Transcript Slide 1

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The Sun’s power output is 4 x 1026 watts
If the energy source was gravitational or chemical, the
Sun would have formed more recently or depleted its
fuel long ago.
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The Sun is powered by thermonuclear fusion reactions
in the core where hydrogen is being converted into
helium and releasing energy in a process called the
proton-proton chain.
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What is the energy source for the Sun?
Our model of the Sun’s interior must account for the
conditions we observe at the surface.
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• Our star appears to be static.
At extremely high temperatures and pressures, four
hydrogen atoms can combine to make one helium atom
and release energy.
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• The Sun consumes 6 x 1011 kg of hydrogen per second
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Hydrostatic equilibrium
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Interstellar Medium
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How is the energy transported in a star?
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What happens when the hydrogen runs out?
The interior can no longer repel the inward pull of
gravity.
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The core heats under pressure, causing the outer layers
to expand and swell.
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These outer layers get farther from the hot core and
cool, resulting in a red color.
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An aging star like the Sun may lose as much as
40% of its original mass.
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What happens to large stars at the end of their life?
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Iron is split into (p+, n, e-) by gamma rays
• p+ + e- → n
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