Galactic Archaeology

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Science  19 Oct 2012:
Vol. 338, Issue 6105, pp. 333-334
DOI: 10.1126/science.1227302

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Galactic archaeologists sift through stellar fossil records to uncover the history of our nearby universe. Akin to archaeologists interpreting the customs of ancient civilizations, clues are assembled of past events in the galaxy's lifetime based on the remnants observable today. In most galactic archaeology studies deciphering the histories of spiral galaxies like our own Milky Way, a critical assumption made for the past 30 years was that stars born in disks do not venture far from their original birthplace. The demographics of a population in a given part of the disk (see the figure) then yield a complete record of the galaxy's past, turning star counts into cosmologically relevant tools. The assumption that stars mostly stay put throughout their lives therefore carries enormous implications and wields considerable power. However, recent work on galactic disk dynamics shows that this critical assumption is likely flawed and instead many stars are expected to wander considerable distances throughout their lives. This process of radial migration affects the entire galactic disk, and if theoretical expectations are confirmed by observations, its consequences are integral to fields as diverse in scope and scale as solar system science and extragalactic galaxy formation. It was with this in mind that a workshop dedicated specifically to the issues related to radial migration in disk galaxies took place earlier this year (1).