William J. Chaplin, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK, Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA, USA 0000-0002-5714-8618
,
Aldo M. Serenelli, Institut d'Estudis Espacials de Catalunya, Barcelona, Spain 0000-0001-6359-2769
,
Andrea Miglio, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK
,
Thierry Morel, Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Liège, Belgium
,
J. Ted Mackereth, Aarhus Universitet
,
Fiorenzo Vincenzo, Department of Physics, The Ohio State University, Columbus, OH, USA 0000-0002-0743-9994
Orlagh Creevey, Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France 0000-0003-1853-6631
,
Rafael A. García, AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, F-91191 Gif-sur-Yvette, France 0000-0002-8854-3776
Keivan G. Stassun, Vanderbilt Initiative in Data-intensive Astrophysics (VIDA), 6301 Stevenson Center Lane, Nashville, TN 37235, USA 0000-0002-3481-9052
,
Michäel Bazot, Center for Space Science, NYUAD Institute, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
,
Paul G. Beck, Departamento de Astrofísica, Universidad de La Laguna, E-28207 La Laguna, Tenerife, Spain
,
Keaton J. Bell, Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany, DIRAC Institute, Department of Astronomy, University of Washington, Seattle, WA 98195-1580, USA
,
Maria Bergemann, Max Planck Institute for Astronomy, Heidelberg, Germany 0000-0002-9908-5571
,
Derek L. Buzasi, Dept. of Chemistry and Physics, Florida Gulf Coast University, 10501 FGCU Boulevard South, Fort Myers, FL 33965, USA
,
Othman Benomar, Solar Science Observatory, NAOJ and Department of Astronomical Science, Sokendai (GUAS), Mitaka, Tokyo, Japan
,
Diego Bossini, Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
,
Lisa Bugnet, AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, F-91191 Gif-sur-Yvette, France 0000-0003-0142-4000
,
Tiago L. Campante, Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, s/n, PT4169-007 Porto, Portugal 0000-0002-4588-5389
,
Zeynep çelik Orhan, Department of Astronomy and Space Sciences, Ege University, İzmir, Turkey 0000-0002-9424-2339
,
Enrico Corsaro, INAF—Osservatorio Astrofisico di Catania, via S. Sofia 78, I-95123, Catania, Italy 0000-0001-8835-2075
,
Lucía González-Cuesta, Departamento de Astrofísica, Universidad de La Laguna, E-28207 La Laguna, Tenerife, Spain
,
Guy R. Davies, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK
,
Maria Pia Di Mauro, INAF-IAPS, Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, I-00133 Roma, Italy 0000-0001-7801-7484
,
Ricky Egeland, High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, USA 0000-0002-4996-0753
,
Yvonne P. Elsworth, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK, Aarhus Universitet
,
Patrick Gaulme, Department of Astronomy, New Mexico State University, Las Cruces, NM 88003, USA 0000-0001-9984-0891
,
Hamed Ghasemi, Department of Physics, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
,
Zhao Guo, Pennsylvania State University
,
Oliver J. Hall, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK, Aarhus Universitet
,
Amir Hasanzadeh, Department of Physics, University of Zanjan, Zanjan, Iran
Savita Mathur, Departamento de Astrofísica, Universidad de La Laguna, E-28207 La Laguna, Tenerife, Spain
,
Josefina Montalbán, Aarhus Universitet
,
Benoit Mosser, LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France 0000-0002-7547-1208
,
Andres Moya Bedón, Aarhus Universitet
,
Martin Bo Nielsen, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK, Aarhus Universitet, Center for Space Science, NYUAD Institute, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
,
Sibel Örtel, Department of Astronomy and Space Sciences, Ege University, Bornova, 35100 Izmir, Turkey
,
Ben M. Rendle, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK, Aarhus Universitet
,
George R. Ricker, Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
,
Thaíse S. Rodrigues, INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padua, Italy aparicio@iac.es
,
Ian W. Roxburgh, Astronomy Unit, Queen Mary, University of London, Mile End Road, London, E1 4NS, UK
,
Hossein Safari, Department of Physics, University of Zanjan, Zanjan, Iran 0000-0003-2326-3201
,
Mathew Schofield, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK, Aarhus Universitet
,
Sara Seager, Department of Aeronautics and Astronautics, MIT, Cambridge, MA, USA
,
Barry Smalley, Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG, UK 0000-0002-3456-087X
Róbert Szabó, MTA CSFK Lendület Near-Field Cosmology Research Group, Budapest, Hungary
,
Jamie Tayar, Hubble Fellow, Institute for Astronomy, University of Hawai`i, Honolulu, HI, USA
,
Nathalie Themeßl, Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany
,
Alexandra E. L. Thomas, Aarhus Universitet
,
Roland K. Vanderspek, Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
,
Walter E. van Rossem, Aarhus Universitet
,
Mathieu Vrard, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre 687, 4169-007, Porto, Portugal
,
Achim Weiss, Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching bei München, Germany
,
Timothy R. White, Aarhus Universitet, Australian National University
,
Joshua N. Winn, Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA 0000-0002-4265-047X
,
Mutlu Yıldız, Department of Astronomy and Space Sciences, Ege University, İzmir, Turkey 0000-0002-7772-7641
Over the course of its history, the Milky Way has ingested multiple
smaller satellite galaxies1. Although these accreted stellar
populations can be forensically identified as kinematically distinct
structures within the Galaxy, it is difficult in general to date
precisely the age at which any one merger occurred. Recent results have
revealed a population of stars that were accreted via the collision of a
dwarf galaxy, called Gaia-Enceladus1, leading to substantial
pollution of the chemical and dynamical properties of the Milky Way.
Here we identify the very bright, naked-eye star ν Indi as an
indicator of the age of the early in situ population of the Galaxy. We
combine asteroseismic, spectroscopic, astrometric and kinematic
observations to show that this metal-poor, alpha-element-rich star was
an indigenous member of the halo, and we measure its age to be 11.0
±0.7 ? (stat) ±0.8 ? (sys) billion years. The star bears
hallmarks consistent with having been kinematically heated by the
Gaia-Enceladus collision. Its age implies that the earliest the merger
could have begun was 11.6 and 13.2 billion years ago, at 68% and 95%
confidence, respectively. Computations based on hierarchical
cosmological models slightly reduce the above limits.