On the response of massive main sequence stars to mass accretion and outflow at high rates

TL;DR

This study uses a one-dimensional stellar evolution model to show that massive main-sequence stars can accrete at high rates without significant expansion if they simultaneously lose a substantial portion of the accreted mass via jets, which helps maintain a deep gravitational potential.

Contribution

It introduces a model where jet-driven mass loss during accretion prevents excessive stellar expansion, providing new insights into the behavior of massive stars in high accretion scenarios.

Findings

Massive stars can accrete rapidly without expanding if they lose half or more of the accreted mass via jets.

Jet activity maintains a deep gravitational potential, enabling high-energy jet launching.

Results are relevant to understanding bright transient events like luminous red novae and Eta Carinae's Great Eruption.

Abstract

With a one-dimensional stellar evolution model, we find that massive main-sequence stars can accrete mass at very high mass accretion rates without expanding much if they lose a significant fraction of this mass from their outer layers simultaneously with mass accretion. We assume the accretion process is via an accretion disk that launches powerful jets from its inner zones. These jets remove the outer high-entropy layers of the mass-accreting star. This process operates in a negative feedback cycle, as the jets remove more envelope mass when the star expands. With the one-dimensional model, we mimic the mass removal by jets by alternative mass addition and mass removal phases. For the simulated models of 30Mo and 60Mo, the star does not expand much if we remove more than about half of the added mass in not-too-short episodes. This holds even if we deposit the energy the jets do not carry into the envelope. As the star does not expand much, its gravitational potential well stays deep, and the jets are energetic. These results are relevant to bright transient events of binary systems powered by accretion and the launching of jets, e.g., intermediate luminosity optical transients, including some luminous red novae, the grazing envelope evolution, and the 1837-1856 Great Eruption of Eta Carinae.