Molecular absorption in variable brightest cluster galaxies

Supermassive black holes devour immense quantities of mass from their surroundings, and in doing so have a profound effect upon the galaxy they reside in. Most of the mass they consume is thought to be in the form of cold molecular gas clouds, but the ways in which these form and migrate to the supermassive black hole are still uncertain. This thesis aims to reveal the properties of molecular clouds in the cores of the Universe’s most massive galaxies through observations - determining their typical mass, temperature, kinematics, and the manner in which they find their way into the galaxies. This is achieved by a new observing technique which takes advantage of the bright and compact active galactic nucleus which encompasses the central supermassive black hole of many large galaxies. As molecular clouds pass in front of this region, they cast shadows. These shadows are signatures of the clouds' properties and make it possible to study them, often individually. These studies are also linked to the variability of active galactic nuclei, which is directly dependant on supermassive black hole accretion.