Copyright © 2020, Oxford University PressMarques Chaves, R.Álvarez Márquez, J.Colina, L.Pérez Fournon, I.Schaerer, D.Dalla Vecchia, C.Hashimoto, T.Jiménez Ángel, C.Shu, Y.Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-07372021-04-122021-04-122020-09-16Monthly Notices of the Royal Astronomical Society: Letters 499(1): L105–L110(2020)1745-3925https://academic.oup.com/mnrasl/article/499/1/L105/5906557http://hdl.handle.net/20.500.12666/238We report the discovery of BOSS-EUVLG1 at z = 2.469, by far the most luminous, almost un-obscured star-forming galaxy known at any redshift. First classified as a QSO within the Baryon Oscillation Spectroscopic Survey, follow-up observations with the Gran Telescopio Canarias reveal that its large luminosity, M-UV similar or equal to -24.40 and log(L-Ly alpha/erg s(-1)) similar or equal to 44.0, is due to an intense burst of star formation, and not to an active galactic nucleus or gravitational lensing. BOSS-EUVLG1 is a compact (r(eff) similar or equal to 1.2 kpc), young (4-5 Myr) starburst with a stellar mass log(M-*/M-circle dot) = 10.0 +/- 0.1 and a prodigious star formation rate of similar or equal to 1000 M-circle dot yr(-1). However, it is metal- and dust-poor [12+ log(O/H) = 8.13 +/- 0.19, E(B - V) similar or equal to 0.07, log(L-IR/L-UV) < -1.2], indicating that we are witnessing the very early phase of an intense starburst that has had no time to enrich the ISM. BOSS-EUVLG1 might represent a short-lived (<100 Myr), yet important phase of star-forming galaxies at high redshift that has been missed in previous surveys. Within a galaxy evolutionary scheme, BOSS-EUVLG1 could likely represent the very initial phases in the evolution of massive quiescent galaxies, even before the dusty star-forming phase.engGalaxies: formationGalaxies: high redshiftinfo:eu-repo/semantics/article10.1093/mnrasl/slaa1601745-3933http://dx.doi.org/10.13039/501100011033http://dx.doi.org/10.13039/501100003329info:eu-repo/semantics/restrictedAccess