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New simulations reveal an unexpected class of star systems
High-resolution cosmological simulations run by the University of Surrey and collaborators have identified a previously unrecognized category of ancient star systems that may already be hiding in the Milky Way. The study, published in Nature, uses the EDGE simulation suite to trace 13.8 billion years of cosmic history at resolutions fine enough to capture the impact of individual supernovae. The results offer a unified view of how globular clusters form and predict a transitional population — “globular cluster-like dwarfs” — that blend properties of classical globular clusters and dwarf galaxies.
A globular cluster (white concentration of stars) naturally emerges in the high-resolution EDGE simulations. These simulations also predict the existence of a new class of object: globular cluster-like dwarfs. These new objects form similarly to globular clusters, but in their own dark matter halo. The nearby Reticulum II dwarf galaxy may be such an object that has been hiding in plain sight in our cosmic backyard. If so, it promises unprecedented constraints on the nature of dark matter and a new place to hunt for the first metal-free stars.
Scientific background and simulation approach
Globular clusters are compact, gravitationally bound collections of hundreds of thousands to millions of stars orbiting larger galaxies. They are among the oldest stellar systems known and are characterised by tight stellar packing, nearly uniform stellar ages, and low chemical diversity. These properties have made their origin a long-standing problem in astrophysics, in part because globular clusters generally show little or no evidence for surrounding dark matter — unlike dwarf galaxies, which are strongly dark matter dominated.
To explore formation pathways, the EDGE simulations model galaxy formation at ultra-high resolution across cosmic time using the UK DiRAC National Supercomputer facility. The team included collaborators from several institutions worldwide and ran simulations that would take decades on typical consumer hardware. By resolving scales of about 10 light-years, EDGE captures localized feedback from single supernovae and the dynamics that can lead to compact stellar systems forming inside different dark matter environments.
Key findings: multiple formation routes and a new hybrid class
EDGE shows that globular clusters can arise via at least two formation channels. Some clusters form in dense gas regions that become self-bound and lose any surrounding dark matter, producing the classical, dark-matter-poor globular clusters we observe. Other compact systems form inside their own small dark matter halos but share the stellar compactness and old ages typical of globular clusters. The latter are the predicted "globular cluster-like dwarfs": observationally compact and cluster-like, yet embedded within a significant dark matter halo.
This subtle structural difference matters. If these hybrid objects exist in the real Universe, they could have been catalogued as ordinary globular clusters by telescopes, masking their dark matter content. Several Milky Way satellites — notably the ultra-faint Reticulum II — are highlighted as candidate globular cluster-like dwarfs. Confirming their dark matter content would provide a rare laboratory to test dark matter models and to search for extremely metal-poor (or metal-free) stars from the first stellar generations.
Observational prospects and implications
The next steps are targeted observations using facilities such as the James Webb Space Telescope and forthcoming deep spectroscopic surveys. High-precision kinematic data and resolved stellar spectroscopy can distinguish a dark-matter-dominated system from a purely stellar cluster. Establishing a population of globular cluster-like dwarfs would influence theories of star cluster formation, the role of feedback in small halos, and strategies to find primordial stars.
Expert Insight
Dr. Ethan Taylor (University of Surrey) notes that EDGE produced these systems without inserting special prescriptions to force their formation, increasing confidence that the objects are a natural outcome of galaxy formation physics. Professor Justin Read adds that the simulations' 10 light-year resolution was critical to resolving the physical processes that differentiate cluster formation channels.
Conclusion
The EDGE simulations provide a more complete picture of how compact stellar systems form and predict a transitional class — globular cluster-like dwarfs — that could already be present among Milky Way satellites. Confirming these objects observationally would open new tests of dark matter and new search fields for the Universe’s earliest stars, resolving aspects of a centuries-old astronomical puzzle.
Source: scitechdaily
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