Globular clusters contain hundreds of thousands to millions of stars orbiting galaxies like the Milky Way. Unlike galaxies, they lack dark matter and host stars that are unusually similar in age and chemical makeup. Their uniformity has puzzled astronomers since their discovery in the 17th century.
To solve this mystery, Surrey researchers developed ultra-high-resolution simulations known as EDGE, which traced the 13.8-billion-year history of the cosmos in remarkable detail. These simulations showed how globular clusters form naturally, without the need for special assumptions, and also revealed a new class of stellar system, dubbed "globular cluster-like dwarfs," which share features of both clusters and dwarf galaxies.
"These simulations add crucial context to how globular clusters arise," said Dr Ethan Taylor, Postdoctoral Research Associate at Surrey and lead author of the study. "The fact that they appeared in EDGE without being programmed in makes the simulations more realistic. Discovering a new class of object was a thrilling bonus, especially as we may already have identified several candidates in our own Milky Way."
The team, which included collaborators from Durham University, the University of Bath, the University of Hertfordshire, Carnegie Observatories, the American Museum of Natural History, Lund University and the University of Barcelona, relied on the UK's DiRAC National Supercomputer. Simulations at this scale would take decades to run on standard computing hardware.
Unlike conventional dwarf galaxies, which contain vast quantities of dark matter, the newly identified globular cluster-like dwarfs resemble normal star clusters yet still hold significant amounts of dark matter. This hidden feature suggests some known systems, such as the Milky Way satellite Reticulum II, could already fit the category and offer new ways to study both dark matter and the earliest stellar generations.
"The EDGE project aimed to build the most detailed model of the smallest galaxies, covering the universe's full history while resolving details like individual supernovae," said Professor Justin Read, Chair of Astrophysics at Surrey. "At a resolution of just 10 light years, we have shown globular clusters can form through at least two different channels, both independent of dark matter."
Astronomers now plan to use facilities such as the James Webb Space Telescope and upcoming spectroscopic surveys to confirm whether globular cluster-like dwarfs exist in reality. If so, they could become key targets for probing dark matter and identifying the earliest, pristine stars in the universe.
Research Report:The emergence of globular clusters and globular-cluster-like dwarfs
Related Links
University of Surrey
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