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tokens: for a triangle of interferometric baselines: For a symmetrical Gaussian intensity distributions on the sky, the visibility phase is expected to be zero and so is the closure phase. Any deviation from a zero closure phase will indicate the source deviation from a Gaussian or point-like structure, and this observable can in principle be used to compare the model and observed emission shape without reconstructing the radio maps. We have calculated the theoretical visibility closure phases. For the model with , which shows the crescent on the N side of the BH (see Fig. 8 ), the closure phases are positive; ,19,11,11, where the four values correspond to different time moments of the observation. The evolution is caused by the rotation of the Earth, and it is probing slightly different values. A typical observation duration is two to three hours. This is about three times shorter than the dynamical time scale of the source (8.5 h) with its BH mass, . For , for which the crescent is on the S side of the BH (Fig. 8 ), the closure phases are negative: , , , . In both cases, the values are consistent with the observed value: (Akiyama, priv. comm.). In summary, for the fiducial model RH100 (for both viewing angles of and ), visibility amplitudes and closure phases are roughly consistent with the preliminary observations of the M 87 core obtained by the EHT (visibility amplitudes and closure phases on a single VLBI triangle). Fig. 9 Theoretical visibility amplitudes along E-W ( left ) and N-S ( right ) baselines, computed for model RH100 with (solid lines) and 160(dashed lines). 4. Discussions Deriving the appearance of a jet in the direct vicinity of a SMBH is not straightforward. The jet formation mechanism, as well as particle acceleration in jets, is generally not understood well. Moreover, one has to take spacetime curvature into account, which affects the plasma dynamics and light propagation. Using GRMHD simulations of a weakly magnetized accretion flow, a jet appears naturally, and we calculate the appearance of the M 87 jet base at radio and millimeter wavelengths. For the electron heating, we assume that the electrons are weakly coupled to protons in the accretion disk and strongly coupled in the jet – a simple, but crucial concept that we have already used successfully to explain the appearance of the SMBH in the center of the Milky Way. Below we discuss our results in a context of observational constraints. We also discuss the model limitations. Fig. 10 Comparisons of the visibility amplitudes from our models and those from the EHT observations. The visibility amplitudes, computed at mm ( GHz), along three baselines (SMT-CARMA, SMT-HAWAII, and CARMA-HAWAII) are shown for model RH100 with (solid lines) and 160 (dashed lines). The distance between the VLBI stations is expressed in units of ( km). The observed visibility amplitudes (points) and the tracks are taken from Doeleman et al. (2012) . 4.1. Mass-accretion rate The accretion rate onto M 87