Accretion onto the Supermassive Black Hole in M87

Chandra X-ray observations of the giant elliptical galaxy M87 resolve thethermal state of the hot interstellar medium into the accretion (Bondi) radiusof its central 3 10^9 Msun black hole. We measure the X-ray gas temperature anddensity profiles and calculate the Bondi accretion rate, Mdot_Bondi \sim 0.1Msun/yr. The X-ray luminosity of the active nucleus of M87 observed withChandra is L_{x, 0.5-7 \keV} \sim 7 \times 10^{40}erg/s. This value is muchless than the predicted nuclear luminosity, L_{Bondi} \sim 5 \times 10^{44}erg/s, for accretion at the Bondi rate with a canonical accretion radiativeefficiency of 10%. If the black hole in M87 accretes at this rate it must do soat a much lower radiative efficiency than the canonical value. Themultiwavelength spectrum of the nucleus is consistent with that predicted by anadvection-dominated flow. However, as is likely, the X-ray nucleus is dominatedby jet emission then the properties of flow must be modified, possibly byoutflows. We show that the overall energetics of the system are just consistentwith the predicted Bondi nuclear power. This suggests that either most of theaccretion energy is released in the relativistic jet or that the central engineof M87 undergoes on-off activity cycles. We show that, at present, the energydumped into the ISM by the jet may reduce the accretion rate onto the blackhole by a factor \propto (v_j/c_s)^{-2}, where v_j is the jet velocity and c_sthe ISM sound speed, and that this is sufficient to account for the low nuclearluminosity.Comment: emulateapj.sty, revised version, accepted by Ap