We analyze Chandra X-ray Observatory imaging of 108 galaxies hosting nuclear star clusters (NSCs) to search for signatures of massive black holes (BHs). NSCs are extremely dense stellar environments with conditions that can theoretically facilitate massive BH formation. Recent work by Stone et al. (2017) finds that sufficiently dense NSCs should be unstable to the runaway growth of a stellar mass BH into a massive BH via tidal captures. Furthermore, there is a velocity dispersion threshold ($40\;\rm{km\;s^{-1}}$) above which NSCs should inevitably form a massive BH. To provide an observational test of these theories, we measure X-ray emission from NSCs and compare to the measured velocity dispersion and tidal capture runaway timescale. We find that NSCs above the $40\;\rm{km\;s^{-1}}$ threshold are X-ray detected at roughly twice the rate of those below (after accounting for contamination from X-ray binaries). These results are consistent with a scenario in which dense, high-velocity NSCs can form massive BHs, providing a formation pathway that does not rely on conditions found only at high redshift.
Alpha clustering in warm and dense nuclear matter from heavy-ion collisions
Fudan University（复旦大学）；Shanghai Institute of Applied Physics, Chinese Academy of Sciences（中国科学院上海应用物理研究所）；Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Catania（意大利国家核物理研究所卡塔尼亚分部）；Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University（中山大学中法核工程与技术学院）；Shanghai Research Center for Theoretical Nuclear Physics, NSFC and Fudan University（国家自然科学基金委与复旦大学理论核物理上海研究中心）；School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院）；Cyclotron Institute and Department of Physics and Astronomy, Texas A&M University（德克萨斯农工大学回旋仪研究所及物理与天文系）
