Gravitational Wave Emission by Cataclysmic Variables: numerical models of semi-detached binaries

TL;DR

This paper compares numerical models of semi-detached binary stars with Roche models to assess gravitational wave emission's role in cataclysmic variable evolution and explains the period mismatch.

Contribution

It provides a systematic comparison showing Roche models are accurate within a few percent, suggesting other factors cause the period discrepancy.

Findings

Roche models closely match numerical models with minimal deviation

The minimum period of cataclysmic variables is reaffirmed by the models

Additional angular momentum loss mechanisms may explain the period mismatch

Abstract

Gravitational wave emission is considered to be the driving force for the evolution of short-period cataclysmic binary stars, making them a potential test for the validity of General Relativity. In spite of continuous refinements of the physical description, a 10% mismatch exists between the theoretical minimum period ($P_{\rm turn} \simeq 70$ min) and the short-period cut-off ($P_{\rm min} \simeq 80$ min) observed in the period distribution for cataclysmic variable binaries. A possible explanation for this mismatch was associated with the use of the Roche model. We here present a systematic comparison between self-consistent, numerically constructed sequences of hydrostatic models of binary stars and Roche models of semi-detached binaries. On the basis of our approach, we also derive a value for the minimum period of cataclysmic variable binaries. The results obtained through the comparison indicate that the Roche model is indeed very good, with deviations from the numerical solution which are of a few percent at most. Our results therefore suggest that additional sources of angular momentum loss or alternative explanations need to be considered in order to justify the mismatch.