Inferring the Black Hole and Accretion Parameters of Sagittarius A ∗ from EHT Observations Using a Semianalytic Model
Year: 2026
Type: article
Abstract: The Event Horizon Telescope (EHT) Collaboration produced the first image of the apparent shadow of the central black hole of Sagittarius A ∗ (Sgr A ∗ ). Sgr A ∗ source structure varies significantly on timescales shorter than the duration of an observation, preventing improved data coverage through Earth rotation aperture synthesis. This rapid variability provides the opportunity to quantify intrinsic variability and separate time-variable emission features from stable signatures of strong gravity and the accretion environment. To infer unknown properties of Sgr A ∗ and its surrounding accretion flow, we perform Bayesian inference on a series of EHT data segments (“snapshots”). We directly fit parameters of a semianalytic emission model jointly with complex station gains to snapshot visibilities, then extract estimates of the time-averaged, persistent source structure and temporal variability by stacking snapshots in a Bayesian hierarchical model. This approach successfully reproduces parameters of general relativistic magnetohydrodynamic simulations using synthetic EHT observations. Even with physically motivated assumptions about the Sgr A ∗ environment, black hole spin and magnetic field parameters are poorly constrained by 2017 EHT observations. Our inference constrains other parameters, favoring a nearly face-on observer inclination ( θ o = 9 . ° 2 ± 3 . ° 6 ± v 11 . ° 6), an emission peak near the horizon ( R peak = 4.9 ± 0.1 ± v 0.5 GM / c 2 ), near-northern projected spin position angle ( p . a . = 7 . ° 3 ± 7 . ° 08 ± v 43 . ° 5 counterclockwise from vertical), and dominant emission 43 . ° 4 ± 2 . ° 0± v 5 . ° 9 above the equatorial plane, where we separate average structure uncertainty (±) from the impacts of temporal variability and model misspecification (± v ).
Source: The Astrophysical Journal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Awards: G1453181110, Track 4: Advanced CI Coordination Ecosystem: Monitoring and Measurement Services, G2299875479, G2888034965, G3185749182, G3562386289, Track 1: ACCESS Resource Allocations Marketplace and Platform Services (RAMPS), G4010157413, ACO: An Open CI Ecosystem to Advance Scientific Discovery (OpenCI), Collaborative Research: Experimental General Relativity using Radio Interferometry of a Black Hole Photon Ring, Track 3: COre National Ecosystem for CyberinfrasTructure (CONECT), G5367127336, G5464919783, G731264315, G766651960, Black Hole Initiative Phase 3, Track 2: Customized Multi-tier Assistance, Training, and Computational Help (MATCH) for End User ACCESS to CI, G878072758
OpenAlex ID: W7220944550