# Massive Stellar Mergers as Precursors of Hydrogen-rich Pulsational Pair Instability Supernovae

## TL;DR

This paper explores how massive stellar mergers can lead to hydrogen-rich pulsational pair-instability supernovae, potentially explaining rare supernovae like iPTF14hls and affecting supernova rate predictions.

## Contribution

It introduces a new progenitor channel involving post-merger massive stars that can produce hydrogen-rich pulsational PISNe, expanding understanding of supernova diversity.

## Key findings

- Post-merger stars can explode as hydrogen-rich PISNe at higher rates than single-star models.
- Estimated rate of such supernovae could be a few in a thousand of all core-collapse supernovae.
- PISNe from mergers may dominate the local Universe's PISN rate.

## Abstract

Interactions between massive stars in binaries are thought to be responsible for much of the observed diversity of supernovae. As surveys probe rarer populations of events, we should expect to see supernovae arising from increasingly uncommon progenitor channels. Here we examine a scenario in which massive stars merge after they have both formed a hydrogen-exhausted core. We suggest this could produce stars which explode as pair-instability supernovae (PISNe) with significantly more hydrogen, at a given metallicity, than in single-star models with the same pre-explosion oxygen-rich core mass. We investigate the subset of those stellar mergers which later produce pulsational PISNe, and estimate that the rate of such post-merger, hydrogen-rich pulsational PISNe could approach a few in a thousand of all core-collapse supernovae. The nature and predicted rate of such hydrogen-rich pulsational PISNe are reminiscent of the very unusual supernova iPTF14hls. For plausible assumptions, PISNe from similar mergers might dominate the rate of PISNe in the local Universe.