High accuracy measurement of gravitational wave back-reaction in the OJ287 black hole binary

TL;DR

This paper measures the gravitational wave back-reaction in the OJ287 black hole binary, finding a slight deviation from standard predictions due to higher order effects, thus providing a new test of gravitational wave theory.

Contribution

It provides the first high-accuracy measurement of gravitational wave back-reaction in a supermassive black hole binary, including higher order tail effects.

Findings

Binary period decreasing at 36 days per century

Energy loss to gravitational waves is 6.5% less than predicted by quadrupolar emission

Higher order tail contributions explain the discrepancy

Abstract

Blazar OJ287 exhibits large thermal flares at least twice every 12 years. The times of these flares have been predicted successfully using the model of a quasi-Keplerian eccentric black hole binary where the secondary impacts the accretion disk of the primary, creating the thermal flares. New measurements of the historical light curve have been combined with the observations of the 2015 November/December flare to identify the impact record since year 1886, and to constrain the orbit of the binary. The orbit solution shows that the binary period, now 12.062 year, is decreasing at the rate of 36 days per century. This corresponds to an energy loss to gravitational waves that is 6.5 +- 4 % less than the rate predicted by the standard quadrupolar gravitational wave (GW) emission. We show that the difference is due to higher order gravitational radiation reaction terms that include the dominant order tail contributions.