One of the major problems in understanding the formation of galaxies is that approximately 80% of the baryons that make up the normal matter of galaxies is missing, expelled over eons from galaxies into inter-galactic space by the galactic winds created by stellar explosions.
Mapped for the First Time
A new study 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 can receive and exchange matter with their external environment thanks to the galactic winds created by stellar explosions. Using the MUSE instrument on the Very Large Telescope at the ESO Paranal Observatory (Chile), an international research team, led by the CNRS and l’Université Claude Bernard Lyon 1, mapped a galactic wind for the first time.
One of the major problems in understanding the formation of galaxies–islands of stars in the universe– is that approximately 80% of the baryons that make up the normal, baryonic, matter of galaxies is missing. According to models, they were expelled from galaxies into inter-galactic space by the galactic winds created by stellar explosions.
The international team generated a map of the galactic wind driving exchanges between a young galaxy in formation and a nebula (a cloud of gas and interstellar dust) shown in the image below –Left: Demarcation of the quasar and the galaxy studied here, Gal1. Center: Nebula consisting of magnesium represented with a size scale. Right: superimposition of the nebula and the Gal1 galaxy. ( © Johannes Zabl).
Guided by a Quasar “Lighthouse”
The team chose to observe galaxy Gal1 due to the proximity of a quasar, which served as a “lighthouse” for the scientists by guiding them toward the area of study. They also planned to observe a nebula around this galaxy, although the success of this observation was initially uncertain, as the nebula’s luminosity was unknown.
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.
Missing Mass is Outside of Galaxies
This type of normal matter nebula is known in the near universe, but their existence for young galaxies in formation had only been assumed. Scientists thus discovered some of the universe’s missing baryons, thereby confirming that 80–90% of normal matter is located outside of galaxies. The identification that such a large fraction of galaxies’ mass is located outside their observable, or luminous part, as opposed to within it, will help expand models for the evolution of galaxies.
Using an analogy, Nicolas Bouche, a CNRS astrophysicist working at CRAL (Center of Research in Astrophysique of Lyon}, wrote in an email to The Daily Galaxy about how confirming that 80–90% of normal matter is located outside of galaxies will help expand models for the evolution of galaxies: ”This confirmation is a bit like expecting to have lots of ice around galaxies (`islands in the universe’) and we saw the icebergs with these observations; so this tells us that there must be even more `ice`( missing matter) around galaxies.
“The models of galaxy evolution,” Bouche continued, “ predict that all galaxies should have galactic winds like this one, and our observations put constraints on the wind properties (size, volume, and density with the absorption in the quasar). These properties are related to the type of wind models people use in their numerical simulations. The challenge for models now will be to match our observations in addition to the other constraints on galaxies.”
Source: Johannes Zabl et al, MusE GAs FLOw and Wind (MEGAFLOW) VIII. Discovery of a MgIIii emission halo probed by a quasar sightline, Monthly Notices of the Royal Astronomical Society (2021). DOI: 10.1093/mnras/stab2165
The Daily Galaxy, Avi Shporer, formerly a NASA Sagan Fellow at the Jet Propulsion Laboratory (JPL).currently with the MIT Kavli Institute for Astrophysics and Space Research via CNRS and Nicolas Bouche