Megatron simulations assemble a Milky Way-like galaxy from thousands of small ones

The count describes a model galaxy. Megatron traces how a galaxy like ours comes together ^[19]. The thousands of small galaxies, of many sizes and shapes, are what its Milky Way region holds in the universe's first 2 billion years, before they collide and merge ^[1]. The coverage does not say how many Milky Way-like regions the team simulated. It also does not say whether the new galaxies reproduce the bright early objects and Little Red Dots that the researchers cited as reasons to update the models ^[4].

I think the more useful result is the output format. Megatron follows gas, starlight and chemistry from 180 million to 2 billion years after the Big Bang, and it predicts the light signatures its virtual galaxies would give off ^[2]. JWST collects the same type of spectral data over a similar span of cosmic time. According to the team, that lets the simulation be checked directly against real observations to pinpoint what older models miss ^[3].

The authors do not claim a full match ^[16]. "But there are also things we're not getting right, which is interesting too," said Harley Katz, an assistant professor of astronomy and astrophysics at the University of Chicago ^{[11] [14]}. He followed with a question, "what are the parts we're still missing?" ^[12], and added: "That can lead you into new directions and new questions." ^[13]

The chemistry is a second check. The runs track how the first stars formed, died and forged new elements. Those predictions can then be compared both with JWST observations of early galaxies and with the chemical traces left in ancient stars ^[5]. "Together, these complementary observations allow us to test competing models of the first stars in ways that weren't previously possible," said Martin Rey, a theoretical astrophysicist at the University of Bath ^{[6] [15]}.

Katz also tied the early physics to the present. "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," he said ^[10]. The simulation covers 1.82 billion years of that history, from 180 million to 2 billion years after the Big Bang ^[18].