Evolving model for the continuum hot dust emission of eCB-SMBH. Left: computer simulation snapshot illustrating the eCB-SMBH configuration at the time instance of pericentre passage. M₁ and M₂ are SMBH loci, black ellipses are their orbits, B is the barycentre of the system, the blue circle is the sublimation ring bound to the M₂, the grey ring is the CBD, C is the centroid of the arc of the dust ring outside the CBD and the photo-centre of the continuum in GRAVITY’s K band. The masses of the SMBHs are M₁ = 6 × 10⁷ M_⊙ and M₂ = 4 × 10⁷ M_⊙, eCB-SMBH eccentricity is e = 0.5, and other orbital parameters are Ω₁ = 0.1°, ω₁ = 0.1°, Ω₂ = 180.1°, and ω₂ = 180.1°. See the main text for a description of the coordinate system. Right upper: schematic of the barycentric photo-centre displacement used in astrometry to detect a mass M₂ gravitationally bound in a two-body system with mass M₁. Bottom: nearby M₂ originates optical continuum F_c, which is then reprocessed by a dusty torus (yellow circle) into NIR emission F_nir in the K band (2.2 μm), commonly known as ‘dust continuum’. Because the dust ring (yellow circle segment) and CBD (blue circle segment) intersect, the photo-centre will be the centroid of the arc of the dust ring (yellow circle). The distance between the highest point of the dust-ring arc and M₂ is denoted by the symbol h. is the angular displacement of the photo-centre with respect to M₂.