Eliot Circular

How a Galaxy Evolves

By Noah Muldavin ’13

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 time-scale 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 history of civilization.

Recently astrophysicists have used computers to speed things up. For my thesis with Prof. 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 involved 20,000 stars in a disk hundreds of thousands of light-years across. After running for a week on a powerful multi-core 3 GHz Apple Mac Pro, the program yielded a six-minute video that represents billions of years of evolution. 

The result is breathtaking. You’ll see a spiral pattern develop quickly, then slowly fade away, showing 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.