Lunch talk on Jan. 6, 2025

Measuring the Hubble Constant with Binary Black Holes in Active Galactic Nuclei

Speaker: Alejandro Torres Orjuela (BIMSA)

Venue: SWIFAR Building 2111

Time: 12:45 PM, Monday, Jan. 6, 2025

Abstract: 

Cosmology has made significant advances in recent decades giving us an almost complete picture of the evolution of the universe from short after its formation until today. Nevertheless, it faces a simple but crucial problem in the Hubble tension – the significant difference in the measurements of the Hubble constant depending on wether it is measured with direct (low-redshift) or indirect (high-redshift) methods. There is great hope that standard sirens – gravitational wave (GW) sources with an electromagnetic (EM) counterpart – will help resolve the Hubble tension and binary black holes (BBHs) in active galactic nuclei (AGNs) have emerged as some of the most promising sources in this case. BBHs in AGNs differ significantly from the standard case of a source in vacuum due to the effects of the environemnt – the interaction of the gas with the binary, the orbital motion of the source around the supermassive black hole in the center of the AGN, and its gravitational potential. Despite this fact, most studies treat BBHs in AGN discs like vacuum sources which can lead to significant errors when measuring the Hubble constant. In this talk, I discuss how the environment influences GW detection as well as the measurement of the Hubble constant. I show for the GW190521 and its EM counterpart ZTF19abanrhr how measurments can be corrected by accounting for the effects of the environment and give a brief overview of the importance of similar corrections for other (future) events.

Report PPT:  SWIFAR_Alejandro Torres-Orjuela.pdf