Reconstruction of Static Black Hole Images Using Simple Geometric Forms

Abstract

General Relativity predicts that the emission close to a black hole must be lensed by its strong gravitational field, illuminating the last photon orbit. This results in a dark circular area known as the black hole 'shadow'. The Event Horizon Telescope (EHT) is a (sub)mm VLBI network capable of Schwarzschild-radius resolution on Sagittarius A* (or Sgr A*), the 4 million solar mass black hole at the Galactic Center. The goals of the Sgr A* observations include resolving and measuring the details of its morphology. However, EHT data are sparse in the visibility domain, complicating reliable detailed image reconstruction. Therefore, direct pixel imaging should be complemented by other approaches. Using simulated EHT data from a black hole emission model we consider an approach to Sgr A* image reconstruction based on a simple and computationally efficient analytical model that produces images similar to the synthetic ones. The model consists of an eccentric ring with a brightness gradient and a two-dimensional Gaussian. These elemental forms have closed functional representations in the visibility domain, which lowers the computational overhead of fitting the model to the EHT observations. For model fitting we use a version of the Markov chain Monte-Carlo (MCMC) algorithm based on the Metropolis-Hastings sampler with replica exchange. Over a series of simulations we demonstrate that our model can be used for determining geometric measures of a black hole, thus providing information on the shadow size, linking General Relativity with accretion theory.

References in corpus (9)

• Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
• Detection of the Intrinsic Size of Sagittarius A* through Closure Amplitude Imaging (includes Online Supporting Material)
• Estimating the Parameters of Sgr A*'s Accretion Flow Via Millimeter VLBI
• Frequency-Dependent Shift in the Image Centroid of the Black Hole at the Galactic Center as a Test of General Relativity
• A geometric crescent model for black hole images
• The Galactic Center Weather Forecast
• Constraining the Structure of Sagittarius A*'s Accretion Flow with Millimeter-VLBI Closure Phases
• Using Millimeter VLBI to Constrain RIAF Models of Sagittarius A*
• Testing the No-Hair Theorem with Sgr A*

Cited by in corpus (5)

• First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
• Testing General Relativity with the Event Horizon Telescope
• On the approximation of the black hole shadow with a simple polar curve
• Discretization and Filtering Effects on Black Hole Images Obtained with the Event Horizon Telescope
• How narrow is the M87* ring? I. The choice of closure likelihood function