Giant Eruptions in Massive Stars and their Effect on the Stellar Structure

TL;DR

This study models giant eruptions in massive stars using stellar evolution simulations, revealing how these events cause significant structural changes and temporary luminosity drops, with potential for cyclic eruptions.

Contribution

It introduces a detailed simulation of giant eruptions in a 70 solar mass star, showing the star's structural response and recovery, a novel approach to understanding LBV eruptions.

Findings

Star contracts and releases gravitational energy during eruption.

Luminosity drops by about one order of magnitude.

Star recovers to near initial state after ~87 years.

Abstract

Giant eruptions (GE) in Luminous blue variables (LBVs) are years to decades-long episodes of enhanced mass loss from the outer layers of the star during which the star undergoes major changes in its physical and observed properties. We use the \textsc{mesa} stellar evolution code to model the evolution of a $70~M_{\odot}$ star that undergoes a GE. We let the star evolve to the termination of the main sequence (MS) and when it reaches $T\simeq 19\,400 $ K we emulate a GE by removing mass from its outer layers, at a rate of $0.15~ M_{\odot}~\rm yr^{-1}$ for 20 years. As mass is being lost, the star contracts and releases a substantial amount of gravitational energy. The star undergoes an initial $\simeq 3$ days of expansion followed by years of contraction. During that time the star tries to reach an equilibrium state and as a result of loss in gravitational energy, its luminosity drops about one order of magnitude. As the GE terminates, we let the star continue to evolve without any further mass loss and track its recovery as it regains its equilibrium by adjusting its internal structure. After $\simeq 87$ years it reaches a state very close to the one where the GE was first initiated. We suggest that at this point another GE or a cycle of GEs may occur.