After two neutron stars collided and formed a black hole, scientists noticed an echo resulting from the gravitational waves formed by the collision of the two stars. Scientists believe this echo is the result of the gravitational waves bouncing off a physical boundary located between what’s called the event horizon (previously thought to have no physical characteristics) and the photon sphere. Some scientists now think that the event horizon may have some physical characteristics and a quantum side. This isn’t yet confirmed, but if true, this would be a huge step towards better understanding how black holes work and the relationship between quantum physics and relativity. I’m sure I’m not explaining this perfectly, so make sure to read the article!