Stellar Evolution in Close Binaries: Processes and Outcomes

TL;DR

This paper reviews stellar evolution in close binary systems, focusing on mass transfer processes, the formation of binary pulsars, black hole interactions, and the origin of Blue Straggler Stars, highlighting current modeling challenges.

Contribution

It provides a comprehensive analysis of binary evolution processes, including irradiation feedback, evaporation, and the formation of Blue Stragglers, addressing gaps in existing models.

Findings

Standard models fail to explain binary pulsars with long mass transfer episodes.

Black holes in binaries are unlikely to be spun up after formation if born non-rotating.

Mass transfer in close binaries is a plausible channel for Blue Straggler Star formation.

Abstract

We discuss some aspects of stellar evolution in binary systems. While single stars can swell following the chemical evolution of their interior, stars belonging to binary systems cannot overflow the size of the Roche lobe and hydrostatic equilibrium is strictly impossible. The system is forced to exchange mass between its members through the inner Lagrangian point. In the first part of the paper, we discuss the standard evolution of binaries that have a non-degenerate donor star and a compact companion. We show that the model fails when to account for the occurrence of binary pulsars when they predict a long-standing mass transfer episode. Models including irradiation feedback and evaporation in close binaries are examined next. Following these sections, we discuss the case of systems with a black hole (BH). We show that if BHs are born non-rotating, binary interaction seems insufficient to speed them up, an indication that BH rotation is a feature present at birth. Finally, we discuss Blue Straggler Stars detected in open and globular clusters. Since they cannot be understood as single-born stars, we evaluate one of the proposed channels is mass transfer in close binaries, and discuss its viability and the limitations of the present models.