# Stable Schwarzschild stars as black-hole mimickers

## TL;DR

The paper demonstrates that Schwarzschild stars, ultracompact objects with positive pressure, can mimic black holes closely in their quasinormal modes and are stable against nonspherical perturbations, making them potential black-hole mimickers.

## Contribution

It extends stability analysis of Schwarzschild stars to nonspherical perturbations and shows their quasinormal modes can closely resemble those of black holes, highlighting their mimicking potential.

## Key findings

- Schwarzschild stars are stable against nonspherical perturbations.
- Their quasinormal modes can be arbitrarily close to black holes.
- No echoes are observed at the end of ringdown, with late-time tails dominating.

## Abstract

The Schwarzschild star is an ultracompact object beyond the Buchdahl limit, which has Schwarzschild geometry outside its surface and positive pressure in the external layer which vanishes at the surface. Recently it has been shown that the Schwarzschild star is stable against spherically symmetric perturbations. Here we study arbitrary axial nonspherical perturbations, and show that the observable quasinormal modes can be as close to the Schwarzschild limit as one wishes, what makes the Schwarzschild star a very good mimicker of a black hole. The decaying time-domain profiles prove that the Schwarzschild star is stable against nonspherical perturbations as well. Another peculiar feature is the absence of echoes at the end of the ringdown. Instead we observe a nonoscillating mode which might belong to the class of algebraically special modes. At asymptotically late times, Schwarzschildian power-law tails dominate in the signal.