Harley Katz remembers the moment he first saw the simulation: a flickering web of purple gas, white flares of starlight, and glowing yellow oxygen atoms swirling across the screen. It was the Milky Way’s origin story, not as a single galaxy, but as thousands of tiny ones colliding and merging over billions of years. For three years, Katz and his team fed physics into supercomputers—gravity, radiation, chemistry—and let time unfold from 180 million years after the Big Bang. What emerged was the most detailed model yet of how our home galaxy came to be.
We can’t travel back in time to see the early universe, so scientists build digital universes instead. The project, called MEGATRON, lets researchers watch how gas cooled, stars ignited, and galaxies crashed together. "The very big bursts are catastrophic star formation events, typically caused by instabilities or when a galaxy merges," Katz explains. These explosions heated the gas, which then cooled again, sparking new waves of stars—a cycle that shaped everything we see today.
The simulation tracked thousands of small systems, far more than any previous model. Some were blazing with newborn stars; others were already dying, filled only with black holes or dark gas. One surprising find: some early 'galaxies' had no stars at all, yet still glowed—possibly powered by ancient black holes or pure hydrogen clouds. Another breakthrough solved a long-standing mystery. In faint dwarf galaxies today, iron levels don’t drop with size as expected—they stay roughly the same. MEGATRON shows why: the first stars, made only of hydrogen and helium, exploded in rare supernovae that flooded small galaxies with extra iron, changing their chemistry forever.
Now, with data from the James Webb Space Telescope streaming in, scientists can compare real observations to this virtual Milky Way. If they match, it means we’re on the right track to understanding cosmic dawn. And if not, it tells us where our physics might need fixing. Either way, we’re learning what kind of place our galaxy once was—and how chaos gave rise to order.
"For the first time, we can directly predict what the early Milky Way would have looked like to telescopes like Hubble or the James Webb Space Telescope," said Katz. That window into the past is now open.