Slide 1
Pressure supports the Sun against inward gravity
The Sun is made mainly of hot plasma, gas containing charged particles. Gravity pulls inward. Pressure increasing toward the centre provides outward support.
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Plasma contains freely moving charged particles. The Sun’s visible surface is therefore not a solid crust: it is the layer from which much of the light we observe escapes.
Slide 2
Deeper pressure supports the material above
Pressure increases toward the solar interior. Each layer must support the weight of material farther out while responding to the gravity acting on it.
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The balance is called hydrostatic equilibrium. It describes opposing influences within the star, not an absence of motion in the material or an assertion that the Sun never changes.
Slide 3
Core fusion supplies energy to maintain the hot interior
Nuclear fusion in the core releases energy that eventually escapes from the surface. This energy source helps maintain the hot interior.
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Fusion is concentrated where temperature and density make reactions sufficiently likely. The visible surface is far cooler than the core, so observing sunlight does not mean looking directly at the reaction region.
Slide 4
Radiation and moving plasma carry energy outward
Radiation carries energy through much of the interior. In the outer convection zone, moving plasma also transports energy toward the surface.
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Convection involves warmer material rising and cooler material sinking. The pattern of granules visible on the Sun reflects this churning near the surface rather than a fixed arrangement of solid features.
Slide 5
Changing core conditions eventually change the star
The Sun’s present structure depends on its composition and energy production. Changes in the core eventually alter the balance and the star’s size.
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A stable star is not an object with an unlimited fuel supply. Stellar evolution studies how gradual internal changes lead to new structures even when the star appears nearly constant over a human lifetime.
Sources
- Sun Facts
NASA
- The Solar Interior: Theory
OpenStax, Rice University
- Layers of the Sun
NASA