  The capability of the Event Horizon Telescope (EHT) to image the nearest
supermassive black hole candidates at horizon-scale resolutions offers a novel
means to study gravity in its strongest regimes and to test different models
for these objects. Here, we study the observational appearance at 230 GHz of a
surfaceless black hole mimicker, namely a non-rotating boson star, in a
scenario consistent with the properties of the accretion flow onto Sgr A*. To
this end, we perform general relativistic magnetohydrodynamic simulations
followed by general relativistic radiative transfer calculations in the boson
star space-time. Synthetic reconstructed images considering realistic
astronomical observing conditions show that, despite qualitative similarities,
the differences in the appearance of a black hole -- either rotating or not --
and a boson star of the type considered here are large enough to be detectable.
These differences arise from dynamical effects directly related to the absence
of an event horizon, in particular, the accumulation of matter in the form of a
small torus or a spheroidal cloud in the interior of the boson star, and the
absence of an evacuated high-magnetization funnel in the polar regions. The
mechanism behind these effects is general enough to apply to other horizonless
and surfaceless black hole mimickers, strengthening confidence in the ability
of the EHT to identify such objects via radio observations.
