Pulsar Glitches: The Crust is not Enough

Pulsar glitches are traditionally viewed as a manifestation of vortex dynamics associated with a neutron superfluid reservoir confined to the inner crust of the star. In this Letter we show that the nondissipative entrainment coupling between the neutron superfluid and the nuclear lattice leads to a less mobile crust superfluid, effectively reducing the moment of inertia associated with the angular momentum reservoir. Combining the latest observational data for prolific glitching pulsars with theoretical results for the crust entrainment, we find that the required superfluid reservoir exceeds that available in the crust. This challenges our understanding of the glitch phenomenon, and we discuss possible resolutions to the problem.

Figure 1

The accumulated $\sum _i\Delta {\Omega }_p^i/{\Omega }_p$ ($\times {10}^{-9}$) as a function of the modified Julian date for the x-ray pulsar J0537-6910 and the Vela pulsar (B0833-45). The fits that lead to the slopes $(\mathcal{A}$) listed in Table  are shown as straight lines.

Figure 2

Same as Fig. 1, for pulsars with a smaller number of large glitch events.

Figure 3

The moment of inertia ratio $I_n/I_0$ as a function of the stellar mass for the models from Ref. 15 (APR) and Ref. 22 (SLy). If the glitches in the Vela pulsar are to be explained by the crust superfluid alone, then the moment of inertia ratio must satisfy $I_n/I_0\gtrsim 0.016\times (⟨m_n^{*}⟩/m_n)\approx 0.07$ (gray region, with entrainment according to Ref. 10; we also show the constraint when entrainment is not accounted for, as in Ref. 7.)