In this work, to appear in Physical Review Letters, we analyse for the first time gravitational-wave strain data using waveforms constructed from strong gravity simulations of cosmic string loops collapsing to Schwarzschild black holes; a previously unconsidered source. Since the expected signal is dominated by a black-hole ringdown, it can mimic the observed gravitational waves from high-mass binary black hole mergers. To illustrate this, we consider GW190521, a short duration gravitational-wave event observed in the third LIGO–Virgo–KAGRA observing run. We show that describing this event as a collapsing cosmic string loop is favoured over previous cosmic string analyses by an approximate log Bayes factor of 22. The binary black hole hypothesis is still preferred, mostly because the cosmic string remnant is non-spinning. It remains an open question whether a spinning remnant could form from loops with angular momentum, but if possible, it would likely bring into contention the binary black hole preference (Work to address this question is currently ongoing as part of this DiRAC RAC15 allocation). Finally, we suggest that searches for ringdown-only waveforms would be a viable approach for identifying collapsing cosmic string events.

As part of DiRAC RAC15 Grant ACTP316: Strong gravity signatures of cosmic strings

PI: Josu Aurrekoetxea