Rubin Planetarium Video - Galaxy Evolution

What does it take to build a galaxy? Galaxies, including our own Milky Way, have a dynamic and chaotic history. A dramatic sequence of events is necessary to transform dark matter and gas into the beautiful spiral galaxies we see today. This video shows a computer simulation that demonstrates how a galaxy like our Milky Way formed and changed over 13.8 billion years. The simulation begins shortly after the Big Bang, and ends with the galaxy looking as it would now. The simulation also includes the expansion of the Universe, which affects how a galaxy forms. 

Galaxies are much more than collections of stars. This visualization shows different types of material, including stars, gas, and dark matter. Astronomers have discovered that dark matter is necessary for galaxies to form. Each type of material is indicated by a different color. Cool, dense gas is shown as green. Hot gas is orange and violet. Stars are shown on a blue-yellow color scale. Finally, dark matter is shown as an inverted white-to-black grayscale, where black shows the dense concentrations of dark matter. Note that these are not the real colors of the materials in question. Instead, they are intended to clearly show whatʼs happening in this computer simulation.

One of the major science goals for LSST is to probe the nature of dark matter and dark energy. LSST will do this by discovering and characterizing about 20 billion galaxies. By mapping their locations, cataloguing their masses, and studying their influence on the distortion of space-time, LSST will gain new insight into how galaxies form, and how dark matter and dark energy influence the clustering of galaxies on large scales.



This video shows a computer simulation of how a galaxy like the Milky Way formed over the span of billions of years. The current time in the simulation, i.e., how long before the present, is shown along the bottom. The simulation begins just a few hundred million years after the Big Bang occurred. Dark matter (shown in black on a white background) collapses into thin, wispy filaments. The first galaxies begin to form at the intersections of these filaments where the dark matter is most dense. Massive stars forming in these young galaxies quickly explode as supernovae and expel “winds” of hot gas (shown as orange and violet).


At this time the video switches to show the distribution of gas. Cool gas (shown in green) accumulates on the dark matter concentration and forms a spiral-like structure. This is a young, small galaxy that is forming stars at a much higher rate than galaxies do today.


The video now starts to show the distribution of stars (in yellow and blue), all of which have formed since the beginning of this visualization. Here we see the merger of a smaller satellite galaxy and the main galaxy. This is called “galactic cannibalism,” and is one of the ways the main galaxy grows. Gas filaments, shown in green, are disrupted by the galaxies merging.


The distribution of dark matter, seen in black and white, is now shown again. There is a large halo of dark matter in and around the main galaxy. There are also many smaller halos of dark matter associated with small satellite galaxies that are moving at high speed.


The concentration of cold gas is shown again. The gas is stretched into thin filaments flowing into the main galaxy. This gas will eventually settle into a disk, out of which new stars will form. This is approximately the time when the Sun formed in our galaxy.


At this point the simulation stops and we move around the galaxy so we can see its shape and structure. In sixty seconds we have seen 13.8 billion years of galactic evolution, from the start of the Universe until now. The orange and red colors show hot gas that surrounds the galaxy. Dark matter halos are shown in black, some of which contain dwarf galaxies. Stars appear in a disk-like structure surrounding the central bulge. The end result is a galaxy about 100,000 light years across, just like the Milky Way. Notice that the satellite galaxies, gas, and dark matter extend out to much larger distances.

Additional References

  • Schaye, J., Crain, R. A., Bower, R. G., et al. 2015, MNRAS, 446, 521
  • Oppenheimer, B. D., Crain, R. A., Schaye, J., et al. 2016, MNRAS, 460, 2157
  • Benitez-Llambay, Alejandro (2015). py-sphviewer: Py-SPHViewer v1.0.0. Zenodo, 10.5281/zenodo.21703


Fiske Planetarium, University of Colorado Boulder

Benjamin D. Oppenheimer (

Data Sources: This EAGLE (Evolution and Assembly of GaLaxies and their Environments) simulation

was run on the RMACC Summit Supercomputer hosted at the University of Colorado, Boulder.

Special Recognition

Data to Dome initiative

The visualization software used for the simulation is Py-SPHViewer. Py-SPHViewer is under GNU GPL

v3 license, and was started by Alejandro Benitez-Llambay. This work was created for LSST and utilized

the RMACC Summit supercomputer, which is supported by the National Science Foundation (awards

ACI-1532235 and ACI-1532236), the University of Colorado Boulder, and Colorado State University.

The Summit supercomputer is a joint effort of the University of Colorado Boulder and Colorado.

About the Video

Release date:April 7, 2023, 10:40 a.m.
Duration:01 m 38 s
Frame rate:30 fps

About the Object


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