16.1
Gravity compresses. Pressure supports.
A long-lived star is not static matter. It is a self-gravitating fluid in continual local balance: pressure changes with radius so that each layer can support the weight above it.
inward gravitypressure supportthermal / virial scale
16.2
More mass means far more light—and much less time.
On the main sequence, stellar mass strongly controls luminosity. Massive stars have more fuel, but they use it disproportionately faster.
16.3
The H–R diagram turns temperature and luminosity into a map of stellar states.
Move one point through the Hertzsprung–Russell plane. The Stefan–Boltzmann relation then tells you what radius a spherical emitter would need for that luminosity and effective temperature.
16.4
The periodic table has more than one birthplace.
There is no single “stellar factory” that makes every element. Different nuclei are favored by different temperatures, densities, reaction networks and astrophysical environments.