Formation and Evolution of Binary Neutron Stars

TL;DR

This paper models the formation and evolution of binary neutron stars, analyzing their orbital properties, birthrates, and connection to gamma-ray bursts, emphasizing the importance of common envelope efficiency and kick velocities.

Contribution

It provides a detailed evolutionary model of binary neutron stars, incorporating observational constraints and proposing scenarios for their formation and merger rates.

Findings

Estimated binary neutron star birthrate: 3.4 x 10^{-5} per year.

Merger rate aligns with gamma-ray burst estimates.

Efficient common envelope evolution and low-velocity kicks are crucial.

Abstract

The formation and evolution of binaries which contain two neutron stars or a neutron star with a black hole are discussed in detail. The evolution of the distributions in orbital period and eccentricity for neutron star binaries are studied as a function of time. In the model which fits the observations of high mass binary pulsars best the deposition of orbital energy into common envelopes has to be very efficient and a kick velocity distribution has to contain a significant contribution of low velocity kicks. The estimated age of the population has to be between several 100 Myr and 1 Gyr. The birthrate of binary neutron stars is about 3.4 10^{-5} per year (assuming 100% binarity) and their merger rate is about 2 x 10^{-5} per year. The merger rate of neutron star binaries is consistent with the estimated rate of gamma-ray bursts, if the latter are beamed into an opening angle of a few degrees. We argue that PSR B2303+46 is possibly formed in a scenario in which the common envelope is avoided while for the other three known high-mass binary pulsars a common envelope is required to explain their orbital period.