The impact of stellar rotation on the black hole mass-gap from pair-instability supernovae

Abstract

Models of pair-instability supernovae (PISNe) predict a gap in black hole (BH) masses between ∼45 M⊙ and 120 M⊙, which is referred to as the upper BH mass-gap. With the advent of gravitational-wave astrophysics, it has become possible to test this prediction, and there is an important associated effort to understand which theoretical uncertainties modify the boundaries of this gap. In this work we study the impact of rotation on the hydrodynamics of PISNe, which leave no compact remnant, as well as the evolution of pulsational-PISNe (PPISNe), which undergo thermonuclear eruptions before forming a compact object. We perform simulations of nonrotating and rapidly rotating stripped helium stars in a metal-poor environment (Z⊙/50) in order to resolve the lower edge of the upper mass-gap. We find that the outcome of our simulations is dependent on the efficiency of angular momentum transport: models that include efficient coupling through the Spruit-Tayler dynamo shift the lower edge of the mass-gap upward by ∼4%, while simulations that do not include this effect shift it upward by ∼15%. From this, we expect that the lower edge of the upper mass-gap is dependent on BH spin, which can be tested as the number of observed BH mergers increases. Moreover, we show that stars undergoing PPISNe have extended envelopes (R ∼ 10 − 1000 R⊙) at iron-core collapse, making them promising progenitors for ultra-long gamma-ray bursts.

Chemically homogeneous evolution: a rapid population synthesis approach

“…In particular, the WR star formed when the CH star contracts and spins up at the end of its MS is likely to be critically rotating, and the same process may repeat during core contraction after core helium depletion. The star's angular momentum can be reduced to sub-critical levels with a small amount of mass loss, and therefore does not significantly impact the overall mass budget; however, this does affect the remnant spin Marchant & Moriya (2020).…”

Fast Blue Optical Transients Due to Circumstellar Interaction and the Mysterious Supernova SN 2018gep

“…If it can produce pre-SN ejecta of ∼0.3 M e due to pulsational pair instability before collapse and generate a ∼10 52 erg explosion with a few solar masses of high-velocity ejecta, it could likely produce an event like SN 2018gep. Recent work (Marchant & Moriya 2020) shows that whether pulsation occurs depends on how fast the star is rotating. Their rigidly rotating models show pulsations, which release less than half of the stellar angular momentum.…”

Find the Gap: Black Hole Population Analysis with an Astrophysically Motivated Mass Function

“…where: M * is a stellar mass and  q are nuisance parameters such as metallicity, redshift, binarity, or rotation (Farmer et al 2019;Marchant et al 2019;Marchant & Moriya 2020;Woosley & Heger 2021); and ( )…”