Dark Matter Heating in Evolving Proto-Neutron Stars: A Two-Fluid Approach

TL;DR

This work analyzes how asymmetric dark matter (DM), modeled as either a fermionic core or a self-interacting bosonic core/halo, impacts the thermal and structural evolution of proto-neutron stars under a gravity-only two-fluid framework. By combining a relativistic mean-field OM equation of state (DDME2) at finite temperature with two DM models (fermionic mirror DM and bosonic DM with Bose–Einstein condensation) and solving the two-fluid TOV equations, it demonstrates a gravitational heating mechanism from DM cores and a halo-driven cooling effect from extended DM distributions. The key finding is that DM cores deepen the central potential and heat the baryonic matter, while DM halos provide external support that can cool the core, with hyperons further softening the EoS and shifting hyperon onset. These distinct, stage-dependent signatures offer observational diagnostics in supernova neutrino light curves and the early cooling of young pulsars, enabling potential discrimination of DM presence and its spatial distribution in NSs, independent of non-gravitational DM–OM couplings.

Abstract

Neutron stars (NSs) provide a unique laboratory to probe dark matter (DM) through its gravitational imprint on stellar evolution. We use a two-fluid framework with non-annihilating, asymmetric DM, both fermionic and bosonic, that interacts with ordinary matter (OM) solely through gravity. Within this framework, we track proto-neutron stars (PNSs) across their thermal and compositional evolution via quasi-static modeling over the Kelvin--Helmholtz cooling timescale. We uncover a distinct thermal signature: DM cores deepen the gravitational potential, compressing and heating the baryonic matter, while extended DM halos provide external support, leading to cooling of the stellar matter. In contrast, hyperons and other exotic baryons soften the equation of state similarly to DM cores but reduce, rather than increase, the temperature. DM thus alters both temperature and particle distribution profiles in ways that provide a clear diagnostic of its presence. DM cores also enhance compactness and shift hyperon onset, with the strongest effects during deleptonization and neutrino-transparent phases due to reduced neutrino pressure contributions. Consequently, this early thermal evolution, observable through supernova neutrino light curves and young pulsar cooling curves, offers a direct, testable probe of DM in NSs.

Figures (6)

• Figure 1: Variation of the core pressure of a $1.55\,\rm M_\odot$ star as a function of normalized radius ($r/R$) for the evolution of PNSs admixed with bosonic DM. The left and middle panels represent stars with a fixed DM fraction in the core, while the right panel represents stars with a DM halo for various stages of stellar evolution. The color codes represent different thermodynamic stages, while the line styles indicate the DM fractions.
• Figure 2: Particle distribution profiles versus normalized radius for a PNS with $M_B = 1.55\,M_\odot$, comparing a purely hyperonic EoS with three DM core configurations (1%, 5%, and 10%). Top panels: neutrino-trapped regime—left: first stage ($s_B = 1,\, Y_l = 0.4$), right: second stage ($s_B = 2,, Y_l = 0.2$). Bottom panels: neutrino-transparent regime; left: third stage ($s_B = 2,\, Y_{\nu_e} = 0$), right: final cold, catalyzed NS ($T = 0$ MeV).
• Figure 3: Mass–radius relations for PNS models with and without DM. The first panel shows hot PNSs configurations, including neutrino-trapped cases with varying $s_B$ and $Y_l$, compared with a neutrino-transparent case ($s_B=2$, $Y_{\nu_e}=0$). Curves are color-coded by composition and styled by DM fraction: no-DM (solid), 1% (dashed), 5% (dash-dotted), and 10% (dotted). The middle panel presents cold ($T=0$ MeV) NS configurations, comparing nucleonic (black) and hyperonic (blue) stars, with line styles indicating $F_D$. Observational constraints include GW170817 (steel blue, 90% and 50% CIs) LIGOScientific:2018hze, NICER posteriors for PSR J0030+0451 (cyan/yellow) Riley:2019ydaMiller:2019cac, PSR J0740+6620 (violet) Riley:2021pdlMiller:2021qha, and PSR J0437–4715 (lilac) Choudhury:2024xbk, as well as HESS J1731–347 (red, 90% and 50% CL) 2022NatAs...6.1444D. The last panel shows the DM-halo configuration with $F_D=1\%, 5\%$, and 10%, where colors denote thermodynamic stages: $s_B=1,\ Y_l=0.4$ (red), $s_B=2,\ Y_l=0.2$ (blue), $s_B=2,\ Y_{\nu_e}=0$ (green), and $T=0$ MeV (black).
• Figure 4: Temperature profiles as a function of normalized radius $r/R$ for PNSs with bosonic and fermionic DM cores. The first panel shows nucleonic stars with bosonic DM, the middle panel hyperonic stars with bosonic DM, and the last panel nucleonic stars with fermionic DM. Colors represent thermal and lepton fraction conditions: $s_B = 1,\ Y_l = 0.4$ (red), $s_B = 2,\ Y_l = 0.2$ (blue), and $s_B = 2,\ Y_{\nu_e} = 0.0$ (green). Line styles indicate DM fractions: 1% (dash-dotted), 5% (dashed), and 10% (dotted).
• Figure 5: Radial temperature profiles for dark matter halo configurations of NSs with varying dark matter fractions (No DM, 1%, 5%, and 10%). Each color represents a different thermal and lepton configuration: $s_B=1,\,Y_l=0.4$ (red), $s_B=2,\,Y_l=0.2$ (blue), and $s_B=2,\,Y_{\nu_e}=0.0$ (green). The temperature is plotted as a function of normalized radius. The inset zooms into the region $r/R \in [0.4,\,0.6]$ for the case $s_B=1,\ Y_l=0.4$.