Speedy galaxy evolution

Abstract

Mature features are detected in an early galaxy The processes that transformed small, turbulent, relatively unstructured protogalaxies into rotating spiral or giant elliptical galaxies are not well understood. Most galaxies are expected to go through a spiral-like phase, maturing into an elliptical structure. Many local spiral galaxies have a classic rotating disk of young stars as well as a “bulge” of older red stars at their centers; these two features are considered to be signatures of galaxies that have evolved from their original primordial forms. Unfortunately, these features are challenging to directly detect, particularly in the very distant (i.e., early) Universe. On page 713 of this issue, Lelli et al. (1) report a galaxy that had evolved features (both a disk and a bulge) when only 1.2 billion years had elapsed since the Big Bang (∼12.5 billion years ago) (see the figure). This finding suggests that the processes that generate the key features of a mature galaxy arose more rapidly than has been thought.