Evolutionary Period Changes for 25 X-ray Binaries and the Measurement of an Empirical Universal Law for Angular Momentum Loss in Accreting Binaries

TL;DR

This study measures period changes in 77 X-ray binaries and cataclysmic variables to empirically derive a universal law for angular momentum loss, challenging existing theoretical models and providing a new predictive framework.

Contribution

It introduces an empirical universal law for angular momentum loss in accreting binaries, based on direct measurements, and tests the inadequacy of traditional magnetic braking models.

Findings

Most systems' AML predictions deviate by over an order of magnitude from models.

The derived AML law fits observed data across different binary classes.

Three distinct AML laws are proposed for different period ranges, forming a universal description.

Abstract

I measure and collect timings of phase markers (like eclipse times) for the orbits of 25 X-ray binaries (XRBs) so as to calculate the steady evolutionary period change ($\dot{P}$). I combine these with my observed $\dot{P}$ measures from 52 cataclysmic variables (CVs). Further, I subtract out the contributions from gravitational radiation ($\dot{P}_{\rm GR}$) and mass transfer ($\dot{P}_{\rm mt}$), deriving the period change from the residual unknown angular momentum loss ($\dot{P}_{\rm AML}$=$\dot{P}$-$\dot{P}_{\rm GR}$-$\dot{P}_{\rm mt}$). I have $\dot{P}_{\rm AML}$ measures for 77 XRBs and CVs, with these being direct measures of the driver of binary evolution. The venerable Magnetic Braking Model (MBM) of binary evolution has its most fundamental predictions tested, with most systems having predictions wrong by over one order-of-magnitude. Other proposed mechanisms to explain the AML also fail, so we are left with no known mechanism that dominates the AML. An alternative path to the AML law is empirical, where my $\dot{P}_{\rm AML}$ measures are fitted to a power-law involving the fundamental binary properties. With this, the dominant AML law for systems with orbital periods ($P$) from 0.13--1.0 days is $\dot{P}_{\rm AML} = -1500\times10^{-12} P^{1.29} M_{\rm prim}^{2.75} M_{\rm comp}^{-1.00}\dot{M}^{0.43}_{-8}$, in appropriate units. Similar AML laws for binaries below the Period Gap and for binaries with $P$$>$1.0 day are derived. These three AML laws are of good accuracy and are the best representations of the actual evolution for all 77 XRBs and CVs of all classes, so the three taken together can be called `universal'.