  Binary black hole (BH) central engine description for the unique blazar OJ
287 predicted that the next secondary BH impact-induced bremsstrahlung flare
should peak on 2019 July 31. This prediction was based on detailed general
relativistic modeling of the secondary BH trajectory around the primary BH and
its accretion disk. The expected flare was termed the Eddington flare to
commemorate the centennial celebrations of now-famous solar eclipse
observations to test general relativity by Sir Arthur Eddington. We analyze the
multi-epoch Spitzer observations of the expected flare between 2019 July 31 and
2019 September 6, as well as baseline observations during 2019 February-March.
Observed Spitzer flux density variations during the predicted outburst time
display a strong similarity with the observed optical pericenter flare from OJ
287 during 2007 September. The predicted flare appears comparable to the 2007
flare after subtracting the expected higher base-level Spitzer flux densities
at 3.55 and 4.49 $\mu$m compared to the optical R-band. Comparing the 2019 and
2007 outburst lightcurves and the previously calculated predictions, we find
that the Eddington flare arrived within 4 hours of the predicted time. Our
Spitzer observations are well consistent with the presence of a nano-Hertz
gravitational wave emitting spinning massive binary BH that inspirals along a
general relativistic eccentric orbit in OJ 287. These multi-epoch Spitzer
observations provide a parametric constraint on the celebrated BH no-hair
theorem.
