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Aims: We resolve the small-scale structure around the high-mass hot coreregion G351.77-0.54 to investigate its disk and fragmentation properties.  Methods: Using ALMA at 690GHz with baselines exceeding 1.5km, we study thedense gas, dust and outflow emission at an unprecedented spatial resolution of0.06" (130AU@2.2kpc).  Results: Within the inner few 1000AU, G351.77 fragments into at least fourcores (brightness temperatures between 58 and 197K). The central structurearound the main submm source #1 with a diameter of ~0.5" does not showadditional fragmentation. While the CO(6-5) line wing emission shows an outflowlobe in the north-western direction emanating from source #1, the dense gastracer CH3CN shows a velocity gradient perpendicular to the outflow that isindicative of rotational motions. Absorption profile measurements against thesubmm source #2 indicate infall rates on the order of 10^{-4} to10^{-3}M_sun/yr which can be considered as an upper limit of the mean accretionrates. The position-velocity diagrams are consistent with a central rotatingdisk-like structure embedded in an infalling envelope, but they may also beinfluenced by the outflow. Using the CH_3CN(37_k-36_k) k-ladder with excitationtemperatures up to 1300K, we derive a gas temperature map of source #1exhibiting temperatures often in excess of 1000K. Brightness temperatures ofthe submm continuum never exceed 200K. This discrepancy between gastemperatures and submm dust brightness temperatures (in the optically thicklimit) indicates that the dust may trace the disk mid-plane whereas the gascould be tracing a hotter gaseous disk surface layer. In addition, we conduct apixel-by-pixel Toomre gravitational stability analysis of the central rotatingstructure. The derived high Q values throughout the structure confirm that thiscentral region appears stable against gravitational instability.

Fragmentation and disk formation in high-mass star formation: The ALMA view of G351.77-0.54 at 0.06" resolution