  The moderate spin estimate for the black hole at the center of the cool core
cluster H1821+643 motivates the completion of a story about this object's
origin and evolution that was in the making since the work by Blundell and
Rawlings over two decades ago as the first example of a massive black hole
accreting at near Eddington rates with an FRI jet. This elusive combination of
properties was explained in our 2010 model where we showed it to be part of a
small parameter space that includes X shaped radio galaxies. As an accreting
black hole that never experienced a counterrotating phase, H1821+643 is
constrained by theory to produce a jet for spin values between 0.1 and about
0.7 and an FRI jet for a slightly smaller range. The feedback from such a black
hole is not subject to a tilted jet and is why star formation rates remain high
in this cluster environment. The prediction is that H1821+643 is within
millions of years of becoming jetless.
