Binary stars: It Takes Two to Tango

Authors: Lieke Van Son (Lead), Matthias Fabry, Annachiara Picco, Lucas de Sá

Overview

Most stars don’t live alone, but have a companion which whom they preform a cosmic dance throughout their lives. The interactions with their companion star, like mass transfer, tidal synchronization and common-envelope evolution, fundamentally reshape the stars’ structure, rotation, and ultimate fate. This is the cause for some of the most energetic phenomena in the universe such as X-ray binaries, stripped-envelope supernovae, and gravitational-wave mergers of black holes and neutron stars!

Today, we will learn how to use MESA/binary to trace this journey from the first interaction to the final merger. The figure below sketches the binary evolution path that stars can take towards a double black hole (BBH) merger, which provides the overarching narrative for the three labs:

Binary black hole formation channel — Schematic of binary evolution leading to a binary black hole merger. We show both the channels with (stable and unstable) mass transfer on the left, and chemically homogeneous evolution on the right.

The three labs today each zoom in on a key stage of this journey:

Lab 1 Give and Take: First mass-transfer event (RLOF): how the donor transfers mass, how the accretor receives it, and how the orbit responds.

Lab 2 Stellar Swinging: We will investigate the effects of rotation and how this can induce `chemically homogeneous evolution’ in very tight binaries. How will stellar swirling affect the final black hole spins?

Lab 3 Stable Relationships: Picking up the post-mass-transfer systems from Lab 1, we will ask how the binary continues its evolution and whether it could eventually form a double compact object (merger)?

Lab 1: Give and Take

Mass transfer: RLOF, Case A & B

Lab 2: Stellar Swinging

Rapid rotation & CHE

Lab 3: Stable Relationships

From stripped star to BBH merger