CCA Colloquium: Jason Sanders

Date


Title: A Biased History of our Galaxy

Abstract: Our home galaxy, the Milky Way, offers an extraordinary opportunity to study a fairly typical galaxy in exquisite detail. Thanks to Gaia and complementary large-scale photometric and spectroscopic surveys, we now have access to catalogues containing millions to billions of stellar measurements — positions, velocities, compositions and even ages. These data, particularly the ages, allow us to reconstruct the Galaxy’s timeline and place it in the broader context of galaxy evolution across cosmic time. In this talk, I will explore four key chapters in that timeline. First, I will discuss the Gaia-Sausage-Enceladus (GSE) merger and the associated “Splash” connecting these events to the present-day structure of the halo. Second, I will focus on the Galactic bar: when it formed, whether its origin is linked to the GSE merger and its ongoing dynamical impact on the Galaxy today. Third, I will describe the growth and restructuring of the Galactic disc through inside-out formation and radial migration, possibly driven by the bar. Finally, I will consider how ongoing interactions, such as with the Large Magellanic Cloud, continue to reshape the Milky Way. By weaving together stellar ages with dynamics and chemistry, we can now tell a remarkably detailed story of how our Galaxy came to be and how it continues to evolve.

November 14, 2025

Jason Sanders: A Biased History of our Galaxy

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