Element forgeswhere gold and iron were made
Which elements come from the Big Bang, stars, supernovae and neutron star mergers? This page lists each element's origin by forge, with the key research.
Gold was not formed on Earth, and neither was iron. The game's element table sorts elements into eight kinds of origin, the eight "forges": the Big Bang, cosmic rays, low-mass stars, massive stars, white dwarf explosions, neutron star mergers, radioactive decay and artificial synthesis. This page lists which elements each forge made, then covers a few key studies behind them.
The eight forges
| Forge | Number of elements | Main examples |
|---|---|---|
| Big Bang nucleosynthesis | 3 | Hydrogen, helium, lithium |
| Cosmic-ray spallation | 2 | Beryllium, boron |
| Low-mass stars (slow neutron-capture process) | 24 | Carbon, nitrogen, fluorine, rubidium, strontium, yttrium, zirconium, niobium, molybdenum, cadmium, indium, tin |
| Massive stars (core-collapse supernovae) | 22 | Oxygen, neon, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, argon, potassium, calcium |
| White dwarf explosions (Type Ia supernovae) | 6 | Vanadium, chromium, manganese, iron, cobalt, nickel |
| Neutron star mergers (rapid neutron-capture process) | 26 | Ruthenium, rhodium, palladium, silver, antimony, tellurium, iodine, xenon, cesium, samarium, europium, gadolinium |
| Radioactive decay of uranium and thorium | 7 | Polonium, astatine, radon, francium, radium, actinium, protactinium |
| Artificial synthesis | 28 | Technetium, promethium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium |
In this table, artificial synthesis (28 elements) and neutron star mergers (26) have the most elements, and cosmic-ray spallation (2) the fewest. "Mainly from here in the game's element table" means this is the game's classification of each element's main source. An element may have more than one source.
How to read the table
The pattern in the table is clear. The long run of oxygen, neon, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, argon, potassium and calcium goes to the core-collapse supernovae of massive stars. The six elements vanadium, chromium, manganese, iron, cobalt and nickel go to white dwarf explosions. From ruthenium, rhodium, palladium and silver through to iodine, xenon, cesium, europium and gadolinium, the source is neutron star mergers. Carbon, nitrogen and fluorine go to low-mass stars. In other words, elements that sit next to each other on the periodic table often come from completely different objects. The game uses this sorting to show that every element on the periodic table has a specific "birthplace", and each birthplace ties to a study in the sections below, from Big Bang calculations to the energy source of stars to observations of neutron star mergers.
The lightest three: the Big Bang
Ralph Alpher and George Gamow were the first to calculate how light elements formed in the Big Bang. Hans Bethe's name was added to make the joke "αβγ". The paper is titled "The origin of chemical elements" (Alpher, Bethe and Gamow, Physical Review, 1948). Hydrogen, helium and lithium are the only members of this group.
The furnaces inside stars
How can the Sun burn for billions of years? Bethe worked out that stars shine by nuclear fusion, which solved the puzzle (Bethe, Physical Review, 1939). For stars to make enough carbon, Fred Hoyle predicted that carbon-12 must have a special energy level, which experiments soon confirmed (Hoyle, The Astrophysical Journal Supplement, 1954). A few years later, a hundred-page paper explained systematically how stars forge the elements of the periodic table step by step: "we are all star dust, starting here" (Burbidge, Burbidge, Fowler and Hoyle, Reviews of Modern Physics, 1957).
White dwarf explosions and iron
Iron, cobalt, nickel and the rest of the "iron group" are assigned mainly to white dwarf explosions in the table. White dwarfs have a mass limit of about 1.4 solar masses, and beyond it a star is bound to keep collapsing (Chandrasekhar, The Astrophysical Journal, 1931).
Neutron star mergers: the story of gold
The first time a single cosmic event was both "heard" and "seen": the merger of two neutron stars (Abbott et al., Physical Review Letters, 2017). The matter thrown out by the merger contains large amounts of heavy elements, and the gold in your ring most likely came from a collision like this (Kasen et al., Nature, 2017).
Radioactivity and artificial synthesis
The decay chains of uranium and thorium produce seven elements: polonium, astatine, radon, francium, radium, actinium and protactinium. Artificial synthesis supplies the most: from technetium and promethium to neptunium, plutonium and americium, and on to einsteinium, fermium, mendelevium and nobelium. One more detail from the game is worth adding: einsteinium and fermium were both discovered in the debris of the first hydrogen bomb test.
Want the originals? Search for these titles
- Alpher et al. (1948): "The origin of chemical elements"
- Bethe (1939): "Energy production in stars"
- Hoyle (1954): "On nuclear reactions occurring in very hot stars. I. The synthesis of elements from carbon to nickel"
- Burbidge et al. (1957): "Synthesis of the elements in stars"
- Chandrasekhar (1931): "The maximum mass of ideal white dwarfs"
- Abbott et al. (2017): "GW170817: Observation of gravitational waves from a binary neutron star inspiral"
- Kasen et al. (2017): "Origin of the heavy elements in binary neutron-star mergers from a gravitational-wave event"
Real basis
Big Bang nucleosynthesis: the game's element table has 3 elements that come mainly from here, including hydrogen, helium and lithium.
Cosmic-ray spallation: the game's element table has 2 elements that come mainly from here, including beryllium and boron.
Low-mass stars (s-process): the game's element table has 24 elements that come mainly from here, including carbon, nitrogen, fluorine, rubidium, strontium, yttrium, zirconium, niobium, molybdenum, cadmium, indium, tin and others.
Massive stars (core-collapse supernovae): the game's element table has 22 elements that come mainly from here, including oxygen, neon, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, argon, potassium, calcium and others.
White dwarf explosions (Type Ia supernovae): the game's element table has 6 elements that come mainly from here, including vanadium, chromium, manganese, iron, cobalt and nickel.
Neutron star mergers (r-process): the game's element table has 26 elements that come mainly from here, including ruthenium, rhodium, palladium, silver, antimony, tellurium, iodine, xenon, cesium, samarium, europium, gadolinium and others.
Radioactive decay of uranium and thorium: the game's element table has 7 elements that come mainly from here, including polonium, astatine, radon, francium, radium, actinium and protactinium.
Synthesized: the game's element table has 28 elements that come mainly from here, including technetium, promethium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium and others.
Related research
These studies relate to this topic but are not direct proof of this page.
The αβγ paper: Alpher and Gamow calculated how light elements formed in the Big Bang, and Bethe's name was added to make “αβγ.”
Source: Alpher, Bethe & Gamow, Physical Review 1948, "The origin of chemical elements"
What powers the stars: Bethe calculated that stars shine by nuclear fusion, solving the puzzle of how the Sun can burn for billions of years.
Source: Bethe, Physical Review 1939, "Energy production in stars"
The Chandrasekhar limit: A white dwarf has a maximum mass, about 1.4 solar masses. Beyond it, the star is doomed to keep collapsing.
Source: Chandrasekhar, The Astrophysical Journal 1931, "The maximum mass of ideal white dwarfs"
B²FH: This hundred-page paper explained, step by step, how stars forge the elements of the periodic table. We are all stardust, and this is where that idea starts.
Source: Burbidge, Burbidge, Fowler & Hoyle, Reviews of Modern Physics 1957, "Synthesis of the elements in stars"
Hoyle's prediction: For stars to make enough carbon, Hoyle predicted that carbon-12 must have a special energy level, which experiments then confirmed.
Source: Hoyle, The Astrophysical Journal Supplement 1954, "On nuclear reactions occurring in very hot stars. I. The synthesis of elements from carbon to nickel"
Kilonova: The first time the same cosmic event was both “heard” and “seen”: the merger of two neutron stars.
Source: Abbott et al., Physical Review Letters 2017, "GW170817: Observation of gravitational waves from a binary neutron star inspiral"
Where gold comes from: The material thrown out by neutron star mergers contains large amounts of heavy elements. The gold on your ring probably came from such a collision.
Source: Kasen et al., Nature 2017, "Origin of the heavy elements in binary neutron-star mergers from a gravitational-wave event"