Speaker
Description
Massive stars are intriguing objects and key players in the cosmic cycle, yet they not totally understood, especially their fate. They, in fact, distinguish themselves from lower mass stars by the events that can take place at their death. While the majority of stars will fade away as white dwarfs, massive stars with an initial mass $\geq 8\,M_\odot$ at the end of their evolution form a degenerate iron core which collapses into a proto-neutron star (PNS). This is the starting point for a complex sequence of events with many possible outcomes. Less to moderately massive stars (with $8\lesssim M\lesssim 16\,M_\odot$) are expected to undergo an explosion during the PNS phase as core-collapse supernova (CCSN), whereas in more massive star (M $\gtrsim$16M$_\odot$) it is likely that the initial shock energy cannot disrupt the entire star, leading to a final collapse forming a black hole (BH). This event is known as ``failed supernovae''. The failed collapse could represent the end of the phenomena, unless another ingredient is added: the rotation. In case the progenitor is a massive rotating star, an accretion disk can be formed around the BH, in turn generating a disk wind. This wind has been thought as being of a sufficient energy to expel the remaining part of the star, being the source of a super energetic explosion with an energy $E_\mathrm{expl}>10^{52}$ erg and has been found to be rich in $^{56}$Ni.
In this collapsar scenario the properties of the ejecta and the $^{56}$Ni production are strongly related to the wind injection from the accretion disk and these properties had not yet been studied in a systematic manner until our latest work. Moreover these collapsar-driven explosions are associated with broad-lined Type Ic supernovae (Ic-BL SNe) and, in some cases, long gamma-ray bursts (GRBs).
Understanding the nature of these explosions requires detailed numerical modeling, capturing the formation and evolution of the central engine, the propagation of relativistic outflows, and the resulting observational signatures. In this talk, I will present our last study of the ejecta generated by the collapse of rotating massive stars, with a focus on the late-phase mass ejection after BH formation. I will do that by systematically exploring the effects of progenitor mass, rotation, and the properties of the injected wind on the dynamics of the ejecta and the production of $^{56}$Ni.This study is based on several two-dimensional hydrodynamics simulations of axisymmetric models of the ejecta generated by the collapse of rotating massive stars performed using the code \texttt{Athena++}. Based on the collapsar scenario, we assume an explosion powered through a BH-accretion disk system and investigate the impact of the disk mass and energy injected from the system on the final ejecta.
Our results focus on the distribution of the explosion energy and the injected energy of different progenitor models and on the $^{56}$Ni production computed through a particle tracing. We find a tight correlation between $E_\mathrm{expl}$ and $M_\mathrm{ej}$ and a bimodality of the explosions energy will explain in my talk. I will support our results with comparison to the observational data.
By mapping the parameter space of collapsar-driven explosions, our study sheds light on the conditions required to produce highly energetic supernovae and GRBs. We find that the diversity in explosion properties observed in broad-lined Ic SNe can be naturally explained by variations in the accretion disk characteristics and progenitor structure. Our models also suggest a possible link between long GRBs and failed SN. By extending our models to different initial conditions and varying key parameters, we aim to establish a more comprehensive understanding of the pathways leading to extreme stellar explosions. Our work provides a theoretical framework to interpret current and future observations, offering predictions that can be tested with upcoming surveys and multi-messenger facilities.
