More like this "... an afterglow in gamma rays and the optical, occurring about 19 hours after-the-fact" I know that 19 hours is like a blink in cosmic terms, but just wondering... if both EM waves and grav. waves propagate at the same speed, why a delay of 19 hours? Given the violent nature of the event.. one would guess that gamma rays where being produced during the merger, at the exact moment of it... but 19 hours after it... maybe not from the event as such but from BH feeding on the material that is nearby? By Sinisa Lazarek (not verified) on 08 Jun 2017 #permalink