Can black holes fully merge, according to a distant observer?

Question

According to a distant observer, an object falling into a black hole doesn't disappear behind the even horizon but rather red-shift due to time dilation.

Does the same apply to merging black holes? Does their mutual approach increasingly slows down, according to a distant observer, so that they don't fully merge in finite time?

Answer 1

Black hole forms once there is sufficient mass in a volume of space. Once you get close enough to a black hole according to distant observer, it's event horizon will expand and swallow you before you cross the previous event horizon. With you close enough there is now enough mass for a larger volume of space.