“…Several alternative explanations for the occurrence of GW190521 have also been put forward, ranging from critically assessing uncertainties in the lower edge of the mass gap, 47,53,228,229 Population III stars at very low-metallicity, 53,54,230 accretion onto either stellar-origin 58,59,213 or primordial 231,232 BHs, and stellar mergers. 37,55,56 Additional speculations include invoking beyond-standard-model physics 233,234 exotic compact objects, 235,236 and dark-matter annihilation.…”