  In a tidal disruption event (TDE), a star is destroyed by the gravitational
field of a supermassive black hole (SMBH) to produce a stream of debris, some
of which accretes onto the SMBH and creates a luminous flare. The distribution
of mass along the stream has a direct impact on the accretion rate, and thus
modeling the time-dependent evolution of this distribution provides insight
into the relevant physical processes that drive the observable properties of
TDEs. Analytic models that only account for the ballistic evolution of the
debris do not capture salient and time-dependent features of the mass
distribution, suggesting that fluid dynamical effects significantly modify the
debris dynamics. Previous investigations have claimed that shocks are primarily
responsible for these modifications, but here we show -- with high-resolution
hydrodynamical simulations -- that self-gravity is the dominant physical
mechanism responsible for the anomalous (i.e., not predicted by ballistic
models) debris stream features and its time dependence. These high-resolution
simulations also show that there is a specific length scale on which
self-gravity modifies the debris mass distribution, and as such there is
enhanced power in specific Fourier modes. Our results have implications for the
stability of the debris stream under the influence of self-gravity,
particularly at late times and the corresponding observational signatures of
TDEs.
