Speaker
Description
The classical Jeans instability states that baryonic perturbations grow only above the Jeans scale, while cold dark matter is unstable on all scales. In this talk, I will show that the relative drift between baryons and dark matter after decoupling fundamentally alters this picture.
When the projected DM drift is subsonic, a new resonant gravitational instability – the Shalaby‑Broderick instability – drives exponentially growing sound waves in the baryons, with growth rates exceeding the intrinsic DM growth rate. In baryon‑dominated environments, the instability also opens a stable window between the Jeans scale and the resonant scale.
I will demonstrate that the associated timescales range from years to tens of millions of years across diverse astrophysical systems – planets, stars, molecular clouds, galaxies, and galaxy clusters – typically much shorter than their ages. On cosmological scales, the instability enhances baryon density perturbations for appropriately oriented modes while suppressing those aligned with the DM stream, leaving a distinct anisotropic imprint on the 21 cm signal and the distribution of early galaxies.
Crucially, this resonant mechanism provides a fundamentally new way to detect dark matter directly – not through particle‑particle collisions, but through the gravitational resonance between baryonic sound waves and Doppler‑shifted DM modes. This opens observational windows via seismic vibrations (Earth, Moon, ice sheets), galactic spiral structure, and pulsar timing arrays – turning the relative motion of dark matter from a nuisance into a powerful diagnostic tool.