Some 380,000 years after the Big Bang, when light could finally travel freely through space, the early universe was as smooth and featureless as a bowl of consommé. So how did the universe progress from such a dull and unpromising state to its current lumpy configuration full of galaxies and stars and planets?
A recent supercomputer simulation project called EAGLE (Evolution and Assembly of GaLaxies and their Environments) confirms and shows in great detail what has long been suspected. The tiny fluctuations in density in the early universe were magnified by gravity, with dark matter slowly congealing into denser clumps and filaments which then drew in hydrogen and helium gas where it formed into the first stars and galaxies.
The EAGLE simulation starts before the first stars and galaxies formed. Measurements from the COBE, WMAP, and most recently, the Planck space telescopes all show the universe was uniform to one part of 100,000. Other key input parameters to EAGLE include the density of dark matter, the density of “normal” matter made of hydrogen and helium, and the mysterious cosmological constant that causes the expansion of the universe to accelerate.
Using known physics and the composition of the early universe, EAGLE models the formation of galaxy clusters in a volume of of 300 million light-years on a side. That’s large enough to contain 10,000 galaxies of the size of the Milky Way or bigger. It also keeps track of more than 7 billion particles over hundreds of millions of years.
The image at top is a slice through the simulation volume from EAGLE. The color of the intergalactic gas is coded from blue to green to red with increasing temperature. Hot (red) gas is more than 100,000K and overlays the with dark matter structures that pull in the gas and the first stars and galaxies.
The EAGLE simulation is so detailed, it even reveals the basic shape of individual spiral galaxies that coalesce out of hydrogen and helium gas and are held in place by halos of dark matter. The simulated spiral galaxies look remarkably similar to spiral like our Milky Way. The filaments and galaxy clusters and superclusters in the simulation also agree in shape and structure with large-scale observational surveys of galaxy clusters and superclusters. The agreement of the simulation with observation suggests the EAGLE model is on the right track and that cosmologists have a decent understanding of the physics of the formation of the largest structures in the universe.
The EAGLE simulation took more than one and a half months of computer time on the DiRAC-2 supercomputer at Durham University in the United Kingdom. That is serious number crunching.
The above video shows some of the results of the EAGLE simulation. You can also explore for yourself the quite beautiful and complex structure of the universe predicted by EAGLE at this link:
There’s also a free iPad app that allows you to pan around the simulated “sky” from EAGLE and see how gas, dark matter, and galaxies overlap and influence each other. Look for “Cosmic Universe” at the app store.