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Graduation Term
Spring 2025
Degree Name
Master of Science (MS)
Committee Chair
Matthew Caplan
Committee Member
Daniel Holland
Committee Member
Neil Christensen
Abstract
Presently, primordial black holes (PBHs) in the asteroid-mass window from 10−16 M⊙ to 10−10 M⊙ are a popular dark matter candidate. If they exist, some stars would capture them upon formation, and they would slowly accrete the star over gigayears. Such Hawking stars – stars with a central PBH – provide a novel channel for the formation of both sub-Chandrasekhar mass black holes as well as red straggler stars. Here we report on stellar evolution models that extend our previous work to Hawking stars with masses between 0.5 and 1.4 M⊙. We explore three accretion schemes, and find that a wide range of PBHs in the asteroid-mass window can robustly accrete stars as small as 1 M⊙ within the age of the Universe. This mechanism of producing sub-solar mass black holes is highly dependent on the assumed accretion physics and stellar metallicity. Lower-metallicity stars are generally accreted more rapidly, suggesting that it may be more likely for sub-Chandrasekhar mass Hawking stars formed in the early universe, such as those in ultra-faint dwarf (UFD) galaxies, to transmute their star into a sub-Chandrasekhar mass black hole within a Hubble time. We present a stellar population synthesis of a Draco II-like UFD galaxy containing Hawking stars and show that the number of red stragglers they produce can qualitatively match the observed population for black hole seed masses around 10−11 M⊙ and under the assumption that they accrete with high radiative efficiency.
Supermassive black hole (SMBH) formation remains as an unsolved problem. Quasi-stars represent a newer but still viable channel that have been explored more in depth in recent years. This mechanism predicts that the seeds of SMBHs form from the monolithic gravitational collapse of massive low-metallicity gas clouds in the cores of proto-galaxies that then grow by accreting a gaseous envelope as a quasi-star. In this work, we expand and modify the aforementioned techniques for Hawking stars in Mesa in order to model these quasi-stars. In addition, we implement updated boundary conditions and wind-schemes by which we can further understand the structure, evolution, and stability of quasi-stars.
Access Type
Thesis-ISU Access Only
Recommended Citation
Santarelli, Andrew D., "Stellar Evolution Modeling of Exotic Stars with Central Black Holes" (2025). Theses and Dissertations. 2120.
https://ir.library.illinoisstate.edu/etd/2120
