If an object emitting light falls into a black hole, the conventional wisdom is that an observer (at infinity) will never actually see it fall in - they will see it moving slower and slower as it approaches the horizon and then eventually freeze at the horizon, making the time of "falling in" to be infinite for the outside observer.

During BH mergers we can actually see one BH "fall into" another one in a finite time. Why does the same thing not happen with gravitational waves?

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    $\begingroup$ You are asking why gravitational waves are not doppler-shifted to infinity? This might have to do with the understanting of where the gravitational waves are been generated (in my uneducated opinion: they are not being generated in the event horizon of either of the black holes but in the surrounding space of the binary system). $\endgroup$
    – Swike
    Dec 7, 2019 at 18:56


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