Astro2020 Science White Paper Mapping the Inner Structure of Quasars with Time-Domain Spectroscopy Thematic Areas:  Planetary Systems  Star and Planet Formation ⊠ Formation and Evolution of Compact Objects  Cosmology and Fundamental Physics  Stars and Stellar Evolution  Resolved Stellar Populations and their Environments ⊠ Galaxy Evolution  Multi-Messenger Astronomy and Astrophysics Principal Author: Name: Yue Shen Institution: University of Illinois at Urbana-Champaign Email: shenyue@illinois.edu Phone: 217-265-4072 Co-authors: (names and institutions) Scott Anderson, University of Washington, USA Edo Berger, Harvard-Smithsonian Center for Astrophysics, USA W.N. Brandt, The Pennsylvania State University, USA Gisella De Rosa, Space Telescope Science Institute, USA Xiaohui Fan, University of Arizona, USA Laura Ferrarese, National Research Council of Canada, Canada Suvi Gezari, University of Maryland, USA Matthew Graham, California Institute of Technology, USA Jenny Greene, Princeton University, USA Catherine J. Grier, University of Arizona, USA Josh Grindlay, Harvard University, USA Daryl Haggard, McGill University, Canada Patrick B. Hall, York University, Canada Luis Ho, Kavli Institute for Astronomy and Astrophysics, Peking University, China Hector Ibarra Medel, University of Illinois at Urbana-Champaign, USA Dragana Ilic, University of Belgrade, Serbia Zeljko Ivezic, University of Washington, USA Jacob Jencson, California Institute of Technology, USA Linhua Jiang, Kavli Institute for Astronomy and Astrophysics, Peking University, China St´ ephanie Juneau, National Optical Astronomy Observatory, USA Mansi Kasliwal, California Institute of Technology, USA Juna Kollmeier, Carnegie Observatories, USA Alexander Kutyrev, NASA/GSFC, USA Jennifer I-Hsiu Li, University of Illinois at Urbana-Champaign, USA Guilin Liu, University of Science and Technology of China, China 1 arXiv:1903.04533v1 [astro-ph.GA] 11 Mar 2019