Long-term evolution of compact-object magnetic fields and ellipticity

Characterize the long-term evolution of compact-object magnetic fields and ellipticities, including the effects of magnetic-field decay and ellipticity evolution on continuous-gravitational-wave detectability and inferred birth magnetic-field distributions.

Background

The analysis constrains birth magnetic fields using continuous-gravitational-wave non-detections while conditioning on assumed ellipticity values and magnetic-field decay timescales. The reliability of those constraints depends on how these properties evolve over the lifetimes of compact objects. The paper identifies their long-term evolution as insufficiently understood and notes that alternative assumptions could alter the inferred magnetic-field distribution.

References

These constraints are conditional on assuming a fixed stellar ellipticity and a fixed magnetic-field decay timescale. However, long-term evolution of both quantities remains poorly understood, and different assumptions could modify the inferred birth magnetic field distribution.

— Probing magnetic fields of compact objects with continuous gravitational waves  (2609.04900 - Prabhu et al., 4 Sep 2026) in Section 1, Introduction

The distribution of ellipticities of compact objects remains uncertain.

— Probing magnetic fields of compact objects with continuous gravitational waves  (2609.04900 - Prabhu et al., 4 Sep 2026) in Section 2, subsection “Astrophysical Models and Magnetic Fields of Compact Objects,” paragraph “Ellipticity”

Several physical processes can contribute to magnetic-field decay, including Ohmic diffusion, Hall drift, and ambipolar diffusion \citep{GoldreichReisenegger1992,Xie2019TheEM} although estimates of the characteristic decay timescales remain uncertain \citep{Sang1987}.

— Probing magnetic fields of compact objects with continuous gravitational waves  (2609.04900 - Prabhu et al., 4 Sep 2026) in Section 2, subsection “Astrophysical Models and Magnetic Fields of Compact Objects,” paragraph “Magnetic field evolution”