Artist’s impression of a dusty starburst galaxy
The Tarantula Nebula in the Large Magellanic Cloud
Artist’s impression of a starburst galaxy
Videos
ESOcast 163 Light: Too Many Massive Stars in Starburst Galaxies (4K UHD)
Artist’s impression of distant starburst galaxy
Astronomers using ALMA and the VLT have
discovered that both starburst galaxies in the early Universe and a
star-forming region in a nearby galaxy contain a much higher proportion
of massive stars than is found in more peaceful galaxies. These findings
challenge current ideas about how galaxies evolved, changing our
understanding of cosmic star-formation history and the build up of
chemical elements.
Probing the distant Universe a team of scientists, led by University of Edinburgh astronomer Zhi-Yu Zhang, used the Atacama Large Millimeter/submillimeter Array (ALMA) to investigate the proportion of massive stars in four distant gas-rich starburst galaxies [1].
These galaxies are seen when the Universe was much younger than it is
now so the infant galaxies are unlikely to have undergone many previous
episodes of star formation, which might otherwise have confused the
results.
Zhang and his team developed a new technique — analogous to radiocarbon dating (also known as carbon-14 dating) — to measure the abundances of different types of carbon monoxide in four very distant, dust-shrouded starburst galaxies [2]. They observed the ratio of two types of carbon monoxide containing different isotopes [3].
“Carbon and oxygen isotopes have different origins”, explains Zhang. “18O is produced more in massive stars, and 13C is produced more in low- to intermediate-mass stars.”
Thanks to the new technique the team was able to peer through the dust
in these galaxies and assess for the first time the masses of their
stars.
The mass of a star is the most important factor determining
how it will evolve. Massive stars shine brilliantly and have short
lives and less massive ones, such as the Sun, shine more modestly for
billions of years. Knowing the proportions of stars of different masses
that are formed in galaxies therefore underpins astronomers’
understanding of the formation and evolution of galaxies throughout the
history of the Universe. Consequently, it gives us crucial insights
about the chemical elements available to form new stars and planets
and, ultimately, the number of seed black holes that may coalesce to
form the supermassive black holes that we see in the centres of many
galaxies.
Co-author Donatella Romano from the INAF - Astrophysics and Space Science Observatory in Bologna explains what the team found: “The ratio of 18O to 13C
was about 10 times higher in these starburst galaxies in the early
Universe than it is in galaxies such as the Milky Way, meaning that
there is a much higher proportion of massive stars within these
starburst galaxies.”
The ALMA finding is consistent with another discovery in the local Universe. A team led by Fabian Schneider of the University of Oxford, UK, made spectroscopic measurements with ESO’s Very Large Telescope of 800 stars in the gigantic star-forming region 30 Doradus in the Large Magellanic Cloud in order to investigate the overall distribution of stellar ages and initial masses [4].
Schneider explained, “We found around 30% more stars
with masses more than 30 times that of the Sun than expected, and about
70% more than expected above 60 solar masses. Our results challenge the
previously predicted 150 solar mass limit for the maximum birth mass of
stars and even suggest that stars could have birth masses up to 300
solar masses!”
Rob Ivison, co-author of the new ALMA paper, concludes:
“Our findings lead us to question our understanding of cosmic history.
Astronomers building models of the Universe must now go back to the
drawing board, with yet more sophistication required.”
Notes
[1] Starburst galaxies are galaxies that are undergoing an
episode of very intense star formation. The rate at which they form new
stars can be 100 times or more the rate in our own galaxy, the Milky
Way. Massive stars in these galaxies produce ionising radiation, stellar outflows, and supernova explosions,
which significantly influence the dynamical and chemical evolution of
the medium around them. Studying the mass distribution of stars in these
galaxies can tell us more about their own evolution, and also the
evolution of the Universe more generally.
[2] The radiocarbon dating
method is used for determining the age of an object containing organic
material. By measuring the amount of 14C, which is a
radioactive isotope whose abundance continuously decreases, one can
calculate when the animal or plant died. The isotopes used in the ALMA
study, 13C and 18O, are stable and their abundances continuously increase during the lifetime of a galaxy, being synthesised by thermal nuclear fusion reactions inside stars.
[3] These different forms of
the molecule are called isotopologues and they differ in the number of
neutrons they can have. The carbon monoxide molecules used in this study
are an example of such molecular species, because a stable carbon
isotope can have either 12 or 13 nucleons in its nucleus, and a stable oxygen isotope can have either 16, 17, or 18 nucleons.
[4] Schneider et al. made spectroscopic observations of individual stars in 30 Doradus, a star-forming region in the nearby Large Magellanic Cloud, using the Fibre Large Array Multi Element Spectrograph (FLAMES) on the Very Large Telescope (VLT).
This study was one of the first to be carried out that has been
detailed enough to show that the Universe is able to produce
star-forming regions with different mass distributions from that in the
Milky Way.
More Information
The ALMA results are published in a paper entitled “Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time” that will appear in Nature on 4 June 2018. The VLT results are published in a paper entitled “An excess of massive stars in the local 30 Doradus starburst”, which has been published in Science on 5 January 2018.
The ALMA team is composed of: Z. Zhang (Institute for Astronomy, University of Edinburgh, Edinburgh, UK; European Southern Observatory, Garching bei München, Germany), D. Romano (INAF, Astrophysics and Space Science Observatory, Bologna, Italy), R. J. Ivison (European Southern Observatory, Garching bei München, Germany; Institute for Astronomy, University of Edinburgh, Edinburgh, UK), P .P. Papadopoulos (Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece; Research Center for Astronomy, Academy of Athens, Athens, Greece;) and F. Matteucci (Trieste University; INAF, Osservatorio Astronomico di Trieste; INFN, Sezione di Trieste, Trieste, Italy)
The VLT team is composed of: F. R. N. Schneider ( Department of Physics, University of Oxford, UK), H. Sana (Institute of Astrophysics, KU Leuven, Belgium), C. J. Evans ( UK Astronomy Technology Centre, Royal Observatory Edinburgh, Edinburgh, UK), J. M. Bestenlehner (Max-Planck-Institut für Astronomie, Heidelberg, Germany; Department of Physics and Astronomy, University of Sheffield, UK), N. Castro (Department of Astronomy, University of Michigan, USA), L. Fossati (Austrian Academy of Sciences, Space Research Institute, Graz, Austria), G. Gräfener (Argelander-Institut für Astronomie der Universität Bonn, Germany), N. Langer (Argelander-Institut für Astronomie der Universität Bonn, Germany), O. H. Ramírez-Agudelo (UK Astronomy Technology Centre, Royal Observatory Edinburgh, Edinburgh, UK), C. Sabín-Sanjulián (Departamento de Física y Astronomía, Universidad de La Serena, Chile), S. Simón-Díaz (Instituto de Astrofísica de Canarias, Tenerife, Spain; Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain), F. Tramper (European Space Astronomy Centre, Madrid, Spain), P. A. Crowther (Department of Physics and Astronomy, University of Sheffield, UK), A. de Koter (Astronomical Institute Anton Pannekoek, Amsterdam University, Netherlands; Institute of Astrophysics, KU Leuven, Belgium), S. E. de Mink (Astronomical Institute Anton Pannekoek, Amsterdam University, Netherlands), P. L. Dufton (Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Northern Ireland, UK), M. Garcia (Centro de Astrobiología, CSIC-INTA, Madrid, Spain), M. Gieles (Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, UK), V. Hénault-Brunet (National Research Council, Herzberg Astronomy and Astrophysics, Canada; Department of Astrophysics/Institute for Mathematics, Astrophysics and Particle Physics, Radboud University, Netherlands), A. Herrero (Departamento de Física y Astronomía, Universidad de La Serena, Chile), R. G. Izzard (Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, UK; Institute of Astronomy, The Observatories, Cambridge, UK), V. Kalari (Departamento de Astronomía, Universidad de Chile, Santiago, Chile), D. J. Lennon (European Space Astronomy Centre, Madrid, Spain), J. Maíz Apellániz (Centro de Astrobiología, CSIC–INTA, European Space Astronomy Centre campus, Villanueva de la Cañada, Spain), N. Markova (Institute of Astronomy with National Astronomical Observatory, Bulgarian Academy of Sciences, Smolyan, Bulgaria), F. Najarro (Centro de Astrobiología, CSIC-INTA, Madrid, Spain), Ph. Podsiadlowski (Department of Physics, University of Oxford, UK; Argelander-Institut für Astronomie der Universität Bonn, Germany), J. Puls (Ludwig-Maximilians-Universität München, Germany), W. D. Taylor (UK Astronomy Technology Centre, Royal Observatory Edinburgh, Edinburgh, UK), J. Th. van Loon (Lennard-Jones Laboratories, Keele University, Staffordshire, UK), J. S. Vink (Armagh Observatory, Northern Ireland, UK) and C. Norman (Johns Hopkins University, Baltimore, USA; Space Telescope Science Institute, Baltimore, USA)
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 15 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a strategic partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.
Links
Contacts
Zhi-Yu Zhang
University of Edinburgh and ESO
Garching bei München, Germany
Tel: +49-89-3200-6910
Email: zzhang@eso.org
Fabian Schneider
Department of Physics — University of Oxford
Oxford, United Kingdom
Tel: +44-1865-283697
Email: fabian.schneider@physics.ox.ac.uk
Rob Ivison
ESO
Garching bei München, Germany
Tel: +49-89-3200-6669
Email: rob.ivison@eso.org
Mariya Lyubenova
ESO Outreach Astronomer
Garching bei München, Germany
Tel: +49 89 3200 6188
Email: mlyubeno@eso.org
Source: ESO/News
