  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.
