Triggering Electron Capture Supernovae: Dark Matter Effects in Degenerate White-Dwarf-like Cores of Super-Asymptotic Giant Branch Stars

TL;DR

This paper explores how fermionic asymmetric dark matter influences the evolution of white dwarf cores, potentially triggering electron-capture supernovae at lower masses and resulting in dark matter-admixed neutron stars with distinct properties.

Contribution

It introduces a relativistic two-fluid model for ordinary matter and dark matter, revealing their impact on supernova thresholds and remnant characteristics, a novel approach in ECSN studies.

Findings

Dark matter increases core density, lowering ECSN threshold mass.

Remnants are stable dark matter-admixed neutron stars with lower masses.

Conversion energy during collapse decreases with higher dark matter mass and fraction.

Abstract

Electron-capture supernovae (ECSNe) have emerged as a compelling formation channel for low-mass neutron stars, bolstered by decades of theoretical work and increasingly supported by observational evidence, including the recent identification of SN~2018zd. Motivated by this, we investigate the influence of fermionic asymmetric dark matter (ADM) on the equilibrium structure of progenitor cores and the formation of their neutron star remnants. Using a general relativistic two-fluid formalism, we model the coupled evolution of ordinary matter (OM) and ADM, treated as separately conserved fluids interacting solely through gravity. Our analysis focuses on neon-rich white dwarfs (Ne WDs), which are typical progenitor cores for ECSNe. We assume conservation of both baryon number ($N_B$) and dark matter particle number ($N_D$) during collapse, allowing for a consistent mapping between progenitor and remnant configurations. We find that ADM significantly enhances the central density of the WD progenitor. This lowers the threshold gravitational mass $M^*$ required to initiate electron capture, enabling ECSNe from lower-mass progenitors. The resulting remnants are stable, dark matter-admixed neutron stars with gravitational masses potentially well below current observational bounds. Moreover, we find that the conversion energy during the WD-to-NS conversion is also significantly reduced for higher ADM particle masses and fractions, suggesting that unusually low-energy ECSNe may serve as potential indicators of ADM involvement in stellar collapse.