STEP 1 / CHOOSE A STAR
Mass decides everything.
White dwarf: below 8Neutron star: 8 to 20Black hole: above 20
Loading the 3D model…
This stage has no layers inside to cut away.
THE HERTZSPRUNG–RUSSELL DIAGRAM
Brightness against temperature
Hot stars are on the left. The dashed lines join stars of the same radius: a star that moves along one keeps its size, and one that crosses them is growing or shrinking.
THE WHOLE LIFE, TO SCALE
Where the time goes
A model is an explanation, not a photograph.
The numbers come from standard physics: mass–luminosity and mass–radius relations for the main sequence, the Stefan–Boltzmann law linking brightness, radius and temperature, free-fall and Kelvin–Helmholtz timescales, and measured relations for the mass of the remnant. The star's color is the color of a hot body at its surface temperature, with the color strengthened so that cool and hot stars are easy to tell apart.
Sizes are compressed. Real stars range from 20 km to over 1000 times the width of the Sun, so the 3D view squeezes that range enormously; the small inset always shows the true scale. Cutaway layers are widened so you can see them: the core of a giant is really less than a thousandth of its radius. Time is compressed too: every stage plays for a few seconds, whether it really lasts a day or ten billion years.
The boundaries at 8 and 20 solar masses are approximate. They depend on what the star is made of, how fast it spins and whether it has a companion. The tracks after the main sequence are simplified, and stars lighter than about 0.5 solar masses live so long that their final stages are predictions that nobody has observed.