Stellar Evolution and Hertzsprung–Russell Diagram Simulator
Equations in this simulation
| L | luminosity (Sun = 1) | L = 4πR²σT⁴: a star twice as hot gives off 16 times as much light from each square meter | |
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| R | radius (Sun = 1) | drawn as the cube root, so that giants and white dwarfs both fit on the screen | |
| T | surface temperature | sets the color: red below about 3,500 K, white near 6,000 to 10,000 K, blue above |
With the current values:
| M | Mass of the star (Sun = 1) | the mass–luminosity relation: a star ten times the Sun’s mass is thousands of times brighter |
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With the current values:
| t_MS | time on the main sequence | fuel divided by the rate it is burned; the lifetime shown comes from stellar models |
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With the current values:
| M_WD | mass of the white dwarf left behind | an empirical fit for stars below about 8 solar masses; no white dwarf can exceed the Chandrasekhar limit of about 1.4 solar masses |
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With the current values:
How to use the stellar evolution simulator
- Choose the mass of a star, from a tenth of the Sun’s to forty times it. It starts on the main sequence, burning hydrogen in its core, and ages through each stage, a few seconds for each; press Next stage to move on, or change the speed. The star on screen swells, shrinks and changes color, drawn at the cube root of its radius so giants and white dwarfs both fit.
- The chart is the Hertzsprung–Russell diagram: luminosity up, surface temperature along, hot stars on the left. The star’s path is drawn in blue, with the main sequence as a gray band and the Sun’s own track dashed. The results give the age, luminosity, temperature, radius, the time on the main sequence and what will be left at the end.
- Compare the masses: the Sun becomes a red giant and then a white dwarf, a star of 15 solar masses becomes a red supergiant and explodes as a supernova leaving a neutron star, and one of 40 ends as a black hole. A red dwarf of 0.1 solar masses outlives the universe so far. The Blackbody Radiation Simulator shows why temperature sets a star’s color.
Frequently asked questions
What is the Hertzsprung–Russell diagram?
A chart of stars by luminosity against surface temperature, drawn by Ejnar Hertzsprung and Henry Norris Russell around 1910. Most stars lie on a diagonal band, the main sequence, from hot bright blue stars to cool faint red dwarfs. Giants and supergiants sit above it, white dwarfs below. A star’s position tells you its stage of life.
Why do massive stars live shorter lives?
A star’s luminosity rises roughly as the 3.5th power of its mass, so a star ten times the Sun’s mass has ten times the fuel but burns it thousands of times faster. The Sun will spend about 10 billion years on the main sequence, a star of 10 solar masses about 20 million.
What will happen to the Sun?
In about 5 billion years it will run out of hydrogen in its core, swell into a red giant large enough to swallow Mercury and Venus and perhaps Earth, burn helium for about 100 million years, and then shed its outer layers as a planetary nebula. Its core will be left as a white dwarf about the size of Earth, slowly cooling.
What decides whether a star ends as a white dwarf, neutron star or black hole?
Its mass. Stars below about 8 solar masses leave white dwarfs, which can be no heavier than about 1.4 solar masses. More massive stars build cores that collapse in a supernova into a neutron star; the most massive leave black holes. The exact boundaries depend on how much mass the star loses in winds and are still uncertain.
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.