Astronomers face a unique problem. As all astrophysical events occur on very long time scales and over very large distances, they cannot really perform experiments to test their theories as chemists, biologists and engineers would do in their laboratories. Observations from telescopes can only tell us what a given galaxy looks like now and not what it was like in the past.

That’s why scientists use computer simulations to see how stars or galaxies evolve over the history of the universe. By creating multiple simulations with different physical theories, astrophysicists can eliminate models that lead to a virtual universe different from ours. This approach gives astronomers a better understanding of the physical processes at stake in galaxy formation.

Here are science’s most mesmerizing virtual universe simulations:

Illustris Simulation

An ongoing series of astrophysical simulations run by an international collaboration of scientists, the goal of the Illustris project is to study the various processes behind galaxy formation and evolution in the universe with a comprehensive physical model.

EAGLE Simulation

The EAGLE simulation has landed, and with it 6.8 billion particles that ran for nearly six weeks on one of Europe’s largest supercomputers. Filling 32 terabytes (TB) of RAM and producing 500 TB of data (or roughly five thousand times the size of the English-language Wikipedia), the project was enabled by access to world-leading supercomputing facilities.

KIPAC/SLAC/CITA Simulation of Reionization

The Epoch of Reionization (EOR) was that moment in our universe’s history when the emergence of luminous objects helped ionize what was up until that point a neutral intergalactic medium. What kind of objects, exactly? Stars, galaxies, quasars, or some mixture of all three. Through the further study of reionization we hope to learn more about the process of structure formation in the universe and clusters of galaxies, while at the same time find evolutionary links between the remarkably smooth matter distribution of our universe’s earlier stages.

Visualization of Reionization from the the Kavli Institute for Particle Astrophysics and Cosmology by Ralf Kaehler (KIPAC), Marco Alvarez (CITA), Tom Abel (SLAC, Stanford). Simulation: Marcelo Alvarez (CITA), Tom Abel(SLAC, Stanford).

KIPAC/SLAC Dark Matter Streams

Dark matter streams may (or may not) exist in the Milky Way, but here we have a simulation of the formation of a large cluster of galaxies, from the early universe until the present day. To better illustrate the effect the expansion has been scaled out to show how the gravitational collapse into filamentary structure and individual galaxies form and fall in to the cluster’s center, where the filaments intersect. This particular region is similar to a large cluster of galaxies in the local universe, such as the Virgo Cluster or the Coma Supercluster.

Visualizations of Dark Matter / Large Scale Structure by Ralf Kaehler (KIPAC) and Tom Abel (SLAC, Stanford).

Cover image credit: Ralf Kähler