Sallyportal: Madly Blogging Reed

How a Galaxy Evolves

Humankind’s view of the cosmos, however magnificent, is fundamentally static. Astrophysicists know that distant astronomical objects (stars, nebulae, galaxies) are in constant motion, but this is invisible to human eyes because it takes place on a timescale which is unimaginably vast. In fact, except for the moon, the planets, and the occasional comet, the night sky has looked essentially the same for the entire history of human civilization.

Recently astrophysicists have used computers to speed things up. For my thesis with  Johnny Powell [physics 1987–], I wrote a computer program to simulate the evolution of a typical spiral galaxy. The central premise is that by calculating the gravitational forces acting on a relatively small number of stars, we can simulate the evolution of a real galaxy, which consists of hundreds of billions of stars.

My simulation involves 20,000 stars in a disk that is hundreds of thousands of light-years across. The disk is lodged in a spherical cloud of dark matter, though this isn’t visualized here. The video runs for six minutes, but represents billions of years of evolution (perhaps the entire lifetime of a galaxy). It required about a week to compute on a powerful multi-core 3 GHz Apple Mac Pro.

The result is something beautiful and useful: a prediction of how a galaxy might move according to physical theory as we understand it. You’ll see a spiral pattern develop quickly, then slowly fade away. The main result here is that spiral arms can form in an isolated galaxy (one not interacting with other galaxies). To me, the fact that this recognizable pattern emerged in such an artificial simulation is powerful evidence that our quest to understand the motion of galaxies is on the right track.

[This post is part of an occasional series about seniors and their theses. —Ed.]

Tags: physics, astronomy, thesis

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