  Galaxy-scale bars are expected to provide an effective means for driving
material towards the central region in spiral galaxies, and possibly feeding
supermassive black holes (BHs). Here we present a statistically-complete study
of the effect of bars on average BH accretion. From a well-selected sample of
50,794 spiral galaxies (with M* ~ 0.2-30 x 10^10 Msun) extracted from the Sloan
Digital Sky Survey Galaxy Zoo 2 project, we separate those sources considered
to contain galaxy-scale bars from those that do not. Using archival data taken
by the Chandra X-ray Observatory, we identify X-ray luminous (L_X >~ 10^41
erg/s) active galactic nuclei (AGN) and perform an X-ray stacking analysis on
the remaining X-ray undetected sources. Through X-ray stacking, we derive a
time-averaged look at accretion for galaxies at fixed stellar mass and star
formation rate, finding that the average nuclear accretion rates of galaxies
with bar structures are fully consistent with those lacking bars (Mdot_acc ~ 3
x 10^-5 Msun/yr). Hence, we robustly conclude that large-scale bars have little
or no effect on the average growth of BHs in nearby (z < 0.15) galaxies over
gigayear timescales.
