TJO Newsletter Summer 2017
PLAYING GOD By Danielle Skinner
Ever since astronomers have observed the skies, they Cosmological simulations, and simulations generally, have been restrained by the physical limitations of their have assisted astronomers and physicists in answering some instruments as well as our location in the Cosmos. For example, big questions. How are planets formed? How do galaxies fantastic images can be taken of nearby, or low redshift, evolve with time? How does the large-scale structure of the galaxies showing the extreme detail of the structure of the universe form? What is dark matter and how would it interact galaxy, but the same sort of detailed image is harder to achieve with known types of matter? Questions like these are difficult for a galaxy that is very far away. Typically, galaxies at high to answer using only observations. But with simulations, a redshifts will appear as a small blob and won’t be highly scientist has the ability to play God. Cosmological simulations, resolved (See figure 1). Since there are a large number of or n-body simulations, are built to model and accurately galaxies spread out between us and the edge of the observable simulate certain processes that go on in the universe. Generally, universe, observing galaxies at various distances can give these simulations model the motions of n-number of particles astronomers an understanding of how galaxies of all types (hence the name, “n-body”), under the influence of gravity and evolve with time. But, it is difficult for astronomers to really other forces a scientist may want to analyze3. The objects that understand the physics that drive the evolution of high redshift are modelled can be particular known ones or hypothesized galaxies. To help with this problem, astronomers and physicists particles, like the electron, candidates for dark matter, or dust have employed a technique straight out of science fiction - particles, or they can be larger objects in the universe, like stars, cosmological simulations1, 2. or black holes. By translating the equations of physics into lines of code, astrophysicists can model a variety of mechanisms that go on in the universe.
Here at UW, the scientists in the N-body shop in the Astronomy department are hard at work trying to answer some of these questions. Topics being explored range from planet formation and planetary disc formation, galaxy formation and Figure 1: Andromeda galaxy on the left and GN-z11 on the evolution, to black hole accretion, dark matter, and dust right. Andromeda is our closest neighbor galaxy, sitting at attenuation. In particular, a recent simulation was just a redshift of z = -0.001 (778 kpc away). GN-z11 is the completed by graduate student Michael Tremmel in the N- farthest galaxy that Hubble has observed, with a redshift of body shop, called Romulus25. This simulation models a cube 7 z = 11.09 (4.8 billion pc in light travel distance). Both are of the universe, 25 megaparsecs (or 8.2x10 light years) per galaxies, yet they represent two extremely different periods side, and allows astronomers to study galaxy formation, large in time. scale evolution, and a variety of other physics. An image of the simulation can be seen in the left panel of Figure 2, where you (Left: https://apod.nasa.gov/apod/ap140730.html, Right: can see galaxies clumping together and forming at the bright https://www.nasa.gov/feature/goddard/2016/hubble-team- red locations. The right panel of Figure 2 is an actual map of breaks-cosmic-distance-record) galaxies in the universe, taken by the Sloan Digital Sky Survey (SDSS)4, and one can see the similarities between the two images. While this is only one example of a cosmological TJO Newsletter Summer 2017 simulation, simulations like these help scientists understand the Simulations allow scientists to model and observe actual physics and mechanisms which govern the universe that whatever type of processes physics will allow. These we observe. For more information on the work being done in simulations can transport the user and the observer to new the N-body shop at the University of Washington, see: locations and distant times. By playing God, scientists can http://depts.washington.edu/astron/spotlight/research- model their own universe in hopes to answer some of the spotlight-n-body-shop-simulates-the-universe/ biggest questions of the Cosmos. While only astronomical simulations were mentioned here, simulations of all types are used throughout all branches of science. As computing becomes more advanced, simulations will only become more complex, accurate, and useful, and perhaps one day, we will be able to simulate human life itself.
Figure 2: Left: A snapshot from the Romulus25 simulation at a redshift of 2. Right: A map of galaxies (Earth is in the SOURCES CITED middle) taken by the Sloan Digital Sky Survey out to a 1 Lerner, Louise. Researchers model birth of universe in one redshift of ~ 0.15. Notice how the structure of the two of largest cosmological simulations ever run. 29 images looks similar. October 2015.
Not only are simulations used to answer hypothetical 3 N-body Simulation. n.d. 28 May 2017. questions, but they are also used to predict what telescopes will