Overview
This lecture explains how the Sun fuses hydrogen atoms to form helium, the products and consequences of this process, and how we detect evidence for solar fusion.
Fusion in the Sun
- The Sun fuses four hydrogen atoms to produce one helium atom in its core.
- This process is called nuclear fusion and is the source of the Sun’s energy.
- Helium can be identified by its two protons in the nucleus.
Fusion Formula & Products
- The simplified fusion reaction is: 4 Hydrogen atoms → 1 Helium atom + 2 neutrinos + 6 gamma rays.
- Neutrinos (represented by the Greek letter ν, pronounced "nu") are nearly massless, neutral particles.
- Gamma rays are high-energy photons produced in the core.
- Positrons and electrons produced in intermediate steps do not survive the process.
Effects of Fusion
- The number of atoms in the Sun’s core decreases over time as hydrogen is fused into helium.
- The gradual depletion of hydrogen will eventually cause the Sun to run out of fuel and stop shining, in about 6-7 billion years.
Light from the Sun
- Although fusion primarily produces gamma rays, the main light emitted from the Sun’s surface is visible and ultraviolet (UV) light.
- Gamma rays are transformed into visible and UV light as they travel from the core to the surface.
Evidence for Fusion: Neutrinos
- We cannot directly see the Sun's core, but we know fusion occurs there because of the detection of solar neutrinos.
- Neutrinos pass through matter almost unaffected, escaping the Sun immediately after being produced.
- Specialized underground detectors are used to observe solar neutrinos on Earth.
- Billions of solar neutrinos pass through every person every second, both day and night.
- Neutrinos rarely interact with matter and generally travel through space indefinitely.
Key Terms & Definitions
- Nuclear Fusion — the process of combining lighter atomic nuclei (like hydrogen) to form a heavier nucleus (like helium), releasing energy.
- Neutrino — a neutral, nearly massless subatomic particle produced in nuclear reactions, symbolized by the Greek letter ν.
- Gamma Ray — high-energy electromagnetic radiation emitted during nuclear reactions in the Sun's core.
Action Items / Next Steps
- Review the fusion formula and understand each product listed.
- Check Discord for the posted diagram of the fusion process.