In the Dark

Today we published four papers at the Open Journal of Astrophysics all related to the Megatron Project which is co-led by Martin Rey of the University of Bath (UK), Harley Katz of the University of Chicago (USA) and Corentin Cadiou of the Institut d’Astrophysique de Paris in France. I will include this quartet in my regular weekly update on Saturday but there is a press release accompanying these publications so I thought I’d splash them a bit here too.

I’ll show the overlays on Saturday but in the meantime here are some pretty graphics from three of the papers:

In no particular order the four papers are:

MEGATRON: Reproducing the Diversity of High-Redshift Galaxy Spectra with Cosmological Radiation Hydrodynamics Simulations

MEGATRON: how the first stars can create an iron metallicity plateau in the smallest dwarf galaxies

MEGATRON: the impact of non-equilibrium effects and local radiation fields on the circumgalactic medium at cosmic noon”

MEGATRON: The Physical Origins of Steep UV Slopes at high redshift

The Press Release from the University of Bath is reproduced below. A Press Release in French can be found here.

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New simulations connect the first stars to cosmic fingerprints still visible today

International MEGATRON project links space telescope observations of the infant Universe with the chemical fossil record of the Milky Way.

Researchers have used some of the most detailed simulations yet of the early Universe to investigate how the first stars and galaxies formed.

Led by researchers at the University of Bath, alongside collaborators at the University of Chicago in the US and the Institut d’Astrophysique de Paris in France, the MEGATRON project uses advanced simulations to explore how the first stars and galaxies lit up the previously dark cosmos and enriched it with the chemical elements that would later become the building blocks of everything around us.

Published today in the Open Journal of Astrophysics, four studies from the MEGATRON project combine cutting-edge cosmological simulations with sophisticated models of radiation, chemistry and galaxy formation. Together, these constitute the collaboration’s first substantial body of published results, with further papers expected to follow.

The findings from the study of the first stars show that accurately capturing the interplay between starlight, gas and newly forged elements is essential for connecting two previously separate views of the early Universe: observations of young galaxies by the James Webb Space Telescope (JWST) and the chemical clues preserved in ancient stars in and around the Milky Way – the galaxy that contains our Solar System.

JWST provides a direct view of galaxies in the infant Universe, while ancient stars act as a fossil record of cosmic history. By studying the chemical fingerprints of these ancient stars, astronomers can reconstruct the properties of the first stars and trace how they enriched the cosmos with the first chemical elements.

The simulations follow the evolution of a young galaxy that will eventually grow into a system similar in mass to the Milky Way. Using advanced computer models that simultaneously track the movement of gas, the propagation of starlight and the evolution of chemical concentrations, the team investigated how stars shape the gas in and around galaxies over billions of years.

The study suggests that simplified models may underestimate the influence of stellar radiation and complex chemical processes on the gas surrounding galaxies. By modelling these effects at exceptionally high resolution, the team resolved structures in the gas that are not captured by simpler models, helping to improve predictions for current and future astronomical observations.

A direct glimpse of the infant cosmos

Dr Martin Rey from the Department of Physics at the University of Bath and a lead contributor to the MEGATRON collaboration, said: “The James Webb Space Telescope gives us a direct glimpse of the infant cosmos, while stellar archaeology allows us to study the relics of those earliest times in our own Galactic neighbourhood. MEGATRON provides a physical bridge between the two.”

The simulations begin with pristine gas containing no heavy elements, mirroring conditions shortly after the Big Bang. They then follow the birth of the first stars, the radiation they emit, the supernova explosions that mark their deaths and the dispersal of newly forged elements into subsequent generations of stars and galaxies.

Understanding this process is central to one of astronomy’s most fundamental questions: where the elements that make up today’s Universe came from.

Dr Rey said: “The elements that make our world and life possible – carbon, oxygen, iron and many others – were forged by stars. To understand where those elements came from, we need to understand how the first stars formed and enriched their surroundings. MEGATRON allows us to test these ideas directly by comparing detailed simulations with observations from JWST and the chemical fingerprints preserved in ancient stars.”

Looking ahead, the team plans to use MEGATRON to strengthen links between theory and emerging observational data. As JWST continues to transform our understanding of the earliest galaxies, large-scale stellar surveys will provide increasingly detailed information about ancient stars in and around the Milky Way.

Dr Rey and his colleagues at Bath are already developing the next generation of simulations. The project has been awarded 40 million processor hours on the UK’s national supercomputers, equivalent to running five million laptops in parallel for a year. These resources will enable simulations with higher resolution and more complete physical models, allowing even more direct comparisons with JWST observations and the chemical fossil record preserved in ancient stars.

“MEGATRON provides a common physical framework for interpreting two of astronomy’s most exciting new datasets: JWST’s view of the earliest galaxies and the stellar fossil record,” said Dr Rey. “Together, these complementary observations allow us to test competing models of the first stars in ways that weren’t previously possible.”

The MEGATRON project started in 2023 and is scheduled to run until 2030.