Simulating the outcome of binary neutron star merger in common envelope jets supernovae

TL;DR

This study uses 3D hydrodynamical simulations to explore how neutron star mergers inside red supergiant stars influence the envelope and potentially produce luminous transient events called CEJSNe.

Contribution

It introduces a detailed simulation of neutron star mergers within RSG envelopes and examines their impact on the energy and dynamics of CEJSNe.

Findings

Over 90% of the inner RSG envelope remains bound after merger energy deposition.

Merger-induced jets can power luminous transient events (CEJSNe).

The merger process can lead to more energetic CEJSNe through continued in-spiral and accretion.

Abstract

We simulate the influence of the energy that the merger process of two neutron stars (NSs) releases inside a red supergiant (RSG) star on the RSG envelope inner to the merger location. In the triple star common envelope evolution (CEE) that we consider a tight binary system of two NSs spirals-in inside an RSG envelope and because of mass accretion and dynamical friction the two NS merge. We deposit merger-explosion energies of 3e50 and 1e51 erg at distances of 25Ro and 50Ro from the center of the RSG, and with the three-dimensional hydrodynamical code FLASH we follow the evolution of the RSG envelope in inner regions. For the parameters we explore we find that more than 90 per cent of the RSG envelope mass inner to the merger site stays bound to the RSG. NSs that experience a CEE are likely to accrete RSG envelope mass through an accretion disk that launches jets. These jets power a luminous transient event, a common envelope jets supernova (CEJSN). The merger process adds to the CEJSN energy. Our finding implies that the interaction of the merger product, a massive NS or a BH, with the envelope can continue to release more energy, both by further in-spiral and by mass accretion by the merger product. Massive RSG envelopes can force the merger product to spiral-in into the core of the RSG, leading to an even more energetic CEJSN.