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Modeling Galaxies in Space and Time


To understand how the modern Universe came to be, astronomers turn to computer models, programs that follow the physical laws of the Universe. Computer models can be run backward to reconstruct the past or forward to predict the future. A team of researchers from the Institute for Computational Cosmology at Durham University in the UK recently used computer models to simulate how the Universe’s big galaxies have changed over billions of years.

Galaxy Formation Simulation Millennium Run

Simulating the joint evolution of quasars, galaxies and their large-scale distribution with the Millennium Run code. Projected density field for a 15 Mpc/h thick slice of the redshift z=0 output. The overlaid panels zoom in by factors of 4 in each case, enlarging the regions indicated by the white squares.

Credit: Volker Springel, 2004

Their starting point was 500 million years after the Big Bang. At this time, big star-forming galaxies built up from gas that was clumping along filaments of dark matter, an invisible substance that pervades the Universe. The galaxies coalesced at dense points of dark matter where its gravity was strongly attractive. The team let the dark matter and the galaxies in the model evolve to the present day. The computational effort required both the Millenium Simulation, a simulation of how structures grow in dark matter, and a computer model that mimics how normal matter, such as gas, behaves.

The results showed that galaxies were at their peak of star formation somewhere between 2 billion and 3 billion years after the Big Bang, and have tapered off in modern times. Today, galaxies are far less active because most of their gas is already locked up in stars. Now, researchers can compare the computer model’s results with modern telescope maps of the Universe, such as those from VISTA, a new sky survey telescope at Chile’s Paranal Observatory. These comparisons can help the team gauge the accuracy of their galactic time machine.

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