Novel Astrophysical Constraints on Black Holes

Abstract

While black holes have captured both the public and scientific interest, they are still counted amongst the most mysterious objects in the Universe. In this dissertation, we study these objects from an astrophysical perspective. Black holes are active players in the astrophysical stage. They reshape their environments through the strength of their gravity, and their immense radiation is important even at cosmological distances. The first part of this dissertation is a study of the interplay between the supermassive black hole at the center of the Milky Way Galaxy and matter at the Galactic Center. We propose several astronomical observations that could detect the effects of this central black hole on its surrounding. As black holes are remarkable natural laboratories for gravitational physics, the second part of this dissertation focuses on leveraging astrophysical observables to test the validity of our current understanding of gravity. We study the repercussions of modifying general relativity on the astrophysical signals of both the plasma in the black hole accretion disk and stars in orbit around the black hole. The results of such tests will help determine the next steps in our pursuit for a theory of quantum gravity. Finally, the nascent field of gravitational waves astrophysics allows black holes to be studied in a novel way. The last part of this dissertation is concerned with using gravitational wave observables to study the population distribution of black holes. By utilizing data collected by gravitational wave observatories instead of conventional telescopes, we show that questions on the formation and evolution of black holes that were previously untenable can now be addressed. At the end of this dissertation, we will also discuss the possibility of observing the gravitational lensing of gravitational waves.