Background Pulsar glitches—the sudden spin-up in the rotational frequency of a neutron star—suggest the existence of an angular-momentum reservoir confined to the inner crust of the neutron star .
Large and regular glitches observed in the Vela pulsar have originally constrained the fraction of the stellar moment of inertia that must reside in the solid crust to about 1.4 % .
However , crustal entrainment—which until very recently has been ignored—suggests that in order to account for the Vela glitches , the fraction of the moment of inertia residing in the crust must increase to about 7 % .
This indicates that the required angular momentum reservoir may exceed that which is available in the crust .

Purpose We explore the possibility that uncertainties in the equation of state provide enough flexibility for the construction of models that predict a large crustal thickness and consequently a large crustal moment of inertia .

Methods Moments of inertia—both total and crustal—are computed in the slow-rotation approximation using a relativistic mean field formalism to generate the equation of state of neutron-star matter .

Results We compute the fractional moment of inertia of neutron stars of various masses using a representative set of relativistic mean-field models .
Given that analytic results suggest that the crustal moment of inertia is sensitive to the transition pressure at the crust-core interface , we tune the parameters of the model to maximize the transition pressure , while still providing an excellent description of nuclear observables .
In this manner we are able to obtain fractional moments of inertia as large as 7 % for neutron stars with masses below 1.6 solar masses .

Conclusions We find that uncertainties in the equation of state of neutron-rich matter are large enough to accommodate theoretical models that predict large crustal moments of inertia .
In particular , we find that if the neutron-skin thickness of ^ { 208 } Pb falls within the ( 0.20-0.26 ) fm range , large enough transition pressures can be generated to explain the large Vela glitches—without invoking an additional angular-momentum reservoir beyond that confined to the solid crust .
Our results suggest that the crust may be enough .