The Star Formation History of the Milky Way

TL;DR

This paper reviews the star formation history of the Milky Way, highlighting the formation timescales of different components and discussing observational constraints and inconsistencies in current data.

Contribution

It synthesizes current observational data on the Milky Way's star formation history, emphasizing the formation periods of various galactic components and challenging some existing galaxy formation models.

Findings

Halo and globular clusters are almost exclusively old.

Outer bulge likely formed early, data is inconsistent.

Inner bulge/disk is actively forming today.

Abstract

Quantification of the Galaxy's star formation history involves both the duration and the rate of formation, with these parameters being known with different precision for different populations. The early rate of star formation is knowable from modelling chemical element data, the recent rate directly from isochrone analyses of colour-magnitude data. The field halo and globular clusters are almost exclusively old, and formed in at most a few Gyr. The outer bulge probably formed in a short period long ago -- extant data is inconsistent, while the inner bulge/disk is forming today, and has continued to form over time. Only very limited data is available on the inner disk. The outer disk near the Sun seems as old as the halo. The earliest extended disk, which forms the thick disk today, seems to have been in place very early, an observation which is not simply consistent with some galaxy formation models.