# A question about Snyder calculation of imploding stars(1939)

1. Nov 23, 2006

### Born2Perform

hi:
Using gr and with great idealizations he discovered that the surface of imploding stars, viewed by a static external observer, seems to freeze when its circumference nears the horizon circumference for that star.
If i am not wrong this was also confirmed by Wheeler's student Wakano several years after.

Probably i misunderstood something in those reports, but if not, how can we see black holes, if the surface takes an infinite amount of our time to cross the horizon? thank you

2. Nov 23, 2006

### pervect

Staff Emeritus
This is being discussed in several recent threads right now.

3. Nov 27, 2006

### Chris Hillman

Oppenheimer-Snyder model of gravitational collapse

Hi, Born2Perform,

2. Some verbal summaries of the OS model do attempt to describe some features of the OS model by saying something like "the surface of imploding stars, viewed by a static external observer, seems to freeze when its circumference nears $$r=2m$$". This is confusing and misleading on many different levels, and is almost universally deprecated by modern textbook authors, and even by those authors of popular books, such as Thorne, Wald, and Geroch, who also happen to be leading experts on gtr. For an excellent discussion of the physical interpretation of the OS collapsing dust ball model, try the classic textbook Gravitation, by Misner, Thorne, and Wheeler.