  The large-scale clustering of matter is impacted by baryonic physics,
particularly AGN feedback. Modelling or mitigating this impact will be
essential for making full use of upcoming measurements of cosmic shear and
other large-scale structure probes. We study baryonic effects on the matter
bispectrum, using measurements from a selection of state-of-the-art
hydrodynamical simulations: IllustrisTNG, Illustris, EAGLE, and BAHAMAS. We
identify a low-redshift enhancement of the bispectrum, peaking at $k\sim
3h\,{\rm Mpc}^{-1}$, that is present in several simulations, and discuss how it
can be associated to the evolving nature of AGN feedback at late times. This
enhancement does not appear in the matter power spectrum, and therefore
represents a new source of degeneracy breaking between two- and three-point
statistics. In addition, we provide physical interpretations for other aspects
of these measurements, and make initial comparisons to predictions from
perturbation theory, empirical fitting formulas, and the response function
formalism. We publicly release our measurements (including estimates of their
uncertainty due to sample variance) and bispectrum measurement code as
resources for the community.
