Three Birds with One Stone: Core-Collapsed SIDM Halos as the Common Origin of Dense Perturbers in Lenses, Streams, and Satellites

TL;DR

The paper tackles the puzzle of unusually dense, $\sim 10^6\,M_\odot$ substructures observed in strong lensing, Milky Way satellites, and stellar streams, which challenge standard CDM expectations. By comparing the inferred density profiles of JVAS B1938+666 (Pseud-Jaffe), Fornax 6, and the GD-1 perturber with SIDM halos evolved in a Milky Way–like potential under cross sections $\sigma/m = 0,30,50,100\, {\rm cm^2/g}$, the authors test the core-collapse hypothesis. The results show the three objects are compatible with core-collapsed SIDM halos, while CDM profiles fail to reach their central densities, suggesting a unified SIDM origin. This supports velocity-dependent SIDM models and motivates targeted, system-specific simulations and observations to break degeneracies and provide decisive tests of the SIDM interpretation.

Abstract

We show that core-collapsed self-interacting dark matter halos of mass $\sim 10^6\,{M_\odot}$, originally simulated to explain the dense perturber of the GD-1 stellar stream, also reproduce the structural properties inferred for the dense perturber detected in the strong lensing system JVAS B1938+666 from radio observations. Furthermore, these halos are sufficiently compact and dense to gravitationally capture field stars in satellite galaxies of the Milky Way, providing a natural explanation for the origin of Fornax 6, a stellar cluster in the Fornax dwarf spheroidal galaxy. Our results demonstrate that observations of halos with similar masses but residing in different cosmic environments offer a powerful and complementary probe of self-interacting dark matter.

Figures (1)

• Figure 1: Density profiles of the JVAS B1938+666 strong-lensing perturber from radio observations Powell:2025rmj (solid cyan), the Fornax substructure Penarrubia:2024vms (solid blue), and the GD-1 stream perturber Bonaca:2018fek (shaded gray). For comparison, we show simulated halo density profiles for $\sigma/m=0\,{\rm cm^2/g}$ (CDM, dashed black), $30\,{\rm cm^2/g}$ (dashed amber), $50\,{\rm cm^2/g}$ (dashed orange), and $100\,{\rm cm^2/g}$ (dashed pink), as well as the initial condition before tidal evolution (dotted black), from Zhang:2024fib.