Black Holes: Mass, Schwarzschild Radius & Size

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Discussion Overview

The discussion revolves around the nature of black holes, specifically addressing their size, the concept of the Schwarzschild radius, and the implications of singularities. Participants explore theoretical aspects, definitions, and the complexities involved in understanding black holes within the frameworks of general relativity and quantum theory.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether a black hole, defined as a collapsed stellar structure, has no size but is characterized by its mass and Schwarzschild radius.
  • Another participant asserts that the size of a black hole is defined by its event horizon, noting that the actual volume is complicated by spacetime curvature, and suggests that a singularity, if it exists, would have no size.
  • A different contribution highlights that current physical theories struggle to describe conditions inside the event horizon, as quantum theory and general relativity do not align well.
  • One participant clarifies that the term 'black hole' encompasses the entire volume within the event horizon, which can have measurable properties like radius and surface area, and describes the geometric nature of non-rotating and rotating black holes.
  • Another participant elaborates on the nature of singularities in different types of black holes, stating that while a Schwarzschild singularity is a mathematical point, Kerr and Newman singularities are one-dimensional with defined circumferences and radii.
  • A later reply questions the concept of a one-dimensional singularity having a circumference and radius, prompting a discussion about dimensionality.

Areas of Agreement / Disagreement

Participants express differing views on the nature of black holes, particularly regarding the definition of size and the characteristics of singularities. There is no consensus on these points, and the discussion remains unresolved.

Contextual Notes

Participants acknowledge limitations in current theoretical frameworks and the complexities introduced by spacetime curvature and the interplay between quantum mechanics and general relativity.

goldsax
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If a black hole is a stellar structure that has collapsed on itself to a singularity does that mean it has no size? But is so defined by its mass and schwarzschild radius?
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The black hole has a size defined by the event horizon. The actual volume and such is a bit more complicated to determine due to spacetime curvature I believe. A singularity, IF it exists at all, would have no size.
 
Current physical theory is unable to accurately describe what is going on inside the event horizon of a black hole. Quantum theory and general relativity don't mesh, and they both come into play.
 
The thing to realize is that the term 'black hole' doesn't mean: 'the bit at the center where all of the mass is concentrated, that may or may not be a singularity'.

'black hole' refers to the whole volume inside the event horizon, which clearly can have a radius, surface area and volume.

my understanding is that non-rotating black holes are perfect spheres with a radii equal to their Schwarzschild radius, and that rotating black holes are distorted into oblate spheroids, as are most rotating stellar objects.
 
Drakkith said:
The black hole has a size defined by the event horizon. The actual volume and such is a bit more complicated to determine due to spacetime curvature I believe. A singularity, IF it exists at all, would have no size.

A Schwarzschild black hole singularity is a mathematical point, yes, and so is a Nordström black hole singularity. But Kerr and Newman black hole singularities are one dimensional - they have no thickness, but they have circumference, radius etc.
 
How can it be one dimensional with a circumference and a radius? does that make it 2 dimensional?
 

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