Self-interacting dark matter impact on pulsar timing array observations

Mergers of supermassive black holes are a favored process to explain stochastic gravitational waves seen by pulsar timing arrays, but they suffer from a long-standing "final parsec problem," which causes them to stall before reaching the stage of GW emission.  We show that dynamical friction with dark matter spikes can solve this problem, and produce softening of the GW spectrum at low frequencies, if the DM is self-interacting, with cross sections previously identified as ameliorating small scale structure problems of CDM.