A model-agnostic analysis of hybrid stars with reactive interfaces

TL;DR

This paper investigates how the speed of hadron-quark conversion at the interface affects the stability and structure of hybrid stars, demonstrating the existence of a new class of stable hybrid objects compatible with current observational constraints.

Contribution

It introduces a model-agnostic approach to analyze hybrid stars considering the conversion speed, revealing a new stable class of hybrid stars with high central densities.

Findings

Slow conversion speeds allow for stable hybrid stars with very stiff equations of state.

Current observational constraints can be satisfied in scenarios with different transition pressures.

A new class of hybrid stars with dense cores is theoretically possible.

Abstract

We study hybrid stars considering the effects on stellar stability of the hadron-quark conversion speed at the sharp interface. The equation of state is constructed by combining a model-agnostic hadronic description with a constant speed of sound model for quark matter. We show that current LIGO/Virgo, NICER, low-density nuclear and high-density perturbative QCD constraints can be satisfied in two scenarios, with low and high transition pressures. If the conversion speed at the interface is slow, a new class of dynamically stable hybrid objects is possible and very stiff hadronic equations of state cannot be discarded. Densities tens of times larger than the nuclear saturation density are possible at the center of these objects. We discuss possible formation mechanisms for the new class of hybrid stars and smoking guns for their observational identification.