Lankeswar Dey (Tata Institute of Fundamental Research)

Lankeswar Dey Colloquium: Confirming the presence of a supermassive black hole binary in OJ 287

Online

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.