Equation 8 · Part 4 · Nucleosynthesis Is Descent With Modification
subtraction
subtraction
What this part means
Subtract the following term or group from the preceding one. A leading minus marks a negative quantity.
Its job in the formula
Subtract the following term or group from the preceding one. A leading minus marks a negative quantity.
Full expression→subtraction→Article meaning
The passage around this formula
Zoom out from individual nuclei to the gas that forms whole generations of stars, and the genealogy becomes explicit rather than metaphorical. Astronomers describe the abundance of everything heavier than helium in a star or a cloud of gas with a single number, metallicity, defined through the mass fractions of hydrogen ( X ), helium ( Y ) and “metals” ( Z ): . A gas cloud’s metallicity is, quite literally, an inherited character: it is the accumulated, largely unerased record of every previous generation of stars that lived, burned and returned processed material to the interstellar medium before that cloud collapsed to form new stars. The first stars, Population III,…
Learn the underlying idea
Addition combines quantities; subtraction measures the signed difference between them. Parentheses show what is combined before the rest of the expression is evaluated.
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Sources cited in the surrounding passage
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