🌟 Star Evolution 2D

The physics is identical — the same mass-dependent stage tables, the same t ≈ 10 Gyr × M⁻²·⁵ lifetime scaling, and the same Hertzsprung-Russell track. Only the rendering differs: this version draws the star and its evolutionary diagram on a flat 2D canvas instead of a rotatable WebGL scene, which is lighter to run and keeps the HR diagram permanently visible without needing to reposition a 3D camera.

Mass sets the core temperature and pressure a young star ignites at, which in turn sets its luminosity (L ∝ M³·⁵) and how fast it exhausts its hydrogen (t ∝ M⁻²·⁵). Below about 8 solar masses a star sheds its envelope gently and leaves a white dwarf; between roughly 8 and 25 it explodes as a supernova and leaves a neutron star; above about 25 the collapsing core cannot be held up by any known pressure and forms a black hole.

Mass (0.1–50 M☉) chooses the entire evolutionary path and final remnant before the run starts. Age is a 0–100% timeline scrubbing from the molecular cloud at the start to the remnant at the end, so you can either step through each stage by hand or let Animate play it automatically.

It plots luminosity (in solar luminosities, log scale, vertical axis) against surface temperature (in kelvin, horizontal axis, hot on the left — the historical convention). Real stars cluster into bands: the main sequence running diagonally, giant and supergiant branches at upper right, and the white dwarf region at lower left. The moving dot is exactly where your simulated star sits right now.

The stage progression, temperatures, luminosities, radii and the mass–luminosity and mass–lifetime scaling relations reflect real astrophysics and match the 3D version's model exactly. Transitions between tabulated stages are smoothed by logarithmic interpolation and the whole lifetime is compressed onto one slider, so it is a faithful qualitative and order-of-magnitude teaching model rather than a full numerical stellar-structure code.

A neutron star packs roughly a solar mass into a radius of about 10 km, and a black hole's event horizon is even smaller — both are drawn near the bottom-left of the display and diagram alike, at low apparent radius, because the log-scaled radius mapping makes stellar and remnant sizes comparable on screen despite spanning nine orders of magnitude in reality.