against real observations to pinpoint what the old models are missing, the team said.

The simulation also tracks how the universe's first stars formed, died and forged the essential elements that make life as we know it possible.

By comparing the simulation with JWST observations of early galaxies and with the chemical traces left in ancient stars, scientists can better understand how those first stars enriched their surroundings, the researchers said.