Possible tidal dissipation in millisecond pulsar binaries

TL;DR

This paper investigates the potential impact of tidal dissipation on the orbital decay of millisecond pulsar binaries, challenging the assumption that it is negligible and exploring its implications for gravitational tests.

Contribution

It provides the first detailed analysis of tidal dissipation effects on pulsar binary orbital decay, including deriving tidal parameters and comparing models with observational data.

Findings

Tidal dissipation can explain residual orbital decay in some millisecond pulsar binaries.

The Love number of the companion in PSR J1227-4853 is estimated as 0.177.

A weak correlation between tidal parameters and orbital period suggests tidal effects during the recycled stage.

Abstract

The post-Keplerian(PK) parameters inferred from pulsar timing provide a convenient way to test Einstein's general theory of relativity. However, before obtaining a pure orbital decay $\dot{P}_b$ induced by gravitational wave radiation, which is one of the PK parameters, a number of factors need to be accounted for carefully. The effect of tidal dissipation on $\dot{P}_b$ has been thought of as negligible. Here, we investigate the data for possible effects of tidal dissipation on $\dot{P}_b$. The possibility of the tidal dissipation as a contributor to $\dot{P}_b$ in a large sample of millisecond pulsar binaries is investigated in detail. We collected a large sample of pulsar binaries with measured $\dot{P}_b$. All of the systems are millisecond pulsars. The residual $\dot{P}^{Res}_b$ of these systems was obtained by subtracting the three normal effects, that is to say the effect of Shklovskii, line-of-sight acceleration, and gravitational radiation. Assuming that tidal dissipation is responsible for such a residual $\dot{P}^{Res}_b$, the tidal parameters of these systems can be calculated and compared with the tidal models. The residual $\dot{P}^{Res}_b$ is distributed over the half positive and half negative. The dynamical tidal model can explain the residual $\dot{P}_b$ of millisecond pulsar-white dwarf binaries. And the Love number of the main-sequence companion of \object{PSR J1227-4853} can be derived as a reasonable value $k_2=0.177^{+0.098}_{-0.058}$ with the equilibrium tidal model. Those results are compatible with the scenario of tidal dissipation. Additionally, a weak correlation between the tidal parameter and orbital period is revealed, likely originating in the tidal process of the recycled stage which is worthy of further investigation.