Interesting reading! But I take issue with the title. The article says

   "Laser Interferometer Gravitational Waves Observatory" (LIGO) in the USA, are able to detect these waves.

So not unseen, in as they've been seen :)

Curiously, its the fact that there was no visible light, that suggests it was this particular collision. Vs two black holes or two neutron stars. So I guess an indirect observation. Boy are astrophysicists clever!