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On stochastic and transient variability around black holes*

Neustadt, Jack Madison Marshall
http://orcid.org/0000-0001-7351-2531
http://rave.ohiolink.edu/etdc/view?acc_num=osu1721060632310687

Abstract Details

2024, Doctor of Philosophy, Ohio State University, Astronomy.
Accretion 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.
Christopher Kochanek (Advisor)
Richard Pogge (Committee Member)
Krzysztof Stanek (Committee Member)
305 p.
Astronomy; Astrophysics; Physics
black holes; active galactic nucleus; active galactic nuclei; transients

Recommended Citations

Citations

  • Neustadt, J. M. M. (2024). On stochastic and transient variability around black holes* [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1721060632310687

    APA Style (7th edition)

  • Neustadt, Jack. On stochastic and transient variability around black holes*. 2024. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1721060632310687.

    MLA Style (8th edition)

  • Neustadt, Jack. "On stochastic and transient variability around black holes*." Doctoral dissertation, Ohio State University, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=osu1721060632310687

    Chicago Manual of Style (17th edition)

osu1721060632310687
57
© 2024, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.