Investigating a Changing-state Event in ZTF18abuamgo

Understanding the mechanisms behind rapid spectral transitions in Active Galactic Nuclei (AGN) remains a key challenge in extragalactic astrophysics. Changing-Look (CL) AGN — in which broad emission lines emerge or vanish on timescales of months to years — defy standard expectations based on the physical extent of the accretion disc and broad-line region (BLR) surrounding supermassive black holes (SMBHs). These transitions provide a rare window into accretion state changes in real time, particularly in systems with high or variable accretion rates. In this contribution, I present the "turn-on" transition of the CL AGN ZTF18abuamgo, monitored over four years with multi-epoch spectroscopy. I extract, for the first time, the physical properties of a rapidly evolving BLR in a CL source, enabled by the appearance of broad Hydrogen Balmer emission lines. I will also discuss how CL phenomena complicate single-epoch SMBH mass estimates, with implications for black hole scaling relations and the demographics of actively accreting SMBHs across cosmic time.