Part of the missing matter of the universe found

Galaxies can receive and exchange matter with their external environment thanks to galactic winds created by stellar explosions. Using the MUSE instrument of ESO’s Very Large Telescope, an international research team, led on the French side by the CNRS and the University Claude Bernard Lyon 1, mapped a galactic wind for the first time. This unique finding, detailed in a study published in MNRAS on September 16, 2021, revealed where some of the universe’s missing matter is located and observed the formation of a nebula around a galaxy.

Galaxies are like islands of stars in the universe and have ordinary matter, or baryon, made up of elements from the periodic table, as well as dark matter, the composition of which remains unknown. One of the major problems in understanding the formation of galaxies is that about 80% of the baryons that make up the normal matter of galaxies are missing. According to the models, they were forced out of galaxies into intergalactic space by galactic winds created by stellar explosions.

An international team led on the French side by researchers from the CNRS and the University Claude Bernard Lyon successfully used the MUSE instrument to generate a detailed map of the galactic wind leading to exchanges between a young galaxy in formation and a nebula (a cloud gas and interstellar dust).

The team chose to observe the galaxy Gal1 because of the proximity of a quasar, which served as a “beacon” for scientists by guiding them to the study area. They also planned to observe a nebula around this galaxy, although the success of this observation was initially uncertain, as the luminosity of the nebula was unknown.

The perfect positioning of the galaxy and the quasar, as well as the discovery of gas exchanges due to galactic winds, made it possible to draw a unique map. This enabled the first observation of a forming nebula that simultaneously emits and absorbs magnesium – some of the universe’s missing baryons – with the galaxy Gal1.

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 have thus discovered some of the missing baryons in the universe, confirming that 80 to 90% of normal matter is found outside the galaxies, an observation that will expand models of galaxy evolution.