A Microphysical Probe of Neutron Star Interiors: Constraining the Equation of State with Glitch Dynamics

TL;DR

This work develops a microphysical, three-component glitch model that ties neutron-star interior physics to observable glitch dynamics by combining a unified RMF equation of state, crustal pinning and Kelvin-wave–driven mutual friction, and core electron-scattering friction. Using MCMC fits to the 2016 Vela glitch timing residuals, the study finds a weak core friction with $\mathcal{B}_{core} \sim 10^{-4}$ and a weak to moderate crustal entrainment ($f_e \approx 0.7$), while constraining the Vela mass to $1.05$–$1.65\,M_\odot$ across two EOS families (DD-ME2 and PKDD). The results show EOS-dependent trends in the crustal angular-momentum reservoir $I_{sf}/I$ and in the glitch rise/overshoot morphology, with PKDD yielding monotonic $L_0$-dependencies and DD-ME2 exhibiting nonmonotonic behavior; overall, the analysis supports electron scattering as the dominant core friction mechanism and highlights the role of symmetry-energy slope in shaping glitch rise. The study demonstrates the potential of high-cadence timing to further constrain NS interior composition and microphysical processes, and it discusses implications for anti-glitches and multi-messenger timing in the future.

Abstract

Glitches in neutron stars originate from the sudden transfer of angular momentum between superfluid components and the observable crust. By modeling this glitch dynamics, including vortex motion, mutual friction, and angular momentum exchange, we can probe the dense matter equation of state. We match theoretical predictions of glitch rise times, overshoot patterns, and relaxation timescales to the well-documented observations of the 2016 Vela glitch. Our model incorporates microphysical parameters such as the mutual friction coefficient $\mathcal{B}$, which in the core arises from electron scattering off magnetized vortices, and in the crust from Kelvin wave excitation during vortex-lattice interactions. Our Markov Chain Monte Carlo analysis of the timing residuals reveals detailed glitch dynamics: the crustal superfluid couples on timescales of $\sim100$ seconds, the core exhibits overshoot behavior due to strong central behavior, and the inner crust shows weak entrainment, with $\sim70\%$ of free neutrons remaining superfluid. The modeled rise times are consistent with the observed upper limit of 12.6 seconds, and the observed overshoot requires strong crustal friction but weak core friction, supporting a spatially varying $\mathcal{B}$.These findings highlight the importance of microphysical modeling and demonstrate the potential of future high-cadence timing observations to further constrain the internal dynamics and composition of neutron stars.

Figures (12)

• Figure 1: Radial profiles of pinning energy $E_\mathrm{p}$ in the inner crust of a $1.4M_{\odot}$ neutron star. (a) Dependence on the symmetry energy slope $L_0$ for the PKDD interaction, with no entrainment ($f_{\mathrm{e}}=1.0$). The gray shaded region uses a linear scale for $-1<E_{\mathrm{p}}<1$ MeV. (b) Dependence on the entrainment factor $f_{\mathrm{e}}$ for PKDD with $L_0=40$ MeV. Stronger entrainment (lower $f_{\mathrm{e}}$) significantly suppresses pinning energy in the bottom of the crust.
• Figure 2: Radial profiles of mutual friction coefficients $\mathcal{B}_{\mathrm{crust}}$, which derived from Fig. \ref{['fig:Ep_crust']} with unchanged settings, in the inner crust.
• Figure 3: Mutual friction coefficients $\mathcal{B}_{\mathrm{core}}$ as a function of normalized radial distance $r/R_{\mathrm{cc}}$ in the core for PKDD with different $L_0$ and fixed $1.4M_{\odot}$ NS mass. The shaded region indicates the range of $\mathcal{B}_{\mathrm{core}}$ for $\mathcal{M}_{p}^*/\mathcal{M}_{p} = 0.5$--$0.7$, with the upper and lower boundaries corresponding to $\mathcal{M}_{p}^*/\mathcal{M}_{p} =0.5$ and $\mathcal{M}_{p}^*/\mathcal{M}_{p} = 0.7$, respectively.
• Figure 4: Crustal superfluid angular velocity ($\Omega_{\mathrm{sf}}$) as a function of the normalized crust radial distance $(\tilde{r}-R_{\mathrm{cc}})/(R_{\mathrm{oi}}-R_{\mathrm{cc}})$ and time $t$ following a glitch. The results are calculated with PKDD with $L_0=40$ MeV. The entrainment $f_{\mathrm{e}}=1.0$ and NS mass $1.4M_{\odot}$ are adopted.
• Figure 5: Core superfluid angular velocity ($\Omega_{\mathrm{core}}$) as a function of the normalized crust radial distance $\tilde{r}/R_{\mathrm{cc}}$ and time $t$ following a glitch. The results are calculated with PKDD with $L_0=40$ MeV. The entrainment $f_{\mathrm{e}}=1.0$ and NS mass $1.4M_{\odot}$ are adopted. The gray solid line indicates the frequency of the "crust" component at $t=96$ s.