Accretion onto the supermassive black hole at the centre of our galaxy

Towards the end of his life, Ken Hines became fascinated with the physics of accretion onto the black hole at the centre of our Galaxy, a problem well suited to his extensive knowledge of magnetised, high-temperature plasmas. We spent several years formulating a strategy for analyzing the behaviour of ionised gas falling towards Sagittarius A*-as this object is known-but never quite finished the calculations. In this chapter, we will briefly review the circumstances that have made it possible for us to address this problem now, and demonstrate why Ken and I became so excited at the prospect of using the physics of accretion onto Sagittarius A* to probe the spacetime within a mere 20 Schwarzschild radii of its event horizon.