In a paper published in Phys. Rev. Lett, Gr@v member Nico Sanchis-Gual and co-authors reports a degeneracy between the gravitational-wave signals emitted in quasi-circular precessing black-hole mergers and those from extremely eccentric mergers, namely head-on collisions.
This results shows that head-on mergers could be identified as precessing quasi-circular intermediate-mass black hole binaries, located at a much larger distance and with component masses inside (outside) the pair-instability supernova gap, while the true scenario has masses outside (inside) this gap. The paper also discusses the implications for GW190521 and similar events.