자료유형  

 학위논문

Control Number  

0017165026

International Standard Book Number  

9798384462507

Dewey Decimal Classification Number  

520

Main Entry-Personal Name  

Neustadt, Jack Madison Marshall.

Publication, Distribution, etc. (Imprint  

[S.l.] : The Ohio State University., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

306 p.

General Note  

Source: Dissertations Abstracts International, Volume: 86-04, Section: B.

General Note  

Advisor: Kochanek, Christopher S.;Stanek, Krzysztof Z.

Dissertation Note  

Thesis (Ph.D.)--The Ohio State University, 2024.

Summary, Etc.  

요약Accretion onto a supermassive black hole (SMBH) is the most radiatively-efficient processes in the Universe, capable of producing more radiation in a region the size of the Solar System than is produced in an entire galaxy. When this happens, the system surrounding the SMBH is called an active galactic nucleus (AGN). AGNs have tremendous impact on star formation and the growth of galaxies as well as being unique probes of many important astrophysical processes. Indeed, understanding the growth of SMBHs and the AGNs that drive this growth is one of the highlighted topics in the 2020 Astronomy & Astrophysics Decadal Survey.AGNs are systems with multiple components, and the most important of these is the accretion disk surrounding the SMBH. The disk produces most of the luminosity as optical and UV thermal continuum emission. This emission is also stochastically and continuously time variable, and despite decades of study of this phenomenon, we still do not fully understand what drives the variability.In the first part of my thesis, I introduce a new method of understanding and analyzing this stochastic variability. By assuming an axisymmetric accretion disk with a radial temperature profile, I use well-sampled multi-band UV/optical lightcurves to create "maps" of the accretion disk resolved in time and radius. The maps for a majority of the AGNs modeled are dominated by temperature fluctuations that move radially inwards and outwards slowly (relative to the speed of light). These structures challenge the current paradigm where accretion disk variability is dominated by processes like reverberation, as reverberation produces fluctuations that only move outwards at the speed of light.I spend the next part of my dissertation addressing transient variability in AGNs and around quiescent SMBHs. These include: changing-look events, where an AGN changes from one "type" to another over timescales of months to years; tidal disruption events (TDEs), where a star is ripped apart by the tidal forces of a SMBH and some of the debris rapidly accreted, producing a luminous transient; and ambiguous nuclear transients (ANTs), which are transients that possess peculiar qualities that overlap with both AGN flares and TDEs.Finally, I finish my dissertation addressing a different aspect of astronomical variability: dying massive stars. While seemingly unrelated, SMBHs may have started as the stellar-mass BHs formed after the core-collapse of a massive star. All massive stars die with an implosive core-collapse. The majority then explode violently as a luminous supernova (SN), but some fraction of them instead continue imploding and quietly disappear as a failed SN. I study both successful and failed SNe using data from the Large Binocular Telescope (LBT) Search for Failed SNe. I find a new candidate failed SN, update the fraction of failed SNe, and place upper limits on the pre-SN variability of the progenitor of SN 2023ixf, the closest SN in a decade.

Subject Added Entry-Topical Term  

Astronomy.

Subject Added Entry-Topical Term  

Astrophysics.

Subject Added Entry-Topical Term  

Physics.

Index Term-Uncontrolled  

Black holes

Index Term-Uncontrolled  

Active galactic nucleus

Index Term-Uncontrolled  

Accretion disk

Index Term-Uncontrolled  

Astrophysical processes

Added Entry-Corporate Name  

The Ohio State University Astronomy

Host Item Entry  

Dissertations Abstracts International. 86-04B.

Electronic Location and Access  

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Control Number  

joongbu:655772