Self-bound hybrid stars with strong phase transitions can relieve major compact star observation tensions

TL;DR

This paper proposes a new class of self-bound hybrid stars with strong phase transitions that can simultaneously explain various anomalous compact star observations, resolving existing tensions in neutron star models.

Contribution

It introduces a novel type of self-bound hybrid stars with large density discontinuities, demonstrating their ability to reconcile diverse observational data.

Findings

Self-bound hybrid stars can fit small radii and high masses of observed compact objects.

Hybrid quark, inverted hybrid, and hybrid strangeon stars serve as effective models.

The proposed stars are radially stable with strong phase transitions.

Abstract

Some recent pulsar observations cannot naturally fit into the conventional picture of neutron stars: the compact objects associated with HESS J1731-347 and XTE J1814-338 have too small radii in the low-mass regime, while the secondary component of GW190814 is too massive for neutron stars to be compatible with constraints from the GW170817 event. In this study, we demonstrate that all these anomalous observations and tensions, together with other conventional ones such as recent NICER observations of PSR J0740+6620, J0030+0451, and PSR J0437-4715, can be naturally explained simultaneously by a new general type of self-bound hybrid stars with large density discontinuities, and thus are radially stable in either the slow or rapid phase transition context. As a proof of concept, we use hybrid quark stars, inverted hybrid stars, and hybrid strangeon stars as benchmark examples to explicitly demonstrate the advantage and feasibility of self-bound hybrid stars with strong phase transitions in relieving all tensions related to compact stars' masses, radii, and tidal deformabilities.