Adiabatic evolution of hadronic neutron stars

Author(s)

Logoteta, Domenico, Constanzo, Francesco Zeno, Bombaci, Ignazio, Bernuzzi, Sebastiano, Perego, Albino, Radice, David

Abstract

In this paper we compute several structural properties of static and rotating neutron stars, considering both rigid and differential rotation. To this end, we use a finite-temperature beta-stable equation of state (EOS) extending the zero-temperature hadronic EOS derived by Fortin et al. (2017). We account for the formation of hyperons and the presence of a neutrino-trapped component. Our goal is to provide insights into the long-term evolution of a protoneutron star (PNS) formed after a core-collapse supernova (CCSN) or a remnant resulting from a binary neutron star merger (BNSM). The EOS is derived using a relativistic mean-field quantum many-body theory within the Hartree approximation. Coupling constants are determined using experimental data on hypernuclei and hypernuclear matter to better account for uncertainties in hyperon single-particle potentials. Our EOS models reproduce the typical features of cold neutron stars and PNSs for nucleonic and hyperonic compositions. In particular, they are consistent with measured masses (2.01 M_sun and 2.14 M_sun for PSR J0348+0432 and PSR J0740+6620) and dimensionless tidal deformabilities from GW170817. Thermal contributions act differently depending on composition and rotation state. Finally, our evolutionary scheme provides a simple way to interpret the long-term evolution of BNSM remnants or PNSs from CCSNe, complementing dynamical simulations unable to cover full evolutionary timescales.

Figures

Caption

Particles abundances ($X_i$) as function of the total baryonic numerical density for hyperonic matter. We show results for cold ($T = 0$) and neutrino-free matter, considering the case of density dependent (DD) coupling constants (dashed lines) and constant couplings (solid lines).

Caption

EOS for nucleonic matter (red line), hyperonic matter with DD coupling constants (black dashed line) and with constant couplings (black solid line).

Caption

Matter composition ($X_i$) as function of the baryonic density ($n_B$) in the case of a constant value of the entropy per baryon $S/A=2$ and considering neutrino trapped matter (dashed lines) and neutrino free matter (solid lines). We have adopted the case of constant couplings to set the hyperonic coupling constants.

Caption

Isoentropic EOSs for nucleonic matter (left panel), hyperonic matter (right panel) for $S/A=2$. The continuous line refer to $\nu$-free matter, the dashed one to $\nu$-trapped matter while the green dotted line refers to the $T=0$ $\nu$-free case.

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Mass radius relation for nucleonic matter (red line), hyperonic matter with constant couplings (black line) and DD couplings (black dashed line). Energy density on the $x$-axis is reported in units of $10^{15}$ {\rm g/cm}$^3$.

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Gravitational mass as function of the central energy density (in units of $10^{15}$ {\rm g/cm}$^3$) for nucleonic matter (left panel) and hyperonic matter (right panel) for several values of the entropy per baryon $S/A$. Dashed (solid) lines refer to neutrino trapped (free) matter. The green dotted line in both panels represents the zero temperature sequence.

Caption

In the left (right) panel we report the gravitational mass-central energy density relation at keplerian limit for nucleonic (hyperonic) matter for different values of $S/A$, considering neutrino free (solid lines) and neutrino trapped (dashed lines) matter. The green dotted line in both panels is the mass-central energy density relation for the cold nonrotating sequence.

Caption

Maximum gravitational mass as function of the maximum energy density for nucleonic matter considering two different differential rotation rates $\bar{A}$: $0.4$ (left panel) and $1$ (right panel). Results are reported for various values of $S/A$ for neutrino free (solid lines) and neutrino trapped (dashed lines) matter.

Caption

The same of Fig.\ \ref{fig7} but for hyperonic matter.

Caption

In the left panel we report the remnants evolution in the plane ($M_B-M_G$) in the case of pure nucleonic matter. The black solid line show the sequence of differentially rotating stars considering a rotational profile with $\overline{A}=1$, $S/A=2$ and $\nu$-trapped. The red dashed line is the sequence of rigid rotating stars at mass-shed limit with $S/A=2$ and $\nu$-trapped. The blue dot-dashed line is the sequence of rigid rotating stars at mass shed limit with $S/A=1$ and $\nu$-free matter. The green dotted line stands for the sequence of cold nonrotating neutron stars. In the right panel we show the angular momentum $J$ in units of $G M_\odot^2/c$ corresponding to the same equilibrium sequences reported in the left panel. The blue dotted lines are sequences of rigidly rotating stars with angular velocity $\Omega<\Omega_K$. Note $\Omega$ is reported in units of $10^{4} \frac{\rm rad}{\rm s}$. The black and red asterisks mark the gravitational mass of the two BNSM events GW170817 and GW190425 respectively. Note that the resulting baryonic mass is a prediction of our model.

Caption

In the left panel we report the remnants evolution in the plane ($M_B-M_G$) in the case of pure nucleonic matter. The black solid line show the sequence of differentially rotating stars considering a rotational profile with $\overline{A}=1$, $S/A=2$ and $\nu$-trapped. The red dashed line is the sequence of rigid rotating stars at mass-shed limit with $S/A=2$ and $\nu$-trapped. The blue dot-dashed line is the sequence of rigid rotating stars at mass shed limit with $S/A=1$ and $\nu$-free matter. The green dotted line stands for the sequence of cold nonrotating neutron stars. In the right panel we show the angular momentum $J$ in units of $G M_\odot^2/c$ corresponding to the same equilibrium sequences reported in the left panel. The blue dotted lines are sequences of rigidly rotating stars with angular velocity $\Omega<\Omega_K$. Note $\Omega$ is reported in units of $10^{4} \frac{\rm rad}{\rm s}$. The black and red asterisks mark the gravitational mass of the two BNSM events GW170817 and GW190425 respectively. Note that the resulting baryonic mass is a prediction of our model.

Caption

The same of Fig.\ \ref{fig9} but for hyperonic matter.

Caption

The same of Fig.\ \ref{fig9} but for hyperonic matter.