Black Holes in Active Galactic Nuclei

TL;DR

This paper discusses the binary black hole system in the quasar OJ287, using over a century of optical data to test predictions of General Relativity and the black hole no-hair theorem in a strong gravitational field.

Contribution

It provides the first detailed orbital analysis of a binary black hole in an active galactic nucleus, testing higher order Post Newtonian effects and the no-hair theorem with observational data.

Findings

Confirmed the binary nature of OJ287 through periodic pulses.

Measured a high precession rate of 39.1 degrees per orbit.

Supported the black hole no-hair theorem with a parameter close to 1.

Abstract

Supermassive black holes are common in centers of galaxies. Among the active galaxies, quasars are the most extreme, and their black hole masses range as high as to $6\cdot 10^{10} M_\odot$. Binary black holes are of special interest but so far OJ287 is the only confirmed case with known orbital elements. In OJ287, the binary nature is confirmed by periodic radiation pulses. The period is twelve years with two pulses per period. The last four pulses have been correctly predicted with the accuracy of few weeks, the latest in 2007 with the accuracy of one day. This accuracy is high enough that one may test the higher order terms in the Post Newtonian approximation to General Relativity. The precession rate per period is $39^\circ.1 \pm 0^\circ.1$, by far the largest rate in any known binary, and the $(1.83\pm 0.01)\cdot 10^{10} M_\odot$ primary is among the dozen biggest black holes known. We will discuss the various Post Newtonian terms and their effect on the orbit solution. The over 100 year data base of optical variations in OJ287 puts limits on these terms and thus tests the ability of Einstein's General Relativity to describe, for the first time, dynamic binary black hole spacetime in the strong field regime. The quadrupole-moment contributions to the equations of motion allows us to constrain the `no-hair' parameter to be $1.0\:\pm\:0.3$ which supports the black hole no-hair theorem within the achievable precision.