The BH-PSR Gravitational Molecule

TL;DR

This paper proposes the concept of a gravitational molecule formed by an axion-clouded black hole and a pulsar, developing a semi-analytical model to predict unique detection signals through pulsar timing and polarization observations.

Contribution

It introduces the novel idea of gravitational molecules involving axion clouds and develops a semi-analytical formalism to predict observable signals for detection.

Findings

Oscillating axion-cloud profiles predicted.

Unique timing and polarization signals identified.

Detection signals show correlated modulation patterns.

Abstract

While an axion-clouded black hole (BH) encounters a pulsar (PSR) or has a PSR companion, a "gravitational molecule" can be formed. In such a system, the axion cloud evolves at the binary hybrid orbitals, as it happens at microscopic level to electron cloud in a chemical molecule. To demonstrate this picture, we develop a semi-analytical formalism using the method of linear combination of atomic orbitals with an adiabatic approximation. An oscillating axion-cloud profile and a perturbed binary rotation, together with unique and novel detection signals, are then predicted. Remarkably, the proposed PSR timing and polarization observables, namely the oscillation of periastron time shift and the birefringence with multiple modulations, correlate in pattern, and thus can be properly combined to strengthen the detection.