Early formation and recent starburst activity in the nuclear disk of the Milky Way

The nuclear disk is a dense stellar structure at the centre of the Milky Way, with a radius of ~150 pc (ref. ¹). It has been a place of intense star formation in the past several tens of millions of years^1-3, but its overall formation history has remained unknown². Here, we report that the bulk of its stars formed at least 8 Gyr ago. After a long period of quiescence, a starburst event followed about 1 Gyr ago that formed roughly 5% of its mass within ~100 Myr, in what may arguably have been one of the most energetic events in the history of the Milky Way. Star formation continued subsequently on a lower level, creating a few per cent of the stellar mass in the past ~500 Myr, with an increased rate up to ~30 Myr ago. Our findings contradict the previously accepted paradigm of quasi-continuous star formation at the Galactic Centre⁴. The long quiescent phase agrees with the overall quiescent history of the Milky Way^2,5 and suggests that our Galaxy's bar may not have existed until recently, or that gas transport through the bar was extremely inefficient during a long stretch of the Milky Way's life. Consequently, the central black hole may have acquired most of its mass already in the early days of the Milky Way.