CHICAGO — The neighborhood that became the Milky Way may have started as thousands of smaller galaxies, some bursting with stars and some shining with no stars at all, according to a set of simulations that took three years to run.

Harley Katz, an assistant professor of astronomy and astrophysics at the University of Chicago, led the project, named MEGATRON. Six papers are published in The Open Journal of Astrophysics. The model follows the first several billion years of a galaxy like ours, from about 180 million years after the Big Bang through roughly two billion years of evolution.

"What does the Milky Way look like at what we call cosmic dawn?" Katz said. "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."

The method is the standard one for a past that cannot be visited. "Essentially, we put in all of the physics we think is relevant—gravity, hydrodynamics, radiation, chemistry, etc.—and then let it evolve and see if it reproduces what we actually see when we look around us today," Katz said. The team built the runs to take in what........

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