Galaxy Formation in the Cosmic Web:

Image by Lauren Anderson (lmanders@astro.washington.edu), Fabio Governato (fabiog@astro.washington.edu) and the N-Body ShopThe N-Body Shop research is funded in part by grants from the National Science Foundation and the National Aeronautics and Space Administration.

Gravity is an attractive force causing dark matter and gas to flow along filaments and eventually form galaxies. Galaxies like our own Milky Way form at the intersection of the largest filaments of Dark Matter and gas in the so called ‘cosmic web’. This simulation achieves such a high resolution that we can predict how many stars will form inside individual galaxies.

The N-Body Shop is a theoretical and computational research group founded at the Astronomy Department of the University of Washington in 1995. It now includes several collaborators at national and international institutions, including Prof. Governato & Quinn (UW), Prof. Brooks (Rutgers), Prof. Wadsley (McMaster, CA) and Prof. Pontzen (UCL, UK). Our work focuses on understanding galaxy evolution and the nature and properties of Dark Matter and Dark Energy.

The universe doesn’t fit in a lab; therefore, astrophysicists use super computers to simulate its history and study the complex physics driving the evolution of the galaxies within it. This poster’s image of the ‘cosmic web’ is from such a simulation. It shows the evolving gas distribution within a large patch of the Universe in the so called Cold Dark Matter scenario. In this model Dark Matter and Dark energy contribute to 95% of the mass-energy density of the Universe. Only the remaining 5% (gas and stars) can actually be seen. Our research group, the ‘N-Body Shop’, makes predictions of what astronomers will observe and ties observations to the underlying distribution of dark matter.

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the Gas Distribution.

SIMULATIONS

his image frame spans 10 million light years across and shows the ‘cosmic web:’ the filamentary distribution of matter in the cosmos as predicted by

a computer simulation. The image shows how the Universe looked six billion years after the Big Bang (the Universe today is 13.7 billion years old). The color shading represents the local density of gas, with the bluest shades being the most dense and the darker areas showing the voids: large volumes of space almost empty of gas, dark matter and galaxies. Brightness corresponds to the gas temperature — the brightest patches approaching one million degrees Kelvin. Each hot gas bubble was created by large number of Supernovae, enormous amounts of energy released when massive stars explode at the end of their life cycles. This simulation was computed on NASA’s supercomputer Pleiades using ChaNGa, a parallel tree+hydrodynamics code developed by Prof. Tom Quinn and the N-Body shop.

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As clusters of stars form in collapsing gas clouds, the most massive stars evolve into Supernovae, unstable stars that explode and heat their surrounding gas. During the explosion, heavy atoms fused in the center of the star such as oxygen, iron and carbon are dispersed into space. The hot gas surrounding the explosion has been observed to expand at several hundred km/sec, forming large bubbles. This gas may eventually re-collapse to form a new generation of stars. Our own Solar System formed from material previously processed by Supernovae.

Galaxies as we see them today formed over billions of years. Driven by mutual gravitational attraction, individual galaxies and their surrounding dark matter halos merge, forming more and more massive systems. The largest structures in this image contain galaxies as massive as our own Milky way. Due to a continuing build up of mass, the largest dark matter halos in the present Universe contain hundreds of massive galaxies.

Regions of space that are significantly under dense are called ‘voids’. These are regions where the density of matter is only 10% of the average density of the Universe, or almost a million times less dense than the density inside galaxies like our own. Almost no galaxies form in the voids, and so no hot gas is observed.

These small clouds of hot gas are associated with stars forming in the smallest known galaxies, often referred to as ‘dwarfs’. The smallest dwarf galaxies form only a few hundred thousand stars and consist mostly of Dark Matter. It would take the mass of more than a thousand dwarf galaxies to make a galaxy as big as the Milky Way. The Milky Way and its nearest massive neighbor the Andromeda galaxy are each surrounded by several dozen dwarfs galaxies. Some have only been discovered in the past few years and many remain to be found, too dim to see even with powerful telescopes.