Unified models of long gamma-ray bursts: from stellar progenitors and BLACK holes to Jets and Electromagnetic Transients

Long gamma-ray bursts (LGRBs) are the most violent explosions in the Universe after the Big Bang, occurring during the collapse of a massive star that leaves behind a newly formed compact object and launches powerful relativistic jets.At more than 55 years from their discovery, the mechanism responsible for the electromagnetic emission of LGRBs remains unclear, just as the nature of the accreting compact object that powers them up.The huge scale separation between different processes (the gravitational collapse and the onset of the supernova, the propagation of the jet through the star, and the production of high-energy emission from the jet at large distances) usually forces theoretical and numerical models to focus on a specific stage of the LGRB, rather than considering them all at once.To this day, there are two fundamental questions that remain unanswered:- What is the main prompt emission mechanism? Several models are currently proposed, which are in some cases mutually exclusive and are highly dependent on the properties of the jet and the central engine's dynamics.- What is the central engine of a LGRB? To date there are two competing scenarios, involving either an accreting black hole (collapsar) or a highly magnetized proto-neutron star (millisecond magnetar). Combining state-of-the-art core-collapse supernova models with high-performance GPU-accelerated relativistic jet simulations, the BlackJET project will provide a unified picture of LGRBs by consistently modeling all stages from the start of the stellar collapse to the observed electromagnetic emission.This holistic approach will unveil the intimate connection between stellar progenitor, accreting central engine, and relativistic jet, ultimately disclosing the observational signatures that a realistic LGRB progenitor should produce.By bridging the gap between stellar evolution and GRB astronomy we will be able to effectively address the fundamental questions about the nature of LGRBs.