0 Assigned ID: 3093 ----- Attempting Submission 1 (Fri Mar 25 01:10:49 GMT 2022) ----- HST Phase I Proposal 3093 successfully submitted. Receipt: # 3093-1 ----- Attempting Submission 2 (Fri Mar 25 12:10:13 GMT 2022) ----- HST Phase I Proposal 3093 successfully submitted. Receipt: # 3093-2 ----- Attempting Submission 3 (Fri Mar 25 12:15:02 GMT 2022) ----- Massive star clusters are a primary candidate for hosting the binary black hole mergers observed using gravitational waves. This is due to theoretical expectations that massive clusters can retain large numbers of stellar mass black holes, which then sink to the center of the cluster and form a steady supply of binary systems. However, only a handful of black holes have been detected in clusters, and there is no direct evidence that clusters host large numbers of them in their cores. Omega Centauri is the most massive star cluster in the Milky Way and indirect dynamical evidence suggests it hosts tens of thousands of stellar mass black holes in its core. A recent paper has estimated that these black holes should create detectable microlensing events every 1-10 years. Here we propose a search for black hole microlensing events in Omega Cen using nearly 600 archival observations of the central regions of the cluster over the past 12 years. Based on existing rate estimates, which appear to be conservative, we expect to detect 1-2 black hole microlensing events. Thus, this proposal will likely result in the first black hole detected in Omega Cen and the first microlensing detection of a black hole in a star cluster. We will also improve theoretical rate estimatesto translate any detections (or a non-detection) into constraints on the total mass and radius of the stellar mass black holes in Omega Cen. Our team includes both theorists and observers with the wide range of expertise needed to carry out the project. Most of the observers (Seth, Neumayer, Haeberle, Libralalto, Bellini, Clontz, Kamann) are involved in an ongoing project to study the formation history of Omega Cen, including a recently completed MUSE proposal covering the entire region within the effective radius combined with a Cycle 29 HST program to measure proper motions beyond the core of the cluster also PI'ed by Anil Seth. More specifically, co-Is Haeberle, Neumayer, Libralalto, and Bellini have been workinfg over the past >1 year to derive the photometry and proper motions for the central HST archival data set on Omega Cen that is the focus of this proposal. This is an update of the work done in Bellini et al. 2017 and leverages co-I Bellini's expertise in this area. This work is being led by co-I Haeberle and is not being funded with NASA or HST funds. PI Seth and co-I Neumayer are also experienced in doing dynamical modeling similar to what is proposed to be done in the final part of this project. Co-Is Neumayer and Kamann are experts on MUSE spectroscopy which will be used to verify candidates. Co-I Strader is an expert on multi-wavelength populations of compact objects in clusters, and also has proprietary access to SOAR spectra if we are not able to get MUSE spectra or need time series spectroscopy. On the theory side, co-Is Veske and Zaris are the primary authors on the event rate predictions in Omega Cen and will help revise their estimates using a more realistic population of black holes. Co-I Rodriguez is an expert on BH binary mergers and performing Cluster Monte Carlo simulations. His existing simulations of very massive clusters (e.g. Rodriguez et al. 2020) will be the basis for creating more realistic radial profiles of the BH subsystems in clusters. Stellar Populations and the Interstellar Medium Stellar Physics and Stellar Types 0 Regular false false false false false false SUPPORTED