Dark Matter Opens Its Arms express
The James Webb Space Telescope peered into the galaxy cluster AS1063 and spotted tens of thousands of globular clusters — dense stellar "knots" scattered throughout the cluster. Their positions matched the map of invisible mass, which is constructed from the bending of light from distant galaxies. This invisible mass is dark matter — a substance that doesn't shine but holds galaxies together with its gravity.
It turns out that both dark matter and globular clusters have an extensive "core" at the cluster's center — a region where density barely increases toward the middle. This core is twice as large for dark matter as for the clusters. Standard models, where dark matter doesn't collide with itself, cannot explain such a large core. But if dark matter particles occasionally interact with each other, the core emerges naturally.
What's missing are computer simulations that simultaneously reproduce both dark matter and globular clusters on the scale of an entire galaxy cluster. Calculations with trillions of particles are needed. If they confirm the picture, dark matter will cease to be just a hypothesis and will acquire concrete properties.
Original abstract
as written by the authors arXiv:2602.15940
Deep JWST images of AS1063 reveals 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 traces closely the distribution of lensing mass (mostly composed of dark matter). Interestingly, both the distributions of dark matter and globular clusters have large central cores. However the size of the core in the distribution of globular clusters is about half the size the core of the dark matter distribution. We argue that the standard cold dark matter and fuzzy dark matter models struggle to explain these large cores. Meanwhile, the self interacting dark matter with a velocity dependent cross section, combined with core stalling, offers a natural explanation to the existence of these cores if $$\sigma_{\rm SI}\approx 0.3$$ cm$$^2$$ g$$^{-1}$$ for galaxy cluster halos. But we also discuss how the lack of hydrodynamical N-body simulations capable of resolving globular clusters in galaxy cluster scale halos, hinders the possibility of ruling out the standard non-collisional 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 insight needed to transform the epistemic nature of dark matter into an ontological one
Globular clusters are among the oldest objects in the universe, often more than 10 billion years old.