Milky Way may have begun as thousands of galaxies, new simulations suggest

Scientists used supercomputers to simulate the early universe, revealing that the Milky Way may have started as thousands of smaller galaxies. The simulations, led by Harley Katz, show that the region now containing the Milky Way was a collection of galaxies, some producing stars and others filled with gas or containing dead stars and black holes. The model predicts that these galaxies merged over time to form the spiral disk we see today. The simulations, which took three years to run, are the most detailed of their kind and provide new insights into the formation of early galaxies and the elements they contain. The simulations include detailed computations of non-equilibrium physics, which helps in understanding how the early universe evolved. The results show that the Milky Way may have had galaxies with no stars but still shining, possibly formed from stellar explosions or direct collapse into black holes. The simulations also address a long-standing puzzle in astrophysics, where smaller and fainter galaxies have less iron, but this trend breaks down in very faint systems. The simulations suggest that Population III stars, which are old and made of only hydrogen and helium, could have produced more iron than other supernovae, and their presence could explain this phenomenon. The simulations also show that the Milky Way could have formed a rotating disk with heavy elements and dust, and that the collision of two galaxies left a trail of stars. The study highlights the importance of including non-equilibrium physics in simulations to better understand the early universe.

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