Speaker
Description
Rotation has long been recognized as a potential driver of chemical mixing within the otherwise stratified radiative envelopes of massive stars. In the most extreme case, rotational mixing drives chemically homogeneous evolution (CHE), in which surface composition closely tracks core composition during the Main Sequence, forming a compact helium star by the end of hydrogen burning, and avoiding the subsequent supergiant phases. This makes CHE a potential formation channel for merging binary black holes (BBHs), as it allows for exceptionally compact orbits from zero-age Main Sequence (ZAMS). The BH yield of CHE, however, depends sensitively on assumptions about wind mass loss, internal angular momentum transport and tidal processes. The tight, <100 au, ZAMS orbits that CHE may demand also present a challenge for star formation mechanisms, and potentially lead to an ubiquitous early contact binary phase. All effects bear on the final BBH masses, spins and delay times produced by CHE stars, and their potential as progenitors of the $m_1\sim35\,\mathrm{M}_\odot$ peak in gravitational-wave (GW) BBH detections; as well as long gamma-ray bursts. Here, I introduce a set of MESA models for CHE stars geared at producing the $m_1\sim35\,\mathrm{M}_\odot$ peak, and discuss other potential signatures of rotation-driven evolution in current and future GW detections.