Actually, the     no-hair theorem (i.e., John A. Wheeler's (1911--2008) "black holes have no hair" rule) has been challenged since mid-2012 by black hole firewall paradox and other problems with understanding the event horizon (see, e.g., Black Hole Firewalls Confound Theoretical Physicists, Jennifer Ouellete, 2012; Information Preservation and Weather Forecasting for Black Holes, Stephen Hawking, 2014; Black Holes, Firewalls and Chaos from Gravitational Collapse, Pankaj S. Joshi & Ramesh Narayan, 2014).

    It is hard to discuss these arcane problems with our concept of the event horizon.

    They are tricky and yours truly is ignorant and there are NO generally accepted solutions.

    But event horizon problems imply black holes may NOT be nearly as simple people once thought when the no-hair theorem ruled supreme. In fact, now there is a yes-hair theorem (2022) (see also Pallab Ghosh, BBC, 2022), but even if this is confirmed, the no-hair theorem is probably approximately true at least effectively.

    To avoid difficult subjects, we will largely skirt the event horizon problems, but NOT forget them entirely.

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