Testing black hole no-hair theorem with OJ287
  We examine the ability to test the black hole no-hair theorem at the 10% level in this decade using the binary black hole in OJ287. In the test we constrain the value of the dimensionless parameter q that relates the scaled quadrupole moment and spin of the primary black hole: q2 = -q 2 . At the present we can say that q = 1 \pm 0.3 (one), in agreement with General Relativity and the no-hair theorems. We demonstrate that this result can be improved if more observational data is found in historical plate archives for the 1959 and 1971 outbursts. We also show that the predicted 2015 and 2019 outbursts will be crucial in improving the accuracy of the test. Space-based photometry is required in 2019 July due the proximity of OJ287 to the Sun at the time of the outburst. The best situation would be to carry out the photometry far from the Earth, from quite a different vantage point, in order to avoid the influence of the nearby Sun. We have considered in particular the STEREO space mission which would be ideal if it has a continuation in 2019 or LORRI on board the New Horizons mission to Pluto. 
M. J.Valtonen, S. Mikkola, H. J.Lehto, A. Gopakumar, R. Hudec and J.   Polednikova
astro-ph.CO