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We use A-type stars selected from Sloan Digital Sky Survey data release 9photometry to measure the outer slope of the Milky Way stellar halo densityprofile beyond 50 kpc. A likelihood-based analysis is employed that models theugr photometry distribution of blue horizontal branch (BHB) and blue straggler(BS) stars. In the magnitude range, 18.5 < g < 20.5, these stellar populationsspan a heliocentric distance range of: 10 kpc < D_BS < 75 kpc, 40 kpc < D_BHB <100 kpc. Contributions from contaminants, such as QSOs, and the effect ofphotometric uncertainties, are also included in our modeling procedure. We findevidence for a very steep outer halo profile, with power-law index alpha ~ 6beyond Galactocentric radii r=50 kpc, and even steeper slopes favored (alpha ~6-10) at larger radii. This result holds true when stars belonging to knownoverdensities, such as the Sagittarius stream, are included or excluded. Weshow that, by comparison to numerical simulations, stellar halos with shallowerslopes at large distances tend to have more recent accretion activity. Thus, itis likely that the Milky Way has undergone a relatively quiet accretion historyover the past several Gyr. Our measurement of the outer stellar halo profilemay have important implications for dynamical mass models of the Milky Way,where the tracer density profile is strongly degenerate with totalmass-estimates.

Touching The Void: A Striking Drop in Stellar Halo Density Beyond 50 kpc