The Black Hole Explorer: Photon Ring Science, Detection and Shape Measurement

• DOI: 10.48550/arxiv.2406.09498
• Publication Date: 2024-08-23
• Authors: Lupsasca, Alexandru; Cárdenas-Avendaño...; Palumbo, Daniel C...; Johnson, Michael D.; Gralla, Samuel E.; Marrone, Daniel P.; Galison, Peter; Tiede, Paul; Keeble, Lennox
• Keywords: High Energy Physics - Theory; High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Theory (hep-th); FOS: Physical sciences; General Relativity and Quantum Cosmology (gr-qc); Astrophysics - High Energy Astrophysical Phenomena; General Relativity and Quantum Cosmology

General relativity predicts that black hole images ought to display a bright, thin (and as-of-yet-unresolved) ring. This "photon ring" is produced by photons that explore the strong gravity of the black hole, flowing along trajectories that experience extreme light bending within a few Schwarzschild radii of the horizon before escaping. The shape of the photon ring is largely insensitive to the precise details of the emission from the astronomical source surrounding the black hole and therefore provides a direct probe of the Kerr geometry and its parameters. The Black Hole Explorer (BHEX) is a proposed space-based experiment targeting the supermassive black holes M87* and Sgr A* with radio-interferometric observations at frequencies of 100 GHz through 300 GHz and from an orbital distance of ~30,000 km. This design will enable measurements of the photon rings around both M87* and Sgr A*, confirming the Kerr nature of these sources and delivering sharp estimates of their masses and spins.<br/>Submitted to SPIE Space Telescopes & Instrumentation<br/>