Top: the origin of luminosity bursts. The central 3 au of the disk just before ((a), (c), and (e)) and during ((b), (d), and (f)) a protostellar accretion burst. Rows from top to bottom show gas surface densities, gas temperatures, and turbulent dynamical viscosities. The arrow indicates a local density disturbance that produces viscous heating in the inner disk. Bottom: total luminosities (accretion plus photospheric) and evaporated dust masses as a function of time from protostellar birth.