Wednesday Colloquium


"Comparison of LIGO/Virgo data with stellar and binary evolution models"

Krzysztof Belczyński (NCAC, Warsaw)

I will discuss the astrophysical importance of the recent LIGO/Virgo direct detections of BH-BH, BH-NS and NS-NS in gravitational-waves. For 10 BH-BH merger detections new models of isolated classical binary evolution can recover LIGO/Virgo merger rates, BH masses and spins. This still does not exclude other formation channels, and we do not know yet how these BH-BH mergers have formed. However, the recent detection of NS-NS merger in an old elliptical host galaxy can not be reproduced by any major formation channel. Despite the fact that the exact origin of LIGO/Virgo sources is not yet known, several astrophysical implications are beginning to emerge.


"Modeling 2009-2013 observations of M87* with an asymmetric ring"

Maciej Wielgus (Harvard Smithonian CfA)

The Event Horizon Telescope (EHT) has delivered first resolved images of M87*, a supermassive black hole in a center of the M87 galaxy. These results are based on the 230 GHz observations performed in April 2017. Dedicated tools were developed to facilitate the modeling and analysis of the EHT 2017 data set in a Markov chain Monte Carlo (MCMC) framework, demonstrating that the source morphology can be very well represented by a crescent. More data, from different time epochs, are required to investigate the long term stability of the source parameters, such as its diameter and orientation. To address that need, we analyze archival data from proto-EHT 230 GHz observations of M87* in the framework utilized for the 2017 data analysis. We fit geometric models to the observations taken in 2009, 2012 (published in the past) and 2011, 2013 (not published previously), exploring the parameter space with a MCMC algorithm. We validate the procedure using synthetic data. While the archival data sets are far less constraining than the 2017 observations, we obtain measurements of the source diameter and orientation. Variations of the M87* morphology in the 2009--2017 period are found to be roughly consistent with the predictions of general relativistic magnetohydrodynamic simulations of a turbulent accretion flow.