Superfluid turbulence and pulsar glitch statistics

Abstract

Experimental evidence is reviewed for the existence of superfluid turbulence in a differentially rotating, spherical shell at high Reynolds numbers ($\Rey\gsim 10^3$), such as the outer core of a neutron star. It is shown that torque variability increases with $\Rey$, suggesting that glitch activity in radio pulsars may be a function of $\Rey$ as well. The $\Rey$ distribution of the 67 glitching radio pulsars with characteristic ages $\tau_c \leq 10^6$ {\rm yr} is constructed from radio timing data and cooling curves and compared with the $\Rey$ distribution of all 348 known pulsars with $\tau_c \leq 10^6$ {\rm yr}. The two distributions are different, with a Kolmogorov-Smirnov probability $\geq 1 - 3.9 \times 10^{-3}$. The conclusion holds for (modified) Urca and nonstandard cooling, and for Newtonian and superfluid viscosities.