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 years1-3, 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 Way2,5 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

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 years1–3, 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 Way2,5 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. © 2019, The Author(s), under exclusive licence to Springer Nature Limited.The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 614922. F.N.-L. acknowledges financial support from a MECD pre-doctoral contract, code FPU14/01700. We acknowledge financial support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). R.S., A.T.G.-C. and B.S. acknowledge financial support from the national grant PGC2018-095049-B-C21 (MCIU/AEI/FEDER, UE). F.N. acknowledges financial support through Spanish grants ESP2015-65597-C4-1-R and ESP2017-86582-C4-1-R (MINECO/ FEDER) and from the Spanish State Research Agency (AEI) through the Unidad de Excelencia “María de Maeztu” -Centro de Astrobiología (CSIC-INTA) project no. MDM-2017-0737. N.N. acknowledges support by Sonderforschungsbereich SFB 881 ‘The Milky Way System’ (subproject B8) of the German Research Foundation (DFG).Peer reviewe