  M87 has been identified as a displaced supermassive black hole (SMBH)
candidate. We investigated this possibility by a temporal analysis of twelve
Adaptive-Optics assisted-VLT and HST images spanning twenty years. We found
that the centre of the isophotal fitting to the nuclear region of M87 -assumed
to mark the centre of mass of the galaxy- changes location depending on the
image and size of the image analysed. In an absolute frame of reference, the
change varies from 15 to 130 miliarcseconds (mas) with respect to the active
galactic nucleus (AGN), which remains stable within an uncertainty of $\pm$15
mas in both x and y axis. The temporal analysis of the results indicates that
the major displacements measured coincide with a powerful outburst that took
place between 2003 and 2007, where there was a flux increment in the nucleus
and the first knot of the jet. After the outburst, the isophotal centre remains
stable and is consistent with the AGN location. This suggests that the
displacements are artificially caused by a flux variation in the galaxy and
that the SMBH actually resides in the equilibrium position. We caution about
the determination of the galaxy photocentre by isophotal fitting in cases of
nuclear variability and/or presence of photometric irregularities, and advise a
long-term temporal analysis of the results to confirm possible displaced SMBHs.
