Theoretical Radio Signals from Radio-Band Gravitational Waves Converted from the Neutron Star Magnetic Field

TL;DR

This paper explores how strong magnetic fields in neutron stars can convert high-frequency gravitational waves into detectable radio signals, proposing new observational signatures and assessing detection capabilities of current and future radio telescopes.

Contribution

It provides a theoretical framework for detecting VHF gravitational waves via radio signals induced by neutron star magnetic fields, including specific signatures and sensitivity estimates for telescopes like FAST and SKA.

Findings

Strong neutron star magnetic fields enhance GW-to-radio conversion.

Identifies two signatures: transient and persistent signals.

FAST can approach detection thresholds for primordial black hole GWs.

Abstract

Gravitational waves (GWs) can convert into electromagnetic waves in the presence of a magnetic field via the Gertsenshtein-Zeldovich (GZ) effect. The characteristics of the magnetic field substantially affect this conversion probability. This paper confirms that strong magnetic fields in neutron stars significantly enhance the conversion probability, facilitating detectable radio signatures of very high-frequency (VHF, $\left(10^6-10^{11}\mathrm{~Hz}\right)$) gravitational waves. We theoretically identify two distinct signatures using single-dish telescopes (FAST, TMRT, QTT, GBT) and interferometers (SKA1/2-MID): transient signals from burst-like gravitational wave sources and persistent signals from cosmological background gravitational wave sources. These signatures are mapped to graviton spectral lines derived from quantum field theory by incorporating spin-2 and mass constraints, resulting in smooth, featureless profiles that are critical for distinguishing gravitational wave signals from astrophysical foregrounds. FAST attains a characteristic strain bound of $h_c<10^{-23}$, approaching $10^{-24}$ in the frequency range of $1-3\mathrm{~GHz}$ with a 6-hour observation period. This performance exceeds the $5 \sigma$ detection thresholds for GWs originating from primordial black holes (PBHs) and nears the limits set by Big Bang nucleosynthesis. Additionally, projections for SKA2-MID indicate even greater sensitivity. Detecting such gravitational waves would improve our comprehension of cosmological models, refine the parameter spaces for primordial black holes, and function as a test for quantum field theory. This approach addresses significant deficiencies in VHF GW research, improving detection sensitivity and facilitating the advancement of next-generation radio telescopes such as FASTA and SKA, which feature larger fields of view and enhanced gain.