Formation of black holes in the pair-instability mass gap
Abstract
In recent years, stellar models of the final phases of very massive stars have shown that pair-instability (PI) is expected to open a gap in the mass spectrum of black holes (BHs) between about 40 – 65 and 120 solar masses (Msun). This result is in tension with the detected binary BH merger GW190521 by the LIGO-Virgo collaboration, with a primary BH mass of 85 Msun and a secondary BH mass of 66 Msun.
In this talk, I present our recent work about massive star collisions, a viable formation scenario of BHs in the mass gap. Such collisions may occur in young stellar clusters. In this work, we analyzed a collision between an evolved core helium-burning star of about 58 Msun and a main-sequence star of about 42 Msun. First, we simulated the collision with a smoothed particle hydrodynamical (SPH) code. Then, we used the SPH simulation results to re-construct the post-collision star and study its evolution with detailed 1D stellar evolutionary codes. Finally, we find that the post-collision star evolves through all the stellar burning phases, avoiding PI and forming a final BH of about 87 Msun. This first study confirms that the collision scenario is a possible formation channel to populate the PI mass gap.