Wait, why would LIGO be ale to detect anything about the inside of merging black holes? Mass, angular velocity, and charge are aggregate properties of the whole

Wait, why would LIGO be ale to detect anything about the inside of merging black holes? Mass, angular velocity, and charge are aggregate properties of the whole black hole and detectable, but information about matter that has entered the event horizon is still hidden from us even with gravitational wave detection. If LIGO is able to retrieve information from the insides of black holes that should be earth-shattering news, no?