  Stochastically-triggered photospheric light variations reaching $\sim$$40$
mmag peak-to-valley amplitudes have been detected in the O8Iaf supergiant V973
Scorpii as the outcome of two months of high-precision time-resolved
photometric observations with the BRIght Target Explorer (BRITE)
nanosatellites. The amplitude spectrum of the time series photometry exhibits a
pronounced broad bump in the low-frequency regime ($\lesssim$$0.9$ d$^{-1}$)
where several prominent frequencies are detected. A time-frequency analysis of
the observations reveals typical mode lifetimes of the order of $5-10$ days.
The overall features of the observed brightness amplitude spectrum of V973 Sco
match well with those extrapolated from two-dimensional hydrodynamical
simulations of convectively-driven internal gravity waves randomly excited from
deep in the convective cores of massive stars. An alternative or additional
possible source of excitation from a subsurface convection zone needs to be
explored in future theoretical investigations.
