Abstract Sagittarius A* (Sgr A*) is a compact radio source at the Galactic center. Observations have confirmed that its mass is approximately (4.1 ± 0.4) × 10 6 M ⊙ , and Sgr A* is generally believed to be powered by gas accretion onto a supermassive black hole. Multifrequency radio observations of the pulsar J1745−2900, about 0.12 pc away from Sgr A*, reveal an unusually large Faraday rotation. Combined with X-ray observations, this indicates that there is a strong magnetic field (greater than 8 mG) leading to a low β plasma at large scales. We show that the gas starts to be captured by the black hole below tens of thousands of the Schwarzschild radii r S , where the gas pressure starts to dominate. Assuming that the accretion rate along magnetic fields at large scales decreases with the distance to the black hole following a power law, it is shown that, with an accretion disk below tens of r S , as revealed with the Event Horizon Telescope observations, there should be a supersonic wind above such a small accretion disk, and the accretion flow may be convection-dominated from tens of r S to tens of thousands of r S . Detailed modeling is warranted.
Yin et al. (Fri,) studied this question.