Black Holes and related projects

Black holes exist in various places in the Universe. The University of Athens Observatory performs follow-up observations in some special cases, where multi-wavelegth campaigns aim towards understanding their nature.

OJ 287 is a BL Lac object (blazar) at redshift z = 0.306 that has shown double-peaked bursts at regular intervals of ~12 yr during the last ~40 yr. Optical photopolarimetric monitoring data from 2005 to 2009 were studied, with the aim to analyse variability patterns and statistical properties of the optical polarization light curve. A strong preferred position angle in optical polarization was found after this study. The preferred position angle can be explained by separating the jet emission into two components: an optical polarization core and chaotic jet emission. This can possibly suggest that both the double-peaked bursts and the evolution of the optical polarization position angle could be explained as a sign of resonant accretion of magnetic field lines, a 'magnetic breathing' of the disc.

Artistic impression of blazar OJ 287 and a combined X-ray (Chandra) and radio image (VLA).

The study of the binary black hole OJ287 is still undergoing and so far it gave two publications in refereed journals:

Villforth et al. 'Variability and stability in blazar jets on time-scales of years: optical polarization monitoring of OJ 287 in 2005-2009', 2010, MNRAS, 402, 2087

Valtonen et al. 'Tidally Induced Outbursts in OJ 287 during 2005-2008', 2009, ApJ, 698, 781

Optical Monitoring Of The Active Black Hole V404 Cyg was started on 15 June 2015, after the SWIFT trigger for a possible gamma-ray busrt. This black hole binary was followed for the next 75 nights in optical R-band, utilizing the 0.40 m f/8 robotic and remote controlled telescope at the University of Athens Observatory.

The black hole binary system V404 Cyg gave a large outburst on June 15, 2015. An artistic representation of the binary system is given at top left figure, while a sample of an active photometric behavior is shown at top right figure. Continuous monitoring of this target from the University of Athens Observatory resulted in a 75-day long photometric light curve, part of which is shown in the bottom plot.

The study of V404 Cyg resulted so far in the following announcements:

Gazeas, K.; Vasilopoulos, G.; Petropoulou, M.; Sapountzis, K., 2015, ATel, 7650, 1

Vasilopoulos G, Gazeas, K., Petropoulou M., Sapountzis K., 2015, 12th HEL.AS. Conference, Thessaloniki, Greece

Team members

Collaboration between the University of Athens (Greece) and several other Institutes worldwide. Among them, the major collaborators are:

Kosmas Gazeas, Apostolos Mastichiadis, Konstantinos Sapountzis

University of Athens, GR 15784 Zografos, Athens, Greece

Maria Petropoulou

Purdue University, West Lafayette, Indiana, IN 47907-2036, USA

George Vasilopoulos

Max-Planck-Institut für extraterrestrische Physik, Garching bei Muenchen, D-85741, Germany

Stazsek Zola, Gopal Bhatta, Arti Goyal

Astronomical Observatory of the Jagiellonian University, Krakow, ul. Orla, 30-244, Poland

Alexios Liakos

National Observatory of Athens, Greece