Exploring the High Energy Emission and Luminosity Mechanisms in Binary Black hole Systems Embedded in Active Galactic Nuclie
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Date
2025
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Saudi Digital Library
Abstract
In this project, I implement a theoretical astrophysics study to investigate the
potential electromagnetic (EM) signatures of binary black hole (BBH) systems
embedded within the accretion discs of active galactic nuclei (AGNs). The primary
objective is to model the spectral energy distribution (SED) of both the AGN and
the BBH system, with the aim of identifying physical conditions under which
the BBH-induced emission may become observationally distinguishable from the
dominant disc background. To construct realistic SEDs, the model incorporates
key radiative processes, including thermal blackbody emission from the AGN disc,
synchrotron radiation from relativistic electrons, and inverse Compton scattering
of seed photons. Systematic variations in viscosity, accretion rate, density, and
optical depth are explored to assess their influence on the spectral properties.
Special emphasis is also placed on transient flare events associated with BBH
activity and on scenarios where the AGN disc is intrinsically dimmed. These
conditions may enhance the visibility of BBH-driven high-energy emission, partic
ularly in the hard X-ray and gamma-ray regimes. The results suggest that during
low-luminosity phases of AGNs and BBH flaring episodes, the BBH emission can
dominate at high photon energies, providing a promising opportunity for detection.
This approach offers a complementary perspective to conventional methods, align
ing with emerging observational efforts to connect gravitational-wave detections
with electromagnetic counterparts. Although the model adopts several simplifying
assumptions, it provides valuable theoretical insights into the EM observability of
BBHsystems in AGN environments and contributes to the broader understanding
of multimessenger astrophysics.
Description
The structure of this thesis is as follows: I begin in Chapter 2 by reviewing the
essential background, including the physics of black holes and accretion discs,
mechanisms, such as angular momentum transport, disc rotation, and the role of
electromagnetic fields in disc dynamics. The chapter also introduces AGNs, high
lights the properties of their accretion discs, and explores how BBH systems may
become embedded within these environments. Then, it concludes with an over
view of potential electromagnetic counterparts resulting from BBH interactions
with the disc material.
Chapter 3 describes the methodology used in this study. I outline the theoretical
model for a non-rotating (Schwarzschild) black hole and construct the correspond
ing accretion disc model for an AGN. I then extend this framework to include a
BBH system embedded in the AGN disc, incorporating additional processes such
as synchrotron radiation and inverse Compton scattering. I also introduce a flaring
scenario in which the BBH emission becomes transiently visible, particularly when
the AGN disc is dimmed or obscured.
The results of these models are presented in Chapter 4, where I analyze the spectral
energy distributions (SEDs) produced by both the AGN disc and the embedded
BBH system. I examine how variations in parameters such as viscosity, accretion
rate, density, and optical depth affect the resulting spectra and the detectability
of the BBH component.
Chapter 5 discusses the implications of these findings, emphasizing the potential
observational strategies for distinguishing BBH-induced emission from the AGN
disc background. I also reflect on the broader relevance of this work in the context
of identifying EM counterparts to gravitational wave events.
In Chapter 6, I identify the current limitations of the modeling approach and
propose directions for future research. Finally, Chapter 7 summarizes the key
conclusions of the thesis and reflects on the significance and limitations of the
results presented
Keywords
Accretion disc, Active galactic nuclei, Binary Black Holes, High Energy
Citation
Mahnashi, L. (2025). Exploring the high-energy emissions and luminosity mechanisms in binary black hole system embedded in active galactic nuclei (Master’s thesis). University of Western Australia.