# A Semi-analytic Study of Axial Perturbations of Ultra Compact Stars

## TL;DR

This paper extends semi-analytical methods, specifically the WKB and Bohr-Sommerfeld rule, to analyze axial perturbations of ultra-compact stars and gravastars, providing new tools for understanding their stability and oscillation modes.

## Contribution

It introduces an extension of semi-analytical techniques to study perturbations of ultra-compact stars and gravastars, bridging a gap in existing methods.

## Key findings

- Extended WKB method applied to ultra-compact stars
- Estimated quasi-normal modes for gravastars
- Provided analytical insights into star stability

## Abstract

Compact object perturbations, at linear order, often lead in solving one or more coupled wave equations. The study of these equations was typically done by numerical or semi-analytical methods. The WKB method and the associated Bohr-Sommerfeld rule have been proved extremely useful tools in the study of black-hole perturbations and the estimation of the related quasi-normal modes. Here we present an extension of the aforementioned semi-analytic methods in the study of perturbations of ultra-compact stars and gravastars.