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Constraints on high-frequency gravitational waves from graviton-photon conversion in the M87 galaxy

Aman Gupta1,2,3,*, Pratik Majumdar4,5,†, Sourov Roy1,‡, and Pratick Sarkar1,§

  • *Contact author: amann16.iitr@gmail.com
  • †Contact author: pratik.majumdar@saha.ac.in
  • ‡Contact author: tpsr@iacs.res.in
  • §Contact author: spsps2523@iacs.res.in
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Phys. Rev. D 114, 043038 – Published 17 August, 2026

DOI: https://doi.org/10.1103/hw1y-2m48

Abstract

High-frequency gravitational waves, particularly in the range f≳1010  Hz, represent a compelling probe of physics beyond the Standard Model. Due to the absence of direct detection methods in this frequency regime, alternative strategies may be pursued. One promising approach involves the conversion of gravitons into photons in the presence of magnetic fields, a process known as the inverse Gertsenshtein effect. In this study, we explore such graviton-to-photon conversions occurring within the magnetic field environment of the M87 galaxy, utilizing realistic models for the galactic magnetic field and plasma density structure. We use the broadband electromagnetic spectrum of M87, ranging from millimeter to TeV gamma rays, to search for hidden contributions from graviton-photon conversions. In the well-constrained frequency range 1010–1027  Hz, the lack of excess emission allows us to place improved bounds on the gravitational wave strain amplitude hc or on spectral energy density Ωgwh2. We find that our results from M87 yield substantially stronger constraints compared to existing bounds derived from Milky Way magnetic field considerations, with improvements ranging from one to five orders of magnitude depending on the frequency band, thereby enhancing the prospects for probing high-frequency gravitational wave backgrounds through indirect electromagnetic signatures.

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Phys. Rev. D 114, 043038– Published 17 August, 2026
  • Received 11 April 2026
  • Accepted 27 July 2026
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