The M87 jet is experiencing extreme optical/UV
variability and very high energy emission that were never anticipated. HST-1,
a knot along the M87 jet located 1 arcsecond from the nucleus, has experienced
unusual and repeated flaring at all wavelengths during the last decade:
exceptional brightness variability for an individual component of an AGN jet.
On the left, Hubble Space Telescope observations revealed that the NUV
intensity of HST-1 increased by a factor of 100 between 1999 and 2005. This
is an unprecedented event that has only been observed in the M87 jet and has
serious implications for models of jet variability and unified schemes of
AGNs. Equivalent variability was recorded by Chandra, and the VLA. Similarly,
all three major Cherenkov observatories studying very high energy gamma-rays
reported flaring of M87 in the very high energy regime in 2005, 2008, and 2010.
The light-curves on the right hand side show flux measurements taken by 11