Curiosity☉ Sun
If 3He(3He,2p)4He were twice as fast, this model of the Sun's centre would give off about a fifth fewer boron‑8 neutrinos (−21%).
- Energy output −6%; the first 1% of the hydrogen burns 8% later.
Two helium‑3 nuclei fusing directly skip beryllium‑7, so fewer boron‑8 neutrinos reach Earth.
One-zone model at 16 MK over 1 billion years. Real stars adjust. The neutrinos are those of this gas at the model's temperature: a real star would adjust its temperature to keep its luminosity. Doubling is a what-if, not the rate's actual uncertainty. How well this rate is known: well known.