First detection of ringing of newborn black hole: Testing the no-hair theorem

It all began with Astronomer John Wheeler, who coined the term "black hole" nearly 50 years ago, and who famously said that "black holes have no hair" because of their simplicity.

"Hair" is used as a colloquial term among physicists as a stand-in for any other measure needed to describe a black hole, apart from the traditional three-quantity model: mass, angular momentum (how fast they spin) and electrical charge.