Physical Society Colloquium

The nature of dark matter with stellar streams in the LSST era

Ana Bonaca

Carnegie Theoretical Astrophysics Center

Astrophysical searches for the particle nature of dark matter have been rapidly expanding. Stellar streams, long thin filaments of stars produced by tidal dissolution of star clusters, are especially sensitive tracers of dark matter. Based on a Fisher-information calculation, we expect that the current data on the known Milky Way streams should constrain the radial profile and the shape of the inner halo to a precision of a few percent. In addition, numerical experiments suggest stellar streams retain a detailed record of the matter field on small scales, down to halo masses of ~10⁶ Msun (wavenumber k~100 h/Mpc). Excitingly, observations of several stellar streams indicate dynamical perturbation consistent with dark matter substructure, although alternative explanations have not been ruled out fully. Upcoming facilities like the Vera Rubin Observatory's LSST (first light Jul 2025) and the Via Project (first light Dec 2026) will provide more detailed observations of the structure and kinematics for a hundred stellar streams in the Milky Way halo. I will discuss how these data will isolate dark matter signals in stellar streams, constrain the linear matter power spectrum on scales below the threshold for galaxy formation, to ultimately explore dark matter particle candidates in the mass regime of <~25keV.