  M 87 is the best target for studying black hole accretion and jet formation.
Reanalysis of the EHT public data at 230 GHz shows a core-knots structure at
the center and jet features (Miyoshi et al. 2022a). We here compare this with
the new results of GMVA at 86 GHz showing a spatially resolved central core (Lu
et al. 2023a). There are similarities and differences between the two. At 86
GHz,"two bright regions" are seen on the ring in the core."Core-Knot-Westknot",
triple structure in the 230 GHz image shows apparent appearance of two peaks
similar to the "two bright regions" when convolved with the GMVA beam. This
similarity suggests that both frequencies reveal the same objects in the core
area. Protrusions are observed on both the south and north sides of the core at
both frequencies, becoming prominent and wing-like at 230 GHz. The 86 GHz image
shows a triple ridge jet structure, while the 230 GHz image shows only a bright
central ridge with two roots. Both frequencies show a shade between the core
and the central ridge. To detect the faint features from the EHT2017 data, we
found that the use of all baseline data is essential. Using all including the
ultrashort baseline data, revealed the jet and faint structures. Without the
ultrashort baselines, these structures were not detectable. The lack of
detection of any faint structures other than the ring in the M 87 data by the
EHTC is presumably due to the exclusion of ultrashort baselines from their
analysis.
