Universal $10^{20}$Hz stochastic gravitational waves from photon spheres of black holes

TL;DR

Photon spheres of supermassive black holes produce a universal high-frequency stochastic gravitational wave background at around 10^{20}Hz via photon-graviton conversion, with a potentially detectable density parameter of 10^{-12}.

Contribution

This work predicts a universal frequency for gravitational waves from black hole photon spheres and estimates their density, highlighting a new high-frequency gravitational wave source.

Findings

Frequency of gravitational waves is approximately 10^{20}Hz.

Density parameter of these waves could be around 10^{-12}.

Detection methods for such high-frequency waves are worth exploring.

Abstract

We show that photon spheres of supermassive black holes generate high-frequency stochastic gravitational waves through the photon-graviton conversion. Remarkably, the frequency is universally determined as $m_e\sqrt{m_e /m_p} \simeq 10^{20} \text{Hz}$ in terms of the proton mass $m_p$ and the electron mass $m_e$. It turns out that the density parameter of the stochastic gravitational waves $ \Omega_{ \text{gw}}$ could be $ 10^{-12}$. Since the existence of the gravitational waves from photon spheres is robust, it is worth seeking methods of detecting high-frequency gravitational waves around $10^{20}$Hz.