Given that time slows to a stand-still at the event horizon of a Black Hole, how long would it take a black hole to form, from the perspective of an outside observer?

It would seem, as a massive star collapses into a Black Hole, time on the surface of the star would slow as the gravity on the surface reaches the level of a black hole. Within the collapsing star, gravity is less and time continues closer to normal speed. Looking at it from the outside, far away, the black hole never quite forms. As it would take an infinite amount of time.

Any thoughts on this?


marked as duplicate by Qmechanic Feb 5 '18 at 14:35

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  • $\begingroup$ Time in the black hole doesn't slow down - fundamental processes do. For example, nuclear fusion would almost cease at the surface of the hard core of the black hole, as would thermal radiation. For the outside observer, the black hole simply forms at the expected pace. For a (wholly hypothetical) human stood on the surface of the hard core, eons would pass by between each blink of the eye that they could muster - although of course in practice they'd be busy getting buried beneath the surface under a torrent of incoming matter, and crushed into oil and gas. $\endgroup$ – Steve Feb 5 '18 at 14:28