Formation of cosmic structure by Doppler instability

Abstract

A new mechanism is described which can create an instability in homogeneous gaseous matter at very low density. When an isotropic background radiation field has, near an electronic resonance (such as the hydrogen Lyman-α line), a spectral feature for which photon occupation number increases with frequency, moving atoms increase their speed by taking energy from the photon distribution. In a cosmological setting, a sufficiently intense spectral feature can interact with neutral atomic gas, after recombination, to generate protogalactic perturbations of the scale and magnitude needed to explain large-scale cosmic structure.