SIGNALS FROM THE EDGE OF THE ABYSS: QUASI-PERIODIC OSCILLATIONS IN ACTIVE GALACTIC NUCLEI

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As matter spirals onto a black hole, it heats up and emits X-rays. The X-rays from this accretion disc encode information about how matter behaves in the region of highly curved space-time. The variability of the radiation is due to a number of noise processes, in addition to which there are - occasionally - Quasi-periodic oscillations (QPOs). The rapid timescales of these QPOs indicate they must be associated with something dynamic or radiative occurring very close to the black hole itself. Whilst QPOs have long been observed from the discs of X-ray binaries harbouring stellar mass black holes, it is only in the last 10 years or so that evidence has emerged that QPOs are also present in active galactic nuclei (AGN), harbouring supermassive black holes (SMBHs). Recent studies have indicated that the presence of QPOs may in fact be much more widespread in AGN that previously thought.