[Paper Review] Physics of Binary Star Evolution -- from Stars to X-ray Binaries and Gravitational Wave Sources

Thomas M. Tauris, E. P. J. van den Heuvel|arXiv (Cornell University)|May 16, 2023

Pulsars and Gravitational Waves Research17 references45 citations

TL;DR

A comprehensive textbook that traces binary star evolution from basic physics to the formation of X-ray binaries and gravitational-wave sources, linking theory with observations and future surveys.

ABSTRACT

The majority of all stars are members of a binary system. The evolution of such binary stars and their subsequent production of pairs of compact objects in tight orbits, such as double neutron stars and double black holes, play a central role in modern astrophysics, Binary evolution leads to the formation of different types of violent cosmic events such as novae, supernova explosions, gamma-ray bursts, mass transfer and accretion processes in X-ray binaries, and the formation of exotic radio millisecond pulsars. In some cases, the binary systems terminate as spectacular collisions between neutron stars and/or black holes. These collisions lead to powerful emission of gravitational waves, as detected by LIGO since 2015. The coming decade is expected to reveal a large number of discoveries of binary compact systems, as well as their progenitors and merger remnants, from major instruments such as the radio Square-Kilometre Array; the gravitational wave observatories LIGO-Virgo-KAGRA-IndIGO and LISA; the astrometric space observatory Gaia; the James Webb Space Telescope; and the X-ray space observatories eXTP, STROBE-X, and Athena. In this light, it is important to have a modern textbook on the physics of binary stars evolution, from ordinary stars to X-ray binaries and gravitational wave sources. The scope of this book is that the reader (student or educated expert) will learn the physics of binary interactions, from stellar birth to compact objects, and relate this knowledge to the latest observations. The reader will learn about stellar structure and evolution, and detailed binary interactions covering a broad range of phenomena, including mass transfer and orbital evolution, formation and accretion onto compact objects (white dwarfs, neutron stars and black holes), and their observational properties. Exercises are provided throughout the book.

Motivation & Objective

• Explain why binary star evolution is central to many astrophysical phenomena (X-ray sources, supernovae, pulsars, gravitational waves).
• Develop the physical framework for binary interactions including mass transfer, Roche lobes, common envelopes, and orbital evolution.
• Connect theoretical models to observed binaries (non-degenerate, white dwarf, X-ray binaries) and to the formation of compact objects (NSs, BHs).
• Present pathways from massive binaries to double compact objects and their mergers, including implications for gravitational-wave astronomy.
• Introduce binary population synthesis and statistical methods to connect theory with the observed binary population.

Proposed method

• Provide historical context and physical foundations for binary evolution.
• Derive and discuss Roche equipotentials, mass transfer stability, and orbital changes due to transfer and loss.
• Categorize observed binaries and detail the physics of accretion, disks, winds, and tidal evolution.
• Analyze evolutionary channels from single stars to binaries with NS/BH remnants and the role of common envelopes.
• Describe observational diagnostics for X-ray binaries and pulsars and how they constrain theory.
• Outline population synthesis approaches and compare empirical vs. theoretical merger rate estimates.

Experimental results

Research questions

• RQ1 What are the key physical processes that drive binary interactions (mass transfer, angular momentum loss) and how do they shape binary evolution?
• RQ2 What are the formation channels for X-ray binaries, double neutron stars, and double black holes, and how do kicks and mass transfer influence outcomes?
• RQ3 How do observations of X-ray binaries, pulsars, and supernovae inform models of binary evolution?
• RQ4 What are the methods and limitations of binary population synthesis in predicting merger rates and distributions?
• RQ5 How will upcoming facilities (e.g., SKA, LISA, Athena) advance our understanding of binary evolution and gravitational-wave sources?

Key findings

• Binary evolution is essential to a wide range of astrophysical phenomena, including X-ray binaries, supernovae, and gravitational-wave sources.
• Binary interactions can be conservative or highly non-conservative, significantly altering masses and orbital parameters.
• Observations of X-ray binaries and millisecond pulsars provide crucial constraints on neutron star and black hole masses and binary evolution pathways.
• Double compact object mergers (DNS, DBH) are natural outcomes of massive binary evolution and are key gravitational-wave sources with electromagnetic counterparts in some cases.
• Triple and higher-order multiplicity, dynamics in clusters, and natal kicks profoundly influence the formation and survival of compact-object binaries.