Accretion onto a small black hole at the center of a neutron star

Abstract

We revisit the system consisting of a neutron star that harbors a small, possibly primordial, black hole at its center, focusing on a nonspinning black hole embedded in a nonrotating neutron star. Extending earlier treatments, we provide an analytical treatment describing the rate of secular accretion of the neutron star matter onto the black hole, adopting the relativistic Bondi accretion formalism for stiff equations of state that we presented elsewhere. We use these accretion rates to sketch the evolution of the system analytically until the neutron star is completely consumed. We also perform numerical simulations in full general relativity for black holes with masses up to nine orders of magnitude smaller than the neutron star mass, including a simulation of the entire evolution through collapse for the largest black hole mass. We construct relativistic initial data for these simulations by generalizing the black hole puncture method to allow for the presence of matter, and evolve these data with a code that is optimally designed to resolve the vastly different length scales present in this problem. We compare our analytic and numerical results, and provide expressions for the lifetime of neutron stars harboring such endoparasitic black holes.

Coalescence of black hole–neutron star binaries

“…We note that, while the physical reason of the behavior at very low-mass ratios described above is not fully understood yet, it may not be unexpected taking the fact that an extremely low-mass black hole with M BH ( M NS ðQ ( 1Þ cannot make the neutron star unbound because of the tiny contribution of such a minute black hole to the dynamics of the entire system. Related simulations have been performed in the context of consumption of a neutron star by an endoparasitic black hole at the center (East and Lehner 2019;Richards et al 2021).…”

Accretion onto black holes inside neutron stars with piecewise-polytropic equations of state: analytic and numerical treatments

“…In particular, there exists a minimum steadystate accretion rate for stiff EOSs. As shown in Appendix A of [21], these results also hold for a black hole inside a neutron star, as long as the black hole mass M BH is much smaller than that of the neutron star, M BH M NS . In this case the relativistic Bondi formalism yields the accretion rate as measured by a "local asymptotic observer", i.e.…”

Gravitational-wave Emission from a Primordial Black Hole Inspiraling inside a Compact Star: a Novel Probe for Dense Matter Equation of State

“…where λ is the accretion eigenvalue depending on the EoS of the accreted matter. Equation 6 is applicable for m PBH M CS (Richards et al 2021), where M CS is the mass of the compact star.…”

“…For the parameter λ, although there are analytical expressions for EoSs when the adiabatic index is Γ 1 (Richards et al 2021;Aguayo-Ortiz et al 2021), no simple expression is available when Γ < 1 (at the phase transition region of a NS; Potekhin et al 2013) and Γ → ∞ (at the surface of a SS; Xia et al 2021). So, we use a commonly-used value of Γ = 4/3 in our calculations, which naturally gives λ = 1/ √ 2 (Génolini…”