http://arxiv.org/abs/2212.03020
It is known that magnetic fields exist near black holes and photons can go around the black holes due to strong gravity. Utilizing these facts, we can probe hypothetical pseudoscalar particles, so-called axions. In fact, photons can be converted into axions when they propagate in a magnetic field. The conversion of such photons into axions leads to a dimming of the photon ring around the black hole shadow. We show that the photon ring dimming can occur efficiently for supermassive black holes. Remarkably, it turns out that the maximal dimming rate of the photon ring is 25%. In the case of M87$^*$, the dimming could be around 10% in the X-ray and gamma-ray bands. The frequency band and the magnitude of the dimming depend on the axion-photon coupling and axion mass. Hence, the distorted spectrum of the photon ring provides a novel tool for detecting axions.
K. Nomura, K. Saito and J. Soda
Wed, 7 Dec 22
2/74
Comments: 17 pages, 4 figures