Hyperons and $Δ$'s in rotating protoneutron stars: Local properties

TL;DR

This study models rotating protoneutron stars with hyperons and Delta resonances using a density-dependent relativistic mean-field EoS to connect local thermodynamic and compositional properties with global evolution under neutrino-driven angular-momentum changes. By tracking four evolutionary snapshots and three composition tracks (N, NH, NHD), it shows that deformation and thermal evolution are governed by angular momentum, mass, and composition, with rapid rotation and exotic degrees of freedom enhancing deformation and lowering core temperature. In the realistic PSR J0740+6620 scenario, deformation remains modest while NICER constraints on equatorial radius are satisfied, illustrating stringent EoS requirements when rotation, mass, and composition are jointly considered. The results underscore the necessity of self-consistent rotation-treatment and composition-dependent modeling to accurately describe protoneutron star evolution in the era of multi-messenger astrophysics and NICER-era constraints.

Abstract

The structural evolution of rotating protoneutron stars encodes essential information about their observable signatures, while microscopic properties provide complementary knowledge to advance observational investigations. Using a relativistic mean-field model with density-dependent couplings that account for temperature and particle composition, we investigate rotation, neutrino-emission-driven changes in angular momentum, particle distributions, temperature profiles, and sound speed to probe the internal dynamics of protoneutron star matter. Additionally, we track the evolution of macroscopic quantities such as energy distribution and gravitational mass and establish direct links between microphysics and global evolution. Extending the framework of Phys. Rev. D 112, 023007 (2025), which focuses on the global properties of rotating protoneutron star evolution, our results reveal that protoneutron star deformation and thermal evolution are governed by angular momentum, mass, and composition. Exotic matter (hyperons and $Δ$-resonances) and rapid rotation enhance deformation leading to a reduction in core temperature, whereas slowly rotating stars like PSR J0740$+$6620 remain nearly spherical. Our predicted equatorial radii for PSR J0740$+$6620, $13.0\ \mathrm{km} < R_e < 13.5\ \mathrm{km}$, are consistent with NICER measurements. These findings constrain the EoS, requiring a self-consistent treatment of rotation, mass-dependent compression, and composition-driven modeling to accurately model protoneutron star evolution in the context of multi-messenger astrophysics.

Figures (12)

• Figure 1: Profiles of temperature versus normalized equatorial plane radius, $r/R_e$, for a star with $M_0 = 1.60$$M_\odot$, solid lines are for conserved angular momentum, dashed lines are for loss of angular momentum by neutrino emission, and dash-double-dot lines are for static stars. Top left: $s_B=1$ and $Y_L=0.4$, top right: $s_B=2$ and $Y_L=0.2$, bottom: $s_B=2$ and $Y_{\nu_e}=0$.
• Figure 2: Profiles of squared sound velocity versus the equatorial plane radius, $r$, for a star with $M_0 = 1.60$$M_\odot$, solid lines are for conserved angular momentum, dashed lines are for loss of angular momentum by neutrino emission, and dash-double-dot lines are for static stars.
• Figure 3: Profiles of particle distribution versus the equatorial plane radius for a star with $M_0 = 1.60$$M_\odot$ and considering the EoS with nucleons plus hyperons and delta resonances (NHD). Solid lines are for conserved angular momentum, dashed lines are for loss of angular momentum by neutrino emission, and dash-double-dot lines are for static stars. Vertical lines represent the radius where the stellar crust begins.
• Figure 4: Contour plots of a PNS with a baryonic mass of $M_0 = 1.60$$M_\odot$, composed of nucleons, hyperons and delta resonances (NHD EoS), during the neutrino opaque stages of evolution. The evolutionary stage of each panel is indicated at the top, while the legend for the meaning of each color is shown on the right. The left panels show the rapidly rotating scenario with conserved angular momentum, while the right panels represent the static scenario. From the surface toward the center of the star, each layer corresponds to the radial position where a specific type of particle begins to appear in the stellar matter. "N+L" denotes nucleons plus leptons. The values indicated along each contour represent the baryon density $(n_B/n_0)$, at that location.
• Figure 5: Contour plots of a PNS with a baryonic mass of $M_0 = 1.60$$M_\odot$, composed of nucleons, hyperons and delta resonances (NHD EoS), during the neutrino transparent stages of evolution. The evolutionary stage of each panel is indicated at the top, while the legend for the meaning of each color is shown on the right. The left panels show the rapidly rotating scenario with conserved angular momentum, while the right panels represent the static scenario. From the surface toward the center of the star, each layer corresponds to the radial position where a specific type of particle begins to appear in the stellar matter. "N+L" denotes nucleons plus leptons. The values indicated along each contour represent the baryon density $(n_B/n_0)$, at that location.