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Abstract

Omega Centauri (ω Cen) is the most massive globular cluster of the Milky Way. Due to its complex stellar populations, it is believed to be the stripped nucleus of an accreted dwarf galaxy, making it not only an important witness of the Milky Way’s merger history but also the closest galactic nucleus to us on Earth. Many of its properties are still under active investigation, including the origin and kinematics of its multiple stellar populations, the mass distribution in its center, and the potential connection with the debris of its former host galaxy. As a stripped nucleus, ω Cen has also been a candidate for hosting an intermediate-mass black hole, but previous searches have remained inconclusive. In this thesis, I present a novel, comprehensive astrometric and photometric catalog based on 20 years of archival and new Hubble Space Telescope observations. The underlying dataset contains over 800 individual images and allows for the measurement of precise proper motions for around 1.4 million stars within the half-light radius (r_HL=5’) of ω Cen. Within the new dataset, I discovered 7 fast-moving stars within a radius of just 3 arcseconds (0.1pc) around the cluster center. These stars move faster than the expected local escape velocity, and their presence can be best explained by being bound to a black hole with a mass of at least 8200 solar masses. These results make a strong case for ω Cen hosting an intermediate-mass black hole, a long-sought missing link between stellar mass and supermassive black holes. To study the overall kinematics of ω Cen, I combined the astrometric dataset with a recent spectroscopic catalog, allowing the determination of the full 3-dimensional velocity vector for thousands of stars. This analysis provides improved measurements of the velocity dispersion profile, the rotation curve, and the state of energy equipartition of ω Cen. By combining proper motions with line-of-sight velocities, I calculated an improved kinematic distance estimate of (5445±41) pc, the most precise distance to ω Cen available. In the final scientific chapter, I present preparatory efforts for the guiding system of the new SDSS-V Local Volume Mapper (LVM). This novel wide-field integral field spectrograph celebrated its first light in 2023. While the primary goal of this instrument is to map interstellar gas within the Milky Way and the Magellanic Clouds, it can also study the integrated light of star clusters such as ω Cen, benchmarking unresolved extragalactic studies. I present preliminary results of the overall line-of-sight kinematics measured with the LVM, which agree with our resolved results. The results of this thesis are an important step towards a better understanding of the formation history of ω Cen and low mass galactic nuclei in general. The large astro-photometric catalog is already being used for detailed studies of the age-metallicity relation, the abundances, and the subpopulations of ω Cen. The precise kinematic measurements will be followed-up with detailed dynamical models. Finally, the detection of fast-moving stars marks a breakthrough in the search for local intermediate-mass black holes in star clusters and can serve as a blueprint for future searches in other clusters, although new instrumentation such as ELT MICADO will be required.