Much has been written about this remarkable object OJ+287 - a binary black hole system with a period of ~12 years.  I have been fortunate enough to be involved with several pro-am observing projects of OJ+287 since the 1990's, resulting in the following papers published as co-author...

 

Intensive Monitoring of OJ287.  Astronomy & Astrophysics  July 2000

 

The structure of the October/November 2005 outburst in OJ287 and the precessing Black Hole model.  Astronomy & Astrophysics, 477 2 (2008) 407-412

 

A massive binary black hole system in OJ287 and a test of general relativity.   NATURE (letters) Vol 452  April 17 2008 pg 851

 

Tidally induced outbursts in OJ 287 during 2005-2008. ApJ 698 (2009) 781-785 

 

Primary black hole spin in OJ287 as determined by the General Relativity centenary flare. ApJ,819, L37