Elliptical galaxy nuclei are the sites of the largest black holes known , but typically show little or no nuclear activity .
We investigate this extreme quiescence using Chandra X-ray Observatory observations of the giant elliptical galaxies NGC 1399 , NGC 4472 , and NGC 4636 .
The unique Chandra imaging power enables us to place upper limits of 7.3 , 15 and 28 \times 10 ^ { -9 } the Eddington luminosity for the \sim 10 ^ { 8 } -10 ^ { 9 } M _ { \odot } black holes in NGC 1399 , NGC 4472 , and NGC 4636 , respectively .
The corresponding radiative efficiencies in this band are 4.1 , 24 , and 620 \times 10 ^ { -6 } using Bondi accretion rates derived from the Chandra hot interstellar gas surface brightness profiles .
These limits are inconsistent with basic advection-dominated accretion flow ( ADAF ) models for NGC 1399 and NGC 4472 , indicating accretion onto the black hole at \lesssim 10 % of the Bondi rate .