  The effects of $\Delta$ isobars on the equation of state of dense matter and
structure of compact stars (CSs) are explored within the covariant density
functional theory and confronted with the data on tidal deformability (TD)
extracted from the GW170817 event. We show that the presence of $\Delta$
isobars substantially softens the tension between the predictions of the
hypernuclear density functionals and the inference from the observations of
relatively small radius and small TD of canonical mass CSs. The TDs deduced
from GW170817 are compatible with the existence of hypernuclear CSs containing
an admixture of $\Delta$ isobars. We thus argue that the GW170817 event is
consistent with a merger of a binary CS system having both strangeness
(hyperons) and $\Delta$ isobars in the stellar core.
