Star

:This article is about celestial bodies. {{otheruses}}

Nuclear fusion reaction pathways

A variety of different nuclear fusion reactions take place inside the cores of stars, depending upon their mass and composition (see Stellar nucleosynthesis).

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Stars begin as a cloud of mostly hydrogen with about 25% helium and heavier elements in smaller quantities. In the Sun, with a 107 K core, hydrogen fuses to form helium in the proton-proton chain:

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:41H → 22H + 2e+ + 2νe (4.0 MeV + 1.0 MeV)

Related Topics:
¹H - ²H - E⁺ - ν_e - EV

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:21H + 22H → 23He + 2γ (5.5 MeV)

Related Topics:
³He - γ

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:23He → 4He + 21H (12.9 MeV)

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These reactions result in the overall reaction:

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:41H → 4He + 2e+ + 2γ + 2νe (26.7 MeV)

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In more massive stars, helium is produced in a cycle of reactions catalyzed by carbon, the carbon-nitrogen-oxygen cycle.

Related Topics:
Catalyzed - Carbon - Carbon-nitrogen-oxygen cycle

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In stars with cores at 108 K and masses between 0.5 and 10 solar masses, helium can be transformed into carbon in the triple-alpha process:

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:4He + 4He + 92 keV → 8*Be

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:4He + 8*Be + 67 keV → 12*C

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:12*C → 12C + γ + 7.4 MeV

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For an overall reaction of:

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:34He → 12C + γ + 7.2 MeV

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