The large cores of dark matter and globular clusters in AS1063: Possible evidence of self-interacting dark matter, or not

Instituto de Física de Cantabria (CSIC-UC), Avda. Los Castros s/n. 39005 Santander, Spain

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Received: 26 February 2026
Accepted: 15 June 2026

Abstract

Deep JWST images of AS1063 have revealed tens of thousands of globular clusters in the galaxy cluster AS1063. When compared with the lensing model based on the same JWST data, the distribution of globular clusters is shown to closely trace the distribution of lensing mass (mostly composed of dark matter). Interestingly, the distributions of dark matter and globular clusters are both characterized by large central cores. However, the size of the core in the distribution of globular clusters is about half the size the core in the dark matter distribution. We argue that the standard cold dark matter and fuzzy dark matter models struggle to explain these large cores. Meanwhile, self-interacting dark matter, with a velocity-dependent cross-section, combined with core stalling, offers a natural explanation for the existence of these cores in cases where σ_SI ≈ 0.3 cm² g⁻¹ in galaxy cluster halos. However, we also discuss how the lack of hydrodynamical N-body simulations capable of resolving globular clusters in galaxy cluster-scale halos hinders our ability to completely rule out the standard noncollisional dark matter scenario. Future high-resolution hydrodynamical simulations of galaxy clusters, with several trillion particles and containing over a hundred thousand globular clusters, can provide the insights needed to transform the epistemic nature of dark matter into an ontological one.