0 Assigned ID: 3706 ----- Attempting Submission 1 (Fri Mar 25 23:26:01 GMT 2022) ----- Galactic nuclei have been proposed to produce the types of binary black hole mergers that have recently been detected by gravitational wave observatories. Tight black hole-star binary systems are likely precursors to these mergers. However, the number of tight black hole-star binaries in galactic nuclei is not yet well constrained. The Milky Way Galactic center, being the only Galactic nucleus with individually resolvable stars, allows constraining the presence of black hole-star binary systems in galactic nuclei and evaluating if they indeed are likely factories of binary black hole mergers observed with gravitational waves. We propose to use 9.7 years of archival HST-WFC3IR observations of the central 5 parsecs of the Galactic center to photometrically search for and characterize stellar-mass black holes in close binary systems. We will use the multi-epoch observations to search for variability consistent with ellipsoidal effects and Doppler beaming expected in close binary systems with compact components. Using preliminary simulations based on the binary fraction and stellar-mass black hole production rates for the young and old stellar populations of the Galactic center, we predict that our experiment should detect 1 to 6 close binary systems possesing stellar-mass black holes. In detected systems, we will model the flux variability to constrain compact object masses. Our proposed experiment can detect stellar-mass black holes in detached binary systems at the Galactic center, and constrain the viability of galactic nuclei to produce the recent binary black hole mergers observed by gravitational wave observatories. Our team consists of members who have deep experience with HST, the proposed photometric methods, and Galactic center science. Co-I Do has been PI of previous successful HST programs using WFC3-IR. Co-I Hosek has experience with astrometric projects using HST studying the Milky Way Nuclear Star Cluster and the Arches and Quintuplet clusters. PI Gautam has analyzed binary stars and variable stars at the Galactic center in ground-based photometric experiments. Scientifically, our entire team has long experience studying the Galactic center stellar populations. PI Gautam will lead the analysis proposed in the Analysis Plan to construct the individual frame stellar photometry catalog, search for candidate binary systems, and characterize detected candidates. Co-I Hosek will advise in the creation of the stellar photometry catalog and analysis. Co-I Sakai and Co-I Do will provide oversight on the project and consult on the analysis and scientific interpretations. All team members will participate in writing and publishing the results. For more details, please see our Analysis Plan. Stellar Populations and the Interstellar Medium Stellar Physics and Stellar Types 0 Regular false false false false false false SUPPORTED