At the center of our Milky Way Galaxy lives a supermassive black hole called Sagittarius A* (Sgr A*) with a mass of 4 million solar masses. Sgr A* is a prototypical low-luminosity black hole with a very low mass accretion rate. Radiation from Sgr A* is best explained by a model in which the accreting gas is a two-temperature plasma with proton temperature approaching 10^12 K near the black hole and electron temperature exceeding 10^10 K. Event Horizon Telescope observations of Sgr A* have confirmed the key features of this model. Many low-luminosity black holes have relativistic jets, though surprisingly not Sgr A*. Computer simulations indicate that jets should form easily in hot accretion flows, provided the plasma is threaded by a strong magnetic field and the black hole spins rapidly.
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