Star collapses to a singularity or is collapsing into singularity?

Question

This has bothered me for a while now, however I barely have a vocabulary to ask it. Please let me try.

When a star, at the end of its life starts to collapse into the black hole, all the atomic forces are overcome and the matter begins compresses to an increasingly small volume. Popular literature describes it as a collapse to an infinitely small point of infinite density.

I am imagining this process, the matter keeps compressing itself getting smaller and denser. The density is so great, relativistic effects become noticeable at first and then considerable as the density increases, for the outside observer the speed at which the matter collapses should appear to be lower, the closer we are to the center. We cannot observe it per se beyond the event horizont, but this is what we would expect right?

And this is where my image freezes, if this idea is taken to its limit, the star cannot collapse to a point, as long as there is an outside observer. The matter can at the closest be infinitesmally short distance from the center point but not quite reaching it.

Am I thinking about this right? Or is this nonsense? Why?

Answer 1

Your line of thinking is not nonsense, but it isn’t exactly right either.

The part that is not nonsense is that it is true that an observer outside the event horizon will never receive a signal from anything that happens inside the horizon.

The part that is not right is the idea that this would prevent the collapse. Causes, by definition, occur before effects. An observer receiving a signal from some event cannot cause that event because the signal reception occurs after that event. Similarly, failing to receive a signal cannot prevent the event from occurring.

Answer 2

Clarifying this point.

the star cannot collapse to a point, as long as there is an outside observer.

Dale has answered the "as long as there is an outside observer" , that cause and effect do not allow this.

About collapsing to a point. All classical theories predict mathematical singularities , think all the 1/r formulas that are so successful in modeling fields and classical interactions. At r=o they blow up. That is why quantum mechanics was necessary, with its probability distributions it makes a fuzzy point of the singularity. If you are interested see my answer here for the cosmological model.

Answer 3

From the point of view of the collapsing matter, it happens right away. It doesn't care if anyone is there to observe it, and you're not thinking of observation in the right way. Observation means any interaction with anything in this universe. Because of gravitational time dilation, we see it happen more and more slowly but it does happen. Like I said, if you were the star collapsing, it would seem instantaneous.