Photons generated by gravitional waves in the near-zone of a neutron star

TL;DR

This paper investigates how gravitational waves can convert into photons near neutron stars in magnetic fields, with potential implications for high-frequency gravitational wave detection.

Contribution

It analyzes photon conversion probabilities in both flat and curved spacetime near neutron stars, highlighting effects of magnetic field orientation and gravitational curvature.

Findings

Conversion probability estimated at 10^{-14} to 10^{-10}.

Higher frequency gravitational waves have increased conversion likelihood.

Curved spacetime slightly enhances photon conversion probability.

Abstract

When a gravitational wave or a graviton travels through an electric or magnetic background, it could convert into a photon with some probability. In this paper, a dipole magnetic field is considered as this kind of background in both the Minkowski spacetime and the curved spacetime in the near-zone of a neutron star. In the former case, we find that the graviton traveling vertically rather than parallel to the background magnetic field could be more effectively converted into an electromagnetic radiation field. In the latter case, we focus on the situation, in which the graviton travels along the radial direction near a neutron star. The radius of a neutron star is about ten kilometers, so the gravitational wave with long wavelength or low frequency may bypass neutron stars by diffraction. For high frequency gravitational wave, the conversion probability is proportional to the distance square as that in the static electric or magnetic background case. The smaller the inclination angle between the dipole field and the neutron star north pole is, the larger magnetic amplitude will be. The term that described curved spacetime will slightly enhance this kind of probability. We estimate that this value is about the order of $\sim 10^{-14}- 10^{-10}$. Therefore, it is expectable that this kind of conversion process may have a potential to open a window for observing high frequency gravitational waves.