Observational strong gravity and quantum black hole structure
  Quantum considerations have led many theorists to believe that classical black hole physics is modified not just deep inside black holes but at {\it horizon scales}, or even further outward. The near-horizon regime has just begun to be observationally probed for astrophysical black holes -- both by LIGO, and by the Event Horizon Telescope. This suggests exciting prospects for observational constraints on or discovery of new quantum black hole structure. This paper overviews arguments for certain such structure and these prospects. 
Steven B. Giddings
gr-qc hep-th