The Milky Way galaxy in its infancy did not resemble the vast spiral disk we see today. Rather, according to a new computer simulation, it arose from a turbulent cosmic environment teeming with thousands of small galactic systems that interacted and gradually merged during the first billions of the universe's existence.
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Katz says the simulation allows, for the first time, direct prediction of how the early Milky Way might have appeared to telescopes such as Hubble and James Webb, which allows for comparison of theoretical models with ancient galaxies observed by telescopes today.
Instead of assuming that the Milky Way began as a single, uniform object, the simulation tracked thousands of smaller systems that interacted, expelled gas between them, and eventually merged. These objects were incredibly diverse; some experienced intense star formation, some were rich in gas, while others had ceased producing stars or were on the path to doing so.
The scientists incorporated a wide range of physical processes into the model, including gravity, gas dynamics, radiation, chemistry, and stellar evolution. They then allowed the model to evolve to see how well it could produce properties similar to those scientists currently observe in the nearby universe.
As cosmic time passed, the fragmented environment became more regular, and repeated mergers and gas flows helped build larger structures, eventually leading to a galactic disk resembling the present-day Milky Way.
One of the strangest predictions of the Megatron is the possibility of objects that appear in observations like galaxies, even though they do not contain stars. Some of them may have once had stars before they exploded or collapsed, leaving behind black holes, while other systems may be composed mainly of gas.
This result is of particular importance when interpreting the extremely distant objects observed by the James Webb Space Telescope, as the simulation indicates that the discovery of a light source in the early universe does not necessarily mean that it is a conventional galaxy full of stars.
The fingerprints of the first stars in the universe
The simulation also offers a possible explanation for the unusual chemical composition of some faint galaxies. Normally, the abundance of iron decreases as the mass of a galaxy decreases, but this relationship appears less pronounced in the faintest known galaxies.
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