Dynamical Tides in Eccentric Binaries Containing Massive Main-Sequence Stars: Analytical Expressions

TL;DR

This paper derives analytical formulas for tidal interactions in eccentric binaries with massive main-sequence stars, aiding understanding of their orbital evolution and implications for merging compact-object systems.

Contribution

It provides new analytical expressions for tidal torque and energy transfer applicable to arbitrary eccentricities and stellar rotation rates in such binaries.

Findings

Analytical expressions explain observed orbital decay in PSR J0045-7319.

Retrograde and differential rotation in the B-star are needed to match observations.

Larger convective cores due to rotation or mass transfer may influence tidal dissipation.

Abstract

Tidal evolution of eccentric binary systems containing at least one massive main-sequence (MS) star plays an important role in the formation scenarios of merging compact-object binaries. The dominant dissipation mechanism in such systems involves tidal excitation of outgoing internal gravity waves at the convective-radiative boundary and dissipation of the waves at the stellar envelope/surface. We have derived analytical expressions for the tidal torque and tidal energy transfer rate in such binaries for arbitrary orbital eccentricities and stellar rotation rates. These expressions can be used to study the spin and orbital evolution of eccentric binaries containing massive MS stars, such as the progenitors of merging neutron star binaries. Applying our results to the PSR J0045-7319 system, which has a massive B-star companion and an observed, rapidly decaying orbit, we find that for the standard radius of convective core based on non-rotating stellar models, the B-star must have a significant retrograde and differential rotation in order to explain the observed orbital decay rate. Alternatively, we suggest that the convective core may be larger as a result of rapid stellar rotation and/or mass transfer to the B-star in the recent past during the post-MS evolution of the pulsar progenitor.