Why don't stars explode? What holds them together?

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Discussion Overview

The discussion revolves around the mechanisms that prevent stars from exploding and the forces that hold them together, focusing on concepts of gravity, nuclear fusion, and pressure balance. Participants explore theoretical and conceptual aspects of stellar stability, with references to mathematical relationships and physical principles.

Discussion Character

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

Main Points Raised

  • Some participants express confusion about how gravity can hold together the immense mass of a star undergoing nuclear fusion, suggesting that outward pressure should dominate.
  • It is noted that only a small portion of a star's mass undergoes fusion at any given time, which contributes to the star's longevity.
  • Participants mention that the stability of a star is due to a balance between the outward pressure from nuclear fusion and the inward pull of gravity.
  • One participant proposes comparing the Sun's gravitational binding energy to its energy output from fusion to understand stability better.
  • There are discussions about the nature of nuclear fusion, with some participants clarifying that it converts hydrogen into helium rather than fusing them together.
  • Concerns are raised about the implications of energy loss and how it affects the balance of forces within a star.
  • Some participants discuss the role of pressure and electromagnetic forces in maintaining stellar stability, emphasizing the importance of temperature in this balance.
  • There are questions regarding the nature of forces produced by nuclear fusion and whether they can be considered repulsive.
  • One participant humorously notes a misunderstanding about the distance light travels in relation to the Sun's core and its surface.

Areas of Agreement / Disagreement

Participants express a range of views on the balance of forces in stars, with some agreeing on the general principle of equilibrium between gravity and pressure, while others raise questions and uncertainties about the specifics of these interactions. The discussion remains unresolved regarding the precise accounting of forces and the implications of energy dynamics.

Contextual Notes

Some participants reference mathematical relationships and concepts that may depend on specific definitions or assumptions about stellar physics. There are also unresolved points regarding the nature of nuclear fusion and its effects on stellar dynamics.

  • #31
rocketman7 said:
stars are in a state of hydrostatic equallibrium. outward radiative pressure from photons and nuetrinos emitted in he core are balanced by the inward force of gravity.:smile:

So are we stating that the inward force of gravity, squeeze's photons out from the inner core, similar, like a "wet sponge" expelling water when squeezed, so to speak?
 
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  • #32
rocketman7 said:
stars are in a state of hydrostatic equallibrium. outward radiative pressure from photons and nuetrinos emitted in he core are balanced by the inward force of gravity.:smile:

Photons are only the dominant source of pressure in stars much more massive than the sun. In most stars, it is the particles themselves that are doing the pushing, not the photons (and certainly not the neutrinos).
 
  • #33
rocketman7 said:
stars are in a state of hydrostatic equallibrium. outward radiative pressure from photons and nuetrinos emitted in he core are balanced by the inward force of gravity.:smile:


While this is technically true, as SpaceTiger pointed out, radiation pressure is insignificant in the case of the sun.

I whipped this up in Matlab real quick to demonstrate. The graph is on a log scale, so the 10^# you see on the y-axis is the same as that part in scientific notation. it had to be log scale for the gas pressure to even be noticeable on the graph. A difference of 10^4 is a factor of 10,000 difference between the two.
 

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