Objects collapsing to black holes

  • #1

Main Question or Discussion Point

Im going to keep this very concise, mainly because i vaguely understand what I am discussing but anyways, as most informed people are aware black holes have an infinitely strong pull at their singularity and can even inhibit light.
I am curious as towards the actual phenomena or reasons how an object with finite density could generate endless energy. Does it just contract until it makes a fold in spacetime?

To expatiate on that, what is the circumference or the pinnacle distance of gravitational effects emitted from the black hole if any. input would be very appreciated
 

Answers and Replies

  • #2
Nabeshin
Science Advisor
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I am curious as towards the actual phenomena or reasons how an object with finite density could generate endless energy. Does it just contract until it makes a fold in spacetime?
To speak of the density of a black hole is to invite confusion. Really, there are two routes one can go for discussing the density of such an object.

1. The mathematical route. As I described in a recent thread, a black hole is really a solution to Einstein's equations with a delta-function mass distribution -- that is, a point particle. Since points occupy zero volume, their density is infinite. This is perhaps the more correct of the two approaches, but it gives us very little information so most of the time we opt for the second result:

2. The pragmatic. A black hole is defined best by a single length scale: the size of its event horizon. I'm sure you know about event horizons, but it bears repeating that there is nothing pathological or physical about the horizon itself -- it is a mathematical boundary in spacetime. So usually when we talk about density we divide the total mass of the hole by the volume enclosed by the event horizon, thus yielding a finite number. And indeed, this density can actually be made arbitrarily small by increasing the mass of the hole!

As far as the endless energy part, I'm not entirely sure what you mean by this. What makes you say a black hole is capable of supplying an infinite amount of energy? Certainly, a finite amount of energy goes into creating the object!
 
  • #3
Chronos
Science Advisor
Gold Member
11,408
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Singularities are mathematical artifacts, IMO. Infinite density is not required to generate an event horizon.
 
  • #4
thanks
 

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