Stellar Life Cycle & H-R Diagram Simulator
Build a star by mass and watch it evolve on the Hertzsprung-Russell diagram from the main sequence to its final fate.
How to use: drag the mass slider to build a star, then press Evolve to fast-forward through its life on the Hertzsprung-Russell diagram and see its main-sequence lifetime and final fate.
Challenge 1: a star that dies fast
Set the mass so the main-sequence lifetime is under 50 million years (a massive, short-lived star).
Challenge 2: predict a white dwarf
Set the mass so the star's fate will be a white dwarf (mass below about 8 solar masses), then Evolve and confirm.
About the Stellar Life Cycle & H-R Diagram Simulator
Free stellar life cycle & h-r diagram simulator. Build a star by mass and watch it evolve on the Hertzsprung-Russell diagram from the main sequence to its final fate. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for astronomy, the stellar life cycle & h-r diagram simulator runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Build a star by mass and watch it evolve on the Hertzsprung-Russell diagram from the main sequence to its final fate. Use it to explore astronomy ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Stellar Life Cycle & H-R Diagram Simulator
- Use the controls to change Mass (solar masses). The simulation reacts instantly.
- Press "⏩ Evolve", "Reset star", "Reset to defaults", "📄 Lab Report" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Set the mass to 20 solar masses and evolve - watch how fast it races through its life.
- Set the mass to 0.3 solar masses and compare its lifetime to the Sun's.
- Evolve a 1 solar mass star and watch it become a red giant before ending as a white dwarf.
- Find the smallest mass whose fate is a black hole.
Key ideas you can learn
- A star's mass sets almost everything about it: luminosity scales roughly as L ∝ M^3.5, so a small mass difference means a huge brightness difference.
- Main-sequence lifetime scales as t ∝ M / L ∝ M^-2.5, so massive stars burn hot, bright and fast while low-mass red dwarfs sip their fuel for trillions of years.
- On the H-R diagram, hot blue stars sit on the upper left and cool red stars on the lower right; most stars, for most of their lives, sit on the main-sequence band running from upper left to lower right.
- A star's fate depends on its mass: under about 8 solar masses it ends as a white dwarf after a red giant phase; between about 8 and 20 it explodes as a supernova leaving a neutron star; above about 20 it collapses into a black hole.
Where this is used in the real world
Astronomers use exactly this mass-luminosity-lifetime relationship, calibrated against real H-R diagrams of star clusters, to estimate a cluster's age from where its stars have started peeling off the main sequence.
Who is this simulation for?
Students, teachers and curious learners of all ages.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
Why do the most massive stars have the shortest lives despite having the most fuel?
Luminosity grows much faster than mass (L ∝ M^3.5), so a massive star burns its larger fuel supply at a hugely disproportionate rate, and the burn rate wins - net lifetime falls as mass rises.
Why does our Sun's fate differ from a star 15 times more massive?
The Sun, at 1 solar mass, lacks the core mass needed to fuse elements beyond helium under high enough pressure, so it sheds its outer layers as a planetary nebula and leaves a white dwarf; a 15-solar-mass star has enough core mass to fuse all the way to iron and then collapses catastrophically in a supernova, leaving a neutron star.
Is the Stellar Life Cycle & H-R Diagram Simulator free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Stellar Life Cycle & H-R Diagram Simulator work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.