Modelling the accretion-ejection flow around the supermassive black hole at the centre of the Milky Way

Over the past decade, the study of compact objects has undergone substantial progress, with increasing focus on Sagittarius A* (Sgr A*), the supermassive black hole at the center of our galaxy and the closest of such objects to Earth. Due to its proximity, Sgr A* serves as an exceptional laboratory for relativistic astrophysics and general relativity. A major advancement in this field was achieved in 2022, when the Event Horizon Telescope (EHT) Collaboration released the first reconstructed image of Sgr A*’s immediate environment, enabling stronger constraints to be placed on state-of-the-art models.

The primary objective of this Master’s thesis is to reproduce, through analytical models, the observed spectrum, EHT image, and polarization quantities of Sgr A*'s close environment, using the general relativistic ray-tracing code GYOTO. The work performed with GYOTO has provided valuable insights into the impact of relativistic effects on the resulting spectra and synthetic images of the disk–jet plasma.

In this study, a new analytic disk + jet model is introduced, designed to reproduce both the characteristics of the observed spectrum, and the imaging observables reported by the EHT. An extensive exploration of the parameter space was conducted to identify the most influential parameters. Focus on optimizing the fit, while maintaining computational efficiency, was maintained throughout the project too. Although early simulations were affected by errors in the jet's density profile, these have since been resolved, resulting in a fully operational thick-disk + parabolic-jet model.