How do the Fermi bubbles accelerate cosmic rays without powerful shocks?

The Fermi bubbles—massive lobes of radiation extending 7–8 kiloparsecs above the galactic center—emit gamma rays and microwaves from relativistic electrons, but existing shock acceleration models struggle to explain the observed intensity. This work proposes that Rayleigh-Taylor instabilities in the bubble's expanding shell can accelerate cosmic rays directly, bypassing the need for powerful shocks and matching observations within feasible timescales.