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Abstract: The observed quasi-periodic doubly peaked
high-brightness flares in the 130-year long optical lightcurve of
blazar OJ 287 is best explained by its binary black hole (BBH) central
engine model, where a supermassive secondary black hole (BH) orbits a
more massive primary BH in a relativistic eccentric orbit. In this
model, the doubly peaked flares arise due to impacts of the secondary
BH with the accretion disk of the primary twice every orbit. This
model is successful in predicting the starting time of the last three
flares, and the latest one was observed during August 2019 with the
Spitzer space telescope. The observations of these predicted flares
strongly suggest the presence of an SMBHB that inspirals due to the
emission of nano-Hz gravitational waves (GWs) as the central engine of
OJ 287. Additionally, the high-resolution Very Long Baseline
Interferometry (VLBI) observations of OJ 287 reveal that its radio
jet's position angle (PA) exhibits systematic temporal
variations. These variations can arise from the precession of the
radio jet of OJ 287 due to the binary nature of its central engine. A
recent analysis reveals that the BBH central engine model, primarily
developed from the optical observations, can naturally explain the
temporal variations in the radio jet PA of OJ 287, observed at 86, 43,
and 15 GHz frequencies. Furthermore, the ongoing and future Global
mm-VLBI Array (GMVA) campaigns on OJ 287 have the potential to firmly
establish the validity of our model. These considerations make OJ 287
an excellent candidate for the nascent field of multimessenger nano-Hz
GW astronomy, expected to be inaugurated by the International Pulsar
Timing Array (IPTA) consortium during the present decade.
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