The First Gravitational Wave Catalog, GWTC-1

Abstract

On September 14, 2015, the earth was witness to one of universe’s loudest cataclysmic events: the collision of two black holes. The collision resulted in a perturbation in the very fabric of space time - a Gravitational Wave (GW). This event was brighter than all the stars in the universe combined. The effect of a GW manifests as a change in the lengths of objects. However, due to the weakly coupling nature nature of gravity, these length changes are miniscule, with strain amplitudes of the order of 10-21. Two extremely precise measuring instruments in Hanford, Washington and Livingston, Louisiana known as the Laser Interferometer Gravitational-Wave Observatories (LIGO) observed this event with a high significance. Code named GW150914, it was the first ever detection of GWs, a phenomenon predicted by Einstein’s theory of General Relativity. In summer 2017, LIGO was joined by Virgo, a similar interferometric detector in Pisa, Italy. Collectively, LIGO and Virgo have observed ten such GW events with high significances and these were recently published as the first comprehensive Gravitational Wave Transient Catalog or GWTC-1. GWTC-1 showcases Binary Black Hole (BBH) systems which cover large regions of parameter space. The total mass varies between 18 to 85 solar masses and distances vary from 320 to 2750 Megaparsec. It also includes systems with high spin and mass ratios which fold in interesting physics. I present the results from the catalog along with the inferred Astrophysics such as rates, formation channels and tests of General Relativity.