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Thomas A. Callister
Bachelor of Arts
Physics, Astrophysics, Gravitational-waves, Black holes, Binary black holes, Spin, Spinning black holes, LIGO, Laser Interferometer Graivational-wave Observatory, Compact objects, Data analysis, Bayesian inference, Hierarchical inference, General relativity
Black holes are some of the most mysterious and fascinating objects that exist: with a gravitational pull so strong that nothing, even light, can escape their clutches, they are sites of fundamentally-inaccessible regions of space-time. Despite this inaccessibility, black holes can be indirectly studied via the profound influence they have on their surroundings. Black holes in binary systems, for instance, are so massive and orbit each other with such great speeds that they emit observable gravitational waves (GW): ripples in the fabric of space-time. These GW signals contain a host of information about the astrophysical system that generated them, such as their masses and spins. The Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo detectors now regularly observe binary black hole (BBH) mergers, but the evolutionary origin of these events remains a mystery. Analysis of the distribution of spin across binary black hole systems may shed light on this mystery, offering a means of discriminating between different binary formation channels, such as field and dynamical evolution. In this thesis, using the data from Advanced LIGO and Virgo, I carefully characterize the distributions of the effective spin χeff and precessing spin χp of binary black holes, hierarchically measuring the distributions’ means and variances while accounting for selection effects and degeneracies between parameters. When using data from LIGO and Virgo’s first two observing runs (O1/O2), I find that the known population of binary black holes have χeff values that are both small and narrowly distributed, with both the distribution’s mean and variance consistent with zero at 95% credibility. These results are consistent with both field and dynamical binary formation channels, amongst others. I then explore the implications of these ensemble properties on individual BBH mergers, re-analyzing existing LIGO GW events under populationinformed spin priors. I find that uninformed spin priors yield overestimates of the effective spin magnitude of compact binary mergers, which is mitigated by using my populationinformed analysis. When incorporating novel data from LIGO and Virgo’s third observing run (O3a), I find several important changes from the O1/O2 analysis. First, the variance of the χeff distribution is no longer consistent with zero. Second, I discover two new phenomena: there exist BBH with negative χeff, and there there exists spin precession in the BBH population. For the first time, I find evidence for dynamical formation on a population level
©2020 Simona Jane Miller. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.
Miller, Simona Jane, "Using gravitational-wave signals to model the distribution of spin across the binary black hole population" (2020). Honors Project, Smith College, Northampton, MA.
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