Bryan studies the mechanisms behind the suppression of star formation, i.e. quiescence, in galaxies. The number of these quiescent galaxies has been increasing gradually throughout the history of the universe. Bryan’s research addresses which galaxies become quiescent and when, how quickly this happens, and the physical mechanisms responsible for this transformation. For massive galaxies, black hole-driven feedback is thought to play a critical role in this process. Bryan works on developing a more comprehensive theoretical understanding of how this form of feedback may influence the galaxy-baryon cycle as well as how it may affect the observed trends and correlations found in galaxy populations.