Galaxies exchange matter with their external environment thanks to galactic winds. For the first time, the MUSE instrument from the Very Large Telescope has mapped the galactic wind that drives these exchanges between galaxies and nebulae. This discovery led to the detection of some of the Universe’s missing matter.
Because of the galactic winds created by stellar explosions, galaxies can receive and exchange matter with their external environment. An international research team led on the French side by the CNRS and l’Université Claude Bernard Lyon has for the first time mapped a galactic wind using the MUSE instrument from the ESO’s Very Large Telescope. This one-of-a-kind observation, detailed in a study published in MNRAS on September 16, 2021, helped to reveal where some of the Universe’s missing matter is located and to observe the formation of a nebula around a galaxy.
Galaxies are celestial islands of stars and possess ordinary or baryonic matter, which consists of elements from the periodic table, as well as dark matter, whose composition remains unknown. One of the major challenges in understanding the formation of galaxies is that approximately 80% of the baryons that make up the normal matter of galaxies is missing. According to models, they were expelled from galaxies into intergalactic space by the galactic winds created by stellar explosions.
Note: Baryons are particles consisting of three quarks, such as protons and neutrons. They make up atoms and molecules as well as all visible structures in the observable Universe (stars, galaxies, galaxy clusters, etc.). The “missing” baryons, which had never before been observed, must be distinguished from dark matter, which consists of non-baryonic matter of an unknown nature.
An international team led by researchers from the CNRS and l’Université Claude Bernard Lyon successfully used the MUSE instrument to create a detailed map of the galactic wind driving exchanges between a young galaxy in formation and a nebula (a cloud of gas and interstellar dust).
The perfect positioning of the galaxy and the quasar, as well as the discovery of gas exchange due to galactic winds, made it possible to draw up a unique map. This enabled the first observation of a nebula in formation that is simultaneously emitting and absorbing magnesium—some of the Universe’s missing baryons—with the Gal1 galaxy.
This type of normal matter nebula is known in the near Universe, but its existence for young galaxies in formation was only assumed.
Scientists discovered some of the Universe’s missing baryons, confirming that 80–90% of normal matter is found outside of galaxies, an observation that will help expand models for galaxies’ evolution.
Reference: “MusE GAs FLOw and Wind (MEGAFLOW) VIII. Discovery of a Mgii emission halo probed by a quasar sightline” by Johannes Zabl, Nicolas F Bouché, Lutz Wisotzki, Joop Schaye, Floriane Leclercq, Thibault Garel, Martin Wendt, Ilane Schroetter, Sowgat Muzahid, Sebastiano Cantalupo, Thierry Contini, Roland Bacon, Jarle Brinchmann and Johan Richard, 28 July 2021, Monthly Notices of the Royal Astronomical Society.