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∑ The maths › Stars forge the elements · open the lab →

Stars forge the elements: the maths

Mostly published data: which elements a star of each mass makes, how long it lives, and where each element in the Solar System came from. The moving pictures are pictures. One sum is computed: how much of your body was made in stars.

Equations

share from stars = 1 − Σelements (body share × Big-Bang share) / Σ (body share)
Your mass by origin: each element's share of your body, times the share of that element made by each source.

Constants

body compositionO 65%, C 18%, H 10%, N 3%, Ca 1.5%, P 1% …Emsley (2011)
element originsrounded to the nearest 10%Johnson (2019); Kobayashi, Karakas & Lugaro (2020)
stage timesfor a 25-Sun starWoosley, Heger & Weaver (2002)

Data, not a simulation: the numbers here are published values, shown as they are. The sources below are the tables.

Worked examples ✓ checked on every change

Heaviest element a Sun-like star's core makesOxygenstellar models: the Sun stops at carbon and oxygen
…a 12-Sun star'sNickelcore fusion stops at the iron group
Your mass made in stars90%Emsley (2011) × Johnson (2019): all but the hydrogen

The app's test suite puts the lab in each setup, reads the lab's own result, and fails if it strays from these values.

What's simplified

  • Which stage makes which element is rounded; the mass thresholds are rounded from stellar models and the 8–10 Sun boundary is uncertain.
  • Origin shares are for the Solar System, rounded to 10%.

Where it breaks

Where the models disagree: the split of heavy elements between colliding neutron stars and rare collapsing stars (contested).

Sources: S. E. Woosley, A. Heger & T. A. Weaver, RMP 74, 1015 (2002); J. A. Johnson, Science 363, 474 (2019); C. Kobayashi, A. I. Karakas & M. Lugaro, ApJ 900, 179 (2020); J. Emsley, Nature's Building Blocks (2011).

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