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Explain orbital period modulations in spider pulsars

Identify and characterize the physical mechanism(s) responsible for long-term orbital period variations and orbital modulations in spider pulsars, determining whether changes in the companion star’s gravitational quadrupole moment can fully account for the observed phenomena in systems such as PSR J1959+2048, J2051-0827, and J1544+4937.

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Background

Spider pulsars exhibit long-term variations in orbital periods and orbital elements that lack a definitive explanation.

While changes in the companion’s gravitational quadrupole moment are often invoked, the authors note that a conclusive mechanism has not been established and requires further investigation.

References

Orbital modulations have no definite explanation (see e.g. Corbet et al. 2022 [63]), although variation in the gravitational quadrupole moment of the companion star is often invoked as a mechanism (Applegate 1992 [72]; Applegate and Shaham 1994 [70]).

— The Spider Stellar Engine: a Fully Steerable Extraterrestrial Design? (2411.05038 - Vidal, 6 Nov 2024) in Section 4.5 (Other potential features and maneuvers)