The research, led by Associate Professor Dr Azadeh Fattahi of the Oskar Klein Centre (OKC) in Stockholm with the LYRA collaboration, in partnership with Durham University and the University of Hawaii, also reveals what the Universe's earliest climate was like - including radiation levels and their influence on where and whether stars formed.
"In this work we presented a brand-new suite of cosmological simulations focused on the faintest galaxies in the universe, with an unprecedented resolution. These are by far the largest sample of such galaxies ever simulated at these resolutions," Fattahi said.
Dwarf galaxies form in small dark matter halos predicted by the standard model of cosmology. The faintest examples are extreme in both size and fragility, lying at the boundary of knowledge about galaxy formation and dark matter.
"The smallest galaxies are called ultra-faint dwarf galaxies, which are a million times less massive than the Milky Way or even smaller. Due to their small size these galaxies have proven very difficult to model and simulate," Fattahi said.
Study lead Shaun Brown, who worked at OKC and Durham University, used an agricultural analogy to describe the team's approach. "A useful analogy is to plants and crops and how the way they grow is sensitive to the weather conditions. In the same way that the yield of a crop in summer can indirectly tell you a lot about what the weather in spring must have been like, the properties of faint dwarf galaxies today can tell us a lot about the conditions, or weather, of the universe at a much earlier time."
Beyond reproducing faint dwarf galaxies, the simulations suggest these local objects can act as probes of the universe's earliest climate. The team tested two different assumptions about the properties of the early Universe when it was less than 500 million years old, examining the effects on galaxy properties today - when the universe is 13 billion years old.
"We found that these small ultra-faint galaxies are very sensitive to these changes, while more massive galaxies, like our Milky Way, don't really care. For the smallest galaxies, early conditions can decide whether they become visible galaxies - or remain starless dark matter halos," Brown said.
That sensitivity creates a clear path to testing early-universe physics with upcoming telescope surveys. The Vera C. Rubin Observatory is expected to find many more ultra-faint dwarfs around the Milky Way, potentially providing a near-complete census of Milky Way satellite galaxies - and these simulations indicate that census may carry information far beyond the local neighbourhood.
The findings are also relevant in light of recent James Webb Space Telescope discoveries of unexpectedly massive and bright galaxies in the early universe. Ultra-faint dwarfs may provide an additional window into understanding those surprises.
Running the simulations took more than six months and generated approximately 300 terabytes of data, requiring updates to older algorithms. The bulk of the computational work was performed on the COSMA 8 supercomputer, hosted by Durham University's Institute for Computational Cosmology on behalf of the UK's DiRAC High Performance Computing Facility.
Future work with the simulation suite will address open questions including the location of the universe's very first generation of stars, and what the properties of ultra-faint dwarf galaxies can reveal about the nature of dark matter.
Research Report:LYRA ultra-faints: The emergence of faint dwarf galaxies in the presence of an early Lyman-Werner background
Related Links
Royal Astronomical Society
Stellar Chemistry, The Universe And All Within It
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