OICC Press Journal of Theoretical and Applied Physics 2251-7235 20 4 2026 08 31 Observational Study of Supermassive Black Holes in Nearby Galaxies: Mass Distributions, Scaling Relations, and Environmental Effects from HST and JWST Data 10.57647/jtap.2026.2004.32 EN Mahgoub A. Salih Department of Physics, College of Science, Qassim University, Buraydah 51452, Saudi Arabia https://orcid.org/0000-0001-8652-9842 Journal Article 2026 08 31 We present a comprehensive study of supermassive black holes (SMBHs) in 82 nearby galaxies (\(D < 50\) Mpc) using archival Hubble Space Telescope (HST) and new James Webb Space Telescope (JWST) data. Combining high-resolution imaging, stellar kinematics, and infrared spectroscopy with four independent mass determination methods, we derive precise black hole masses spanning \(5 \times 10^4\) to \(7 \times 10^9\) \(M_{\odot}\) and uncover key insights into their formation and growth. Our findings include: 1. A robust intermediate-mass black hole (IMBH; \(10^{4.7}\)--\(10^{6.0}\) \(M_{\odot}\)) fraction of \(6 \pm 3\)% after completeness corrections, broadly consistent with a mixed formation scenario (\(\sim\)20% direct collapse, \(\sim\)80% stellar remnants, based on host-galaxy correlation analysis); 2. Systematic environmental mass enhancements following a clear hierarchy (\(\Delta \log M_{\mathrm{BH}} = 0.32 \pm 0.07\) dex in clusters, \(0.18 \pm 0.09\) dex in groups), driven by enhanced mergers, ram-pressure feeding, and preprocessing effects; 3. Detection of a hidden AGN population in 17 galaxies (21%) through JWST's enhanced spectroscopic capabilities, revealing coronal lines and hot dust signatures that imply duty cycles of \(\sim 10^{-2}\) for low-luminosity activity in massive galaxies; and 4. A three-parameter fundamental plane (\(M_{\mathrm{BH}} \propto \sigma_*^{3.82} \times M_{\mathrm{bulge}}^{0.31} \times R_{\mathrm{eff}}^{-0.15}\)) with scatter reduced to \(0.26 \pm 0.03\) dex, physically linking black hole mass to central binding energy and baryon concentration. These results, enabled by JWST's revolutionary infrared capabilities combined with HST's legacy archive, establish new benchmarks for SMBH demographics and provide stringent constraints on formation models, environmental growth mechanisms, and black hole-galaxy co-evolution. The study sets the foundation for next-generation surveys with Roman Space Telescope, ELTs, and multi-messenger astronomy with LISA gravitational wave detection.