Three-dimensional general relativistic MHD simulations of jet formation and propagation in self-gravitating collapsing stars

Context. Discovered almost sixty years ago, gamma-ray bursts are the most powerful explosions in the Universe. Long gamma-ray bursts are associated with the collapse of rapidly rotating massive stars, which conclude their lives as stellar-mass black holes. During this process, the initial mass of the black hole is several times smaller than the remaining mass of the progenitor. Taking into account self-gravity of the star may significantly modify the process of jet formation. This potentially affects the prompt emission. Aims. We investigate collapsar models with and without self-gravity under identical initial conditions to directly compare the effects of self-gravity on jet properties, such as the opening angle, jet power, and the terminal Lorentz factor, including its variability. Methods. We computed a suite of time-dependent, three-dimensional general relativistic magnetohydrodynamic (GRMHD) simulations of collapsars in evolving spacetime. We updated the Kerr metric components due to the growth of the black hole mass and changes in its angular momentum. The self-gravity was considered via perturbative terms. Results. We present for the first time the process of jet formation in self-gravitating collapsars. We find that self-gravity leads to temporary jet quenching, which can explain some features in the gamma-ray burst prompt emission. We find no substantial difference in jet launching times between models with and without self-gravity. We observe that in the absence of self-gravity, the jet can extract more rotational energy from the black hole, while self-gravitating models produce narrower jet opening angles. We show that under certain conditions, self-gravity can interrupt the jet formation process, resulting in a failed burst. Conclusions. Our computations show that self-gravity significantly modifies the process of jet propagation, resulting in notably different jet properties. We show that the timescales, variability, and opening angle of jet depend on whether self-gravity is included or not. We argue that self-gravity can potentially explain certain prompt emission properties due to the jet quenching.