Boundary of a black hole (5,7)

I believe the answer is:

event horizon

(Other definitions for event horizon that I've seen before include "(In astronomy) boundary of a black hole - no Heinz voter (anag)" , "(In astronomy) notional boundary of a black hole - viz not hereon (anag)" , "black hole terminates here" , "Point of no return" .)

I've seen this clue in the LA Times.

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