Our galaxy may have begun its history in a much more fragmented form than its current disk.
A team of researchers led by Harley Katz used data from the MEGATRON project, a cosmological simulation, to follow a region destined to form a galaxy comparable to the Milky Way. The calculation begins about 180 million years after the Big Bang and follows nearly two billion years of evolution.
Artist’s view of the Milky Way showing its disk and central bar.
Credit: NASA/JPL-Caltech/R. Hurt — public domain.
The model evolves gravity, gas, radiation and chemistry according to the selected physical laws. The researchers then check whether the result resembles the galaxies actually observed.
At first, the simulated region brings together thousands of small galactic systems. Some rapidly form stars, others have very few, and some consist mostly of gas.
Over time, these small systems move closer together and merge. A much more massive galaxy gradually takes shape. About 12 billion years ago, the model can already produce a rotating disk, despite the collisions between galaxies that are still frequent.
MEGATRON also predicts unusual objects: galaxies with no visible stars that can nevertheless emit light. Their gas may radiate after the disappearance of ancient stars, or even before a lasting stellar population has formed.
The model directly calculates what these young galaxies would look like when viewed by telescopes such as Hubble or James Webb. The main study compiles more than 175,000 simulated spectra. A spectrum distributes light according to its wavelength and provides information about gas and stars.
These results remain those of a model, not proof that our galaxy followed exactly this history. Some assumptions about stars and their production of elements still limit the calculations. Comparing them with observations could help identify what is missing.
The MEGATRON project is expected to continue until 2030. A new generation of simulations is planned to use 40 million hours of computing time on British supercomputers. This will serve to increase precision and compare these scenarios more extensively with data from James Webb and ancient stars in our vicinity.