- #1

wangyi

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As we know,

First, in the Swartzchild solution of GR, an observer outside the black hole will find it takes infinity time for any object to fall into the black hole.

Second, a black hole is formed by a star falling to its center.

Now the question arises: when a star is falling, and nearly to form a black hole, say, if one little piece of matter falls onto the star, it forms a black hole. At this time, the time for a observer to see the last matter falling onto the star is nearly infinate, that means no matter how long a period of time T given, we will find a piece of matter small enough which falls onto the star taking longer time than T according to the observer outside. Then how can a black hole form?

I have been confused about it for long. Thank you.