Envelope Inflation and outflow Driven by Energy Deposition in Massive Stars

TL;DR

This study uses hydrodynamical simulations to show how energy deposition inside massive stars causes envelope expansion and outflows, potentially leading to mass ejections and stellar envelope unbinding.

Contribution

It demonstrates that impulsive energy input in massive stars can drive strong outflows and envelope expansion, providing insight into mass ejection mechanisms.

Findings

Energy deposition causes significant envelope expansion.

High energy input can unbind outer stellar material.

Outflows are triggered by impulsive energy release.

Abstract

Evolved massive stars are known to undergo outflow with high mass ejections, resulting in the loss of a substantial portion of their envelopes. One proposed mechanism driving these events is the release or deposition of energy within the stellar envelope. We use a one-dimensional hydrodynamical code to investigate the resulting outflow and stellar response to energy deposition at specific regions inside a $\rm 70 \, M_{\odot}$ star. We compare hydrostatic and hydrodynamic models and test for different energies and widths of the depositing region. We find that due to the deposited energy, the envelope expands significantly, and under certain conditions, such as assuming a uniform electron scattering opacity, this energy input becomes sufficient to unbind material from the outer envelope. This, in turn, leads to the formation of an outflow. We find that higher deposited energy triggers a strong outflow and results in a somewhat hotter and less expanded envelope due to the rapid loss of energy through expelled material. This driving mechanism leads to sudden envelope expansion and the formation of strong outflows in our models, highlighting the generic hydrodynamic response of massive star envelopes to impulsive energy input.