Unveiling the progenitors of the most massive stellar black hole

Massive stars, with masses more than eight times that of the Sun, have long been predicted to form exotic compact objects: neutron stars and black holes. A long-standing problem has been the fate of very massive stars, more than fifty times the mass of the sun, which are expected to undergo thermonuclear explosions leading to either black hole formation or total disruption. No transient event has been detected that unambiguously matches these predicted explosions, but recent developments provide novel ways to test their existence. The detection of gravitational waves from merging black holes allows us to directly measure the masses of these remnants, while deep surveys of the variable sky can now detect thousands of supernovae every day, providing information on the birth of compact objects. I will perform a detailed theoretical study to assess the detectability of these thermonuclear explosions in ongoing surveys of the variable sky, as well as their impact on the masses and rates of merging binary black holes observable with gravitational-wave detectors. I will combine state of the art hydrodynamical simulations of these explosions, coupled with population synthesis calculations to provide a unified picture of how they can be observed both through gravitational and electromagnetic waves. This project will establish if current observations can actually test the existence of these explosive events, potentially serving as proof of their physical nature