Star Cluster Evolution

H-R diagram
H-R (or Hertzsprung-Russell) diagrams of real star clusters are used by astronomers to study the stars' ages, distances and chemical compositions.
An H-R diagram plots the stellar surface temperatures (bluer is hotter and towards the left on the plot) against the stellar luminosities (brighter is towards the top of the plot). In these units our Sun has a surface temperature of about 5,800 Kelvin and a luminosity of 1.

View in space
This plot is a projection of star positions in space and tracks the cluster as it orbits around the Galaxy.
In this simulation the Galactic center is towards the left of the screen, and the cluster's orbit is aligned roughly with the vertical direction.
Pinch to zoom in or out. Note that the star sizes are not to scale and are dramatically inflated for ease of viewing.

Mouseover the time axis to move forward and backwards through time. Click on a star to see its properties. Click on the orange tick labels of the time axis to explore a real cluster of a specific age.

Our Sun likely formed in a small cluster of stars that dissolved many years ago. Here you can interact with a computer simulation of a 100-star cluster similar to our Sun's birthplace, as it evolves in time from birth until the present day (at an age of 5 billion years).

In the H-R diagram on the left, watch as the most luminous stars quickly evolve from the "main sequence" to become "giants". Indeed, all stars evolve in time, with the most massive (and therefore most luminous) evolving most rapidly. You may also notice two different branches of main-sequence stars; the branch to the red (right) on the plot is composed of binary stars - 2 stars bound by their own mutual gravity and orbiting each other, but unresolved from Earth at the distances to most clusters. Can you find other stars that don't follow the standard evolutionary sequence?

In the middle, you see the stars moving in space as the cluster orbits around the Galaxy. Watch as the cluster quickly dissolves under the tidal pull of our Galaxy and is drawn into a tight line, displaying "tidal tails" similar to those observed in real dissolving star clusters. You may also notice neutron stars leaving the cluster early at high velocities, due to large kicks imparted by the stars' very energetic supernovae explosions. Our Sun likely escaped from its birth cluster like the majority of the stars in this simulation: slowly and calmly, and eventually leaving its siblings to live out its life in isolation - which was good news for us!

Credits: This plot has been created using D3 and has been inspired by Also it uses the World Wide Telescope. Data was simulated by Aaron M. Geller and visualized by Ester Pantaleo; the project was led by Mark SubbaRao. Source code is available here.