  We set out to bridge the gap between regular black-hole spacetimes and
observations of a black-hole shadow by the Event Horizon Telescope. We explore
modifications of spinning and non-spinning black-hole spacetimes inspired by
asymptotically safe quantum gravity which features a scale dependence of the
Newton coupling. As a consequence, the predictions of our model, such as the
shadow shape and size, depend on one free parameter determining the curvature
scale at which deviations from General Relativity set in. In more general
new-physics settings, it can also depart substantially from the Planck scale.
In this case, the free parameter is constrained by observations, since the
corresponding curvature scale is significantly below the Planck-scale. The
leading new-physics effect can be recast as a scale-dependent black-hole mass,
resulting in distinct observational signatures of our model. As a concrete
example, we show that two mass-measurements, extracted from the size of the
shadow and from Keplerian orbital motion of stars, allow to distinguish the
classical from the modified, regular black-hole spacetime, yielding a bound on
the free parameter. For spinning black holes, we further find that the
singularity-resolving new physics puts a characteristic dent in the shadow.
Finally, we argue, based on the underlying physical mechanism, that the effects
we derive could be generic consequences of a large class of quantum-gravity
theories.
