Howes, L. M.Casey, A. R.Asplund, M.Keller, S. C.Yong, D.Nataf, D. M.Poleski, R.Lind, K.Kobayashi, C.Owen, C. I.Ness, M.Bessell, M. S.Da Costa, GarySchmidt, BrianTisserand, PatrickUdalski, A.Szymański, M. K.Soszyński, I.Pietrzyński, G.Ulaczyk, K.Wyrzykowski, Ł.Pietrukowicz, P.Skowron, J.Kozłowski, S.Mróz, P.2017-08-020028-0836http://hdl.handle.net/1885/122890The first stars are predicted to have formed within 200 million years after the Big Bang, initiating the cosmic dawn. A true first star has not yet been discovered, although stars with tiny amounts of elements heavier than helium ('metals') have been found in the outer regions ('halo') of the Milky Way. The first stars and their immediate successors should, however, preferentially be found today in the central regions ('bulges') of galaxies, because they formed in the largest over-densities that grew gravitationally with time. The Milky Way bulge underwent a rapid chemical enrichment during the first 1-2 billion years, leading to a dearth of early, metal-poor stars. Here we report observations of extremely metal-poor stars in the Milky Way bulge, including one star with an iron abundance about 10,000 times lower than the solar value without noticeable carbon enhancement. We confirm that most of the metal-poor bulge stars are on tight orbits around the Galactic Centre, rather than being halo stars passing through the bulge, as expected for stars formed at redshifts greater than 15. Their chemical compositions are in general similar to typical halo stars of the same metallicity although intriguing differences exist, including lower abundances of carbon.This paper includes data gathered with the 6.5-m Magellan Telescopes located at Las Campanas Observatory, Chile. Australian access to the Magellan Telescopes was supported through the Collaborative Research Infrastructure Strategy of the Australian Federal Government. L.M.H. and M.A. were supported by the Australian Research Council (FL110100012). A.R.C. acknowledges support from the European Union FP7 programme through ERC grant number 320360. Research on metal-poor stars with SkyMapper is supported through Australian Research Council Discovery Projects grants DP120101237 and DP150103294 (principal investigator G.S.D.C.). The OGLE project received funding from the NSC, Poland (MAESTRO grant 2014/14/A/ST9/00121 to A.U.).12 pagesapplication/pdfhttp://www.sherpa.ac.uk/romeo/issn/0028-0836/ Author can archive pre-print (ie pre-refereeing). On author's personal website, institutional repository and funder designated repository (Sherpa/Romeo as of 24/9/2018).2015-11-2610.1038/nature15747