Trialpha: Hoyle State
Cosmology & the Sky arc, page 147 of 193. Back to The Pixelated Physics Universe
Who they are
Trialpha juggles three helium nuclei inside a star. For a moment they become carbon, and that is why you exist.
Trialpha is a character of the Cosmology & the Sky arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
In 1953 Fred Hoyle predicted a carbon level near 7.7 MeV; a Caltech team measured 7.68 ± 0.03 MeV, and Cook, Fowler and Lauritsen assigned it 0⁺ in 1957.
$$ \begin{gathered} {}^{4}\mathrm{He} + {}^{4}\mathrm{He} \rightleftharpoons {}^{8}\mathrm{Be}, \qquad {}^{8}\mathrm{Be} + {}^{4}\mathrm{He} \to {}^{12}\mathrm{C}^{*}\,(7.654\ \mathrm{MeV},\ 0^{+}) \\ {}^{12}\mathrm{C}^{*} \to {}^{12}\mathrm{C} + \gamma\gamma \quad (\text{rarely; usually } {}^{12}\mathrm{C}^{*} \to 3\,{}^{4}\mathrm{He}) \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| ${}^{4}\mathrm{He}$ | helium-4 nucleus (alpha particle) | 1 |
| ${}^{8}\mathrm{Be}$ | beryllium-8, unstable, lives about 10⁻¹⁶ s | 1 |
| ${}^{12}\mathrm{C}^{*}$ | carbon-12 in its excited Hoyle state | 1 |
| $\mathrm{MeV}$ | mega-electronvolt, 1.602 176 634 × 10⁻¹³ J (exact) | J |
| $0^{+}$ | spin 0, positive parity | 1 |
| $\gamma$ | gamma-ray photon | 1 |
Sources
- Hoyle (1954) On Nuclear Reactions Occurring in Very Hot Stars. I., Astrophys. J. Suppl. 1, 121
- Dunbar, Pixley, Wenzel & Whaling (1953) The 7.68-MeV State in C12, Phys. Rev. 92, 649
- Cook, Fowler, Lauritsen & Lauritsen (1957) B12, C12, and the Red Giants, Phys. Rev. 107, 508
Crossovers
Trialpha meets Trimera (Efimov States). Trialpha binds three alpha particles into carbon's Hoyle state. Trimera binds three atoms into Efimov states. Both are three-body quantum problems, but the Hoyle state is a single nuclear resonance, not an Efimov tower.
Trialpha meets Kilonova (GW170817 Neutron Star Merger). Trialpha makes carbon in stars. Kilonova shows where much heavier elements come from: a neutron-star merger whose glow showed the signature of rapid neutron capture. Different furnaces build different parts of the periodic table.
Trialpha meets Gamowyn (Narrow Window). Gamowyn's window lets helium nuclei fuse in a red giant's core. Trialpha's Hoyle state makes the third helium nucleus stick, so carbon forms quickly enough.
Wear the lore
- Trialpha – The Hoyle State Physics T-Shirt
- Related infographic poster: The HR Diagram as a Kingdom – Plate 066 Physics Poster
Concept keywords: Hoyle State, Trialpha, Cosmology & the Sky, physics lore, Pixelated Physics