The Galactic Formation Rate of Eccentric Neutron Star-White Dwarf Binaries

TL;DR

This paper empirically estimates the Galactic formation rate of eccentric neutron star-white dwarf binaries, compares it with theoretical predictions, and discusses the uncertainties and consistency among different models.

Contribution

It provides the first empirical Galactic formation rate estimate for eccentric NS-WD binaries and compares it with various binary population synthesis predictions.

Findings

Empirical rate is about 7 per Myr, lower than theoretical estimates.

Uncertainties exceed an order of magnitude but rates are broadly consistent.

Empirical estimates are lower limits due to no beaming correction.

Abstract

In this paper we consider the population of eccentric binaries with a neutron star and a white dwarf that has been revealed in our galaxy in recent years through binary pulsar observations. We apply our statistical analysis method (Kim, Kalogera, & Lorimer 2003)and calculate the Galactic formation rate of these binaries empirically. We then compare our results with rate predictions based on binary population synthesis from various research groups and for various ranges of model input parameters. For our reference moel, we find the Galactic formation rate of these eccentric systems to be ~7 per Myr, about an order of magnitude smaller than results from binary evolution estimations. However, the empirical estimates are calculated with no correction for pulsar beaming, and therefore they should be taken as lower limits. Despite uncertainties that exceed an order of magnitude, there is significant overlap of the various rate calculations. This consistency lends confidence that our current understanding of the formation of these eccentric NS-WD binaries is reasonable.