Simulating the emission and outflows from accretion discs

The radio source Sagittarius A* (Sgr A*) is believed to be a hot, inhomogeneous, magnetized plasma flowing near the event horizon of the 3.6 × 10⁶ M_⊙ black hole at the galactic centre. At a distance of 8 kpc (≃ 2.5 × 10²² cm) the black hole would be among the largest black holes as judged by angular size. Recent observations are consistent with the idea that the millimetre and sub-millimetre photons are dominated by optically thin, thermal synchrotron emission. Anticipating future Very Long Baseline Interferometry (VLBI) observations of Sgr A* at these wavelengths, we present here the first dynamically self-consistent models of millimetre and sub-millimetre emission from Sgr A* based on general relativistic numerical simulations of the accretion flow. Angle-dependent spectra are calculated assuming a thermal distribution of electrons at the baryonic temperature dictated by the simulation and the accretion rate, which acts as a free parameter in our model. The effects of varying model parameters (black hole spin and inclination of the spin to the line of sight) and source variability on the spectrum are shown. We find that the accretion rate value needed to match our calculated millimetre flux to the observed flux is consistent with constraints on the accretion rate inferred from detections of the rotation measure. We also describe the relativistic jet that is launched along the black hole spin axis by the accretion disc and evolves to scales of ∼10³GMc^-2, where M is the mass of the black hole.