Rotational Properties of Inverted Hybrid Stars

TL;DR

This paper explores the rotational behavior of inverted hybrid stars with quark and hadron layers, revealing unique phenomena like increased twin configurations and back-bending effects due to their inverted structure and phase transitions.

Contribution

It introduces the study of rotation in inverted hybrid stars, highlighting their distinct properties and potential for mini-collapses, which were not previously analyzed in detail.

Findings

Higher mass and larger radius at Kepler frequencies for cross stars

Increased potential for twin star configurations during rapid rotation

Occurrence of mini-collapses during spin-down sequences

Abstract

We study the rotational properties of inverted hybrid stars (also termed cross stars), which have been recently proposed as a possible new class of compact stars characterized by an outer layer of quark matter and a core of hadrons, in an inverted structure compared to traditional hybrid stars. We analyze distinct models representing varying depths of quark-hadron phase transitions. Our findings reveal that, while cross stars rotating at their Kepler frequencies typically exhibit a significantly higher mass and larger circumferential radius as anticipated, interestingly, there is a significant increase in potential twin configurations in the case of rapid rotations. We further study sequences of constant baryonic mass, representing potential paths of rotational evolution. Our results indicate that not all stars in these sequences are viable due to the onset of phase transitions during spin-down, leading to possible mini-collapses. We also investigate the phenomenon of ``back-bending" during spin-down sequences, which is manifested in a rather different shape for cross stars due to their inverted structure and the large density discontinuity caused by the strong phase transition, in contrast to traditional hybrid stars. Our research enriches existing studies by introducing the significant aspect of rotation, unveiling intr