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Date of Graduation
Active Galactic Nuclei (AGN) are the most luminous long-lived objects in the universe. The phenomenon of the immense luminosities we observe for AGN has interested physicists and astronomers for over a century and continues to fascinate scientists today. The work in this thesis aims to provide an introductory exploration of this phenomenon. This thesis uses a simple model of AGN accretion disks that was developed under the standard disk model proposed by Shakura & Sunyev in 1973 under the simplest assumptions. The model accurately demonstrates how physical parameters, such as the temperature, radiative flux, luminosity, and spectra, scale through an AGN accretion disk. The model is applied for characteristic mass accretion rates and masses of the supermassive black holes (SMBH) found at the center of most AGN. The dependencies of the disk's luminous power on these parameters are identified. We find that the inner regions of an AGN accretion disk are the hottest and therefore emit the greatest share of the disk’s luminosity. An accretion disk with a fixed mass accretion rate around a more massive SMBH is cooler than for a disk around a less massive one and is more luminous for greater accretion rates. The accretion disk spectra of AGN peak at ultraviolet (UV) wavelengths. For a fixed disk mass accretion rate, the accretion disks around less massive black holes are hotter and therefore have spectra that peak at shorter UV wavelengths and vice versa for spectra of accretion disks around more massive black holes. The shorter wavelengths in the observed spectrum are largely confined to arise and peak within inner regions of the disk where the temperature is hotter, whereas longer wavelengths are emitted from a broader range in the disk and peak in the outer disk where the temperature is cooler. We also applied a perturbation to the disk temperature through the inner section of the disk from the innermost circular stable orbit to r = 400 Rg to simulate with a simple model the highly variable nature of AGN. This model saw the shortest wavelengths contributing to the total luminosity of an accretion disk changed in their emission the most, as these wavelengths arise most prominently from the inner disk where our disk's temperature was perturbed, and the wavelengths which have significant contributions to the spectrum outside of r = 400 Rg fluctuated less.
Courtney, Imogen Jade, "The Luminous Power of Accretion Disks in Active Galactic Nuclei" (2023). Honors Theses. 3651.
Honors Thesis-Open Access