The Resonant Gravitational instability from Baryon-Dark Matter relative Streaming

Abstract

The Jeans instability is a fundamental mechanism that explains how the initially almost uniform density of the early universe gave rise to collapsed structures—from molecular clouds and stars to galaxies and clusters. It also plays a key role in interpreting astrophysical probes such as the Lyman‑alpha forest seen in quasar spectra. In this talk, I will discuss how the classic Jeans instability is modified in the presence of dark matter (DM). I will show that when DM and baryons interact only through gravity and their relative drift is subsonic, a new resonant gravitational instability emerges—the Shalaby‑Broderick effect. I will outline efforts to identify observable signatures of this effect across a wide range of astrophysical systems, from planets and stars to galaxy clusters. On cosmological scales, probing this instability offers a direct test of the gravitational interaction between dark matter and baryons, and provides a unique window into DM perturbations on scales smaller than the baryonic Jeans scale—scales previously thought to be observationally inaccessible.