Recovery from Giant Eruptions in Very Massive Stars

TL;DR

This study models the post-eruption evolution of very massive stars using energy-conserving simulations, revealing sustained winds driven by pulsations and significant mass loss over centuries.

Contribution

It introduces a novel energy-conserving simulation approach to study the aftermath of giant eruptions in very massive stars, focusing on their long-term behavior.

Findings

Stars develop ~400 km/s winds with decreasing mass loss rates.

Post-eruption outflows can carry more mass than the initial eruption.

Simulations show sustained mass loss over ~200 years driven by pulsations.

Abstract

We use a hydro-and-radiative-transfer code to explore the behavior of a very massive star (VMS) after a giant eruption -- i.e., following a supernova impostor event. Beginning with reasonable models for evolved VMSs with masses of $80~M_\odot$ and $120~M_\odot$, we simulate the change of state caused by a giant eruption via two methods that explicitly conserve total energy: 1. Synthetically removing outer layers of mass of a few $M_\odot$ while reducing the energy of the inner layers. 2. Synthetically transferring energy from the core to the outer layers, an operation that automatically causes mass ejection. Our focus is on the aftermath, not the poorly-understood eruption itself. Then, using a radiation-hydrodynamic code in 1D with realistic opacities and convection, the interior disequilibrium state is followed for about 200 years. Typically the star develops a $\sim 400 ~\rm{km}~\rm{s}^{-1}$ wind with a mass loss rate that begins around $0.1 ~M_\odot~\rm{yr^{-1}}$ and gradually decreases. This outflow is driven by $\kappa$-mechanism radial pulsations. The 1D models have regular pulsations but 3D models will probably be more chaotic. In some cases a plateau in the mass-loss rate may persist about 200 years, while other cases are more like $\eta$ Car which lost $>10~M_\odot$ and then had an abnormal mass loss rate for more than a century after its eruption. In our model, the post-eruption outflow carried more mass than the initial eruption. These simulations constitute a useful preliminary reconnaissance for 3D models which will be far more difficult.