The brightness of the blazar OJ 287 has been regularly determined by us since the beginning of the research project "AGN-Monitoring". From the end of March 2020 we could observe an increase in brightness of this object, which peaked on April 26th of 2020. During these almost six weeks the brightness of this Active Galaxy Nucleus (AGN) increased by 1.25 magnitudes and decreased again afterwards.

This discovery was published in an ad-hoc announcement in Astronomer's Telegram worldwide. The Astronomer's Telegram is an Internet platform where significant astronomical events are quickly spread around the world so that they are documented and can be verified all over the globe. The students' measurements and evaluations matched very well with the observations of other working groups.

The monitoring of AGN at the Hans Haffner Observatory is carried out in coordination with the MAGIC collaboration, which operates a telescope system for gamma radiation on the Canary Island of La Palma. Unfortunately, parallel measurements could not be performed there due to the corona shut-down.

OJ 287 is located in the constellation of Cancer, is 3.5 billion light years away from earth and contains one of the largest known black holes, with 18 billion solar masses. This supermassive black hole is orbited by a smaller second black hole, which weighs about 100 million solar masses and takes about 12 years to orbit. During this orbit, it passes twice through the accretion disk of the central black hole, which leads to strong disturbances of the jet emanating from it. This is also reflected in brightness fluctuations observed from earth.

Due to the brightness outbursts it was possible to determine the masses of this binary system of black holes very precisely. The orbit of the small black hole could also be determined very precisely. It was also found that the two black holes converge and merge in 10 000 years. Therefore, OJ 287 is also an interesting object for measuring gravitational waves with the planned space interferometer LISA.

The project "AGN-Monitoring" in cooperation with the Chair of Astronomy of the University of Würzburg and the Chair of Experimental Particle Physics 5b of the Technical University Dortmund exists since 2012.

The announcement of the brightness outburst by the student team of the Hans-Haffner-Observatory can be read here:

http://www.astronomerstelegram.org/?read=13677