Did GW150914 produce a rotating gravastar?

TL;DR

This paper investigates whether the gravitational wave event GW150914 could have originated from a rotating gravastar instead of a black hole, concluding that current data does not support the gravastar hypothesis.

Contribution

It provides the first detailed comparison of GW150914's ringdown signal with rotating gravastar models, testing an alternative to black hole interpretation.

Findings

The ringdown signal is inconsistent with rotating gravastar models.

Current gravastar models cannot replicate the observed ringdown of GW150914.

Black hole interpretation remains the most consistent explanation.

Abstract

The interferometric LIGO detectors have recently measured the first direct gravitational-wave signal from what has been interpreted as the inspiral, merger and ringdown of a binary system of black holes. The signal-to-noise ratio of the measured signal is large enough to leave little doubt that it does refer to the inspiral of two massive and ultracompact objects, whose merger yields a rotating black hole. Yet, the quality of the data is such that some room is left for alternative interpretations that do not involve black holes, but other objects that, within classical general relativity, can be equally massive and compact, namely, gravastars. We here consider the hypothesis that the merging objects were indeed gravastars and explore whether the merged object could therefore be not a black hole but a rotating gravastar. After comparing the real and imaginary parts of the ringdown signal of GW150914 with the corresponding quantities for a variety of gravastars, and notwithstanding the very limited knowledge of the perturbative response of rotating gravastars, we conclude it is not possible to model the measured ringdown of GW150914 as due to a rotating gravastar.