Steward Observatory/NSF’s NOIRLab Joint Colloquium Series: Why Do Galaxies Have Spiral Arms?

Dr. Jerry Sellwood, Affiliate Professor/Distinguished Professor Emeritus Steward Observatory/Rutgers University

Abstract: The cause of the graceful spiral arms in many galaxies has, and largely remains, an outstanding theoretical challenge. It is natural to expect a spiral response in a shearing disk to an external perturbation, but too strong a kick induces a persistent bar, while a mild nudge does little. Bars themselves have often been cited as drivers of spiral arms, but a driven spiral pattern would need to corotate with the bar which is frequently not the case. Therefore, the majority of spirals probably result from self-excited instabilities in the disk. While simulations of isolated, unbarred, cool stellar disks have long manifested spirals, we have only recently been able to understand how they arise. Finding evidence from real galaxies that could determine whether the mechanism identified in the simulations is the cause of spirals in nature is a separate challenge.

Graduate students will meet with the colloquium speaker for lunch on Sept. 22nd at 12:00 PM (AZ) in the Steward Observatory tea area.


3:30 p.m. Sept. 22, 2022