Title: Why are LIGO/Virgo binary black holes so massive? 

Speaker: Xian Chen 

Abstract: Measuring the mass and distance of a gravitational wave (GW) source is a fundamental problem in GW astronomy. The issue is becoming even more pressing since LIGO and Virgo have detected massive black holes that in the past were thought to be rare, if not entirely impossible. The waveform templates used in the detection are developed under the assumption that the sources are residing in a vacuum, but astrophysical models predict that the sources could form in gaseous environments, move with relatively large velocity, or reside in the vicinity of supermassive black holes. In this talk, I will show how the above environmental factors could distort the GW signals and result in a biased estimation of the physical parameters. In particular, I will highlight the ubiquity of such a bias among the LIGO/Virgo/Kagra sources forming in active galactic nuclei. I will show how the supermassive black hole and the surrounding accretion disk will affect the GW signals of the merging binary black holes, by inducing the effect such as the Doppler shift, gravitational redshift, gravitational lensing, peculiar acceleration, and hydrodynamical friction.   If not appropriately accounted for, the above bias may alter our understanding of the formation and evolution of the LIGO/Virgo/Kagra black holes, as well as mislead our measurement of the cosmic expansion history of the universe. 

Bio: Prof. Xian Chen received his PhD from Peking University, and later moved on to the Kavli Institute for Astronomy and Astrophysics in Peking University, the Max-Planck Institute for Gravitational Physics in Germany, and the Pontificia Universidad Catolica de Chile for postdocs. In 2016 he came back to China and joined the Astronomy Department of Peking University. Prof. Chen’s research mainly focuses on the relativistic dynamics and radiation processes close to black holes. 

Time: 10:00-11:00, 14/June, Friday 

Venue: Room 508 (large seminar room), Department of Astronomy 

You can also access the colloquium via :

https://www.koushare.com/homepage/329883