Part of the Universe’s Missing Matter Found Thanks to the MUSE Instrument (Cosmology)

  • Galaxies exchange matter with their external environment thanks to galactic winds.
  • The MUSE instrument from the Very Large Telescope has, for the very first time, mapped the galactic wind that drive these exchanges between galaxies and nebulae.
  • This observation led to the detection of some of the Universe’s missing matter.

Galaxies can receive and exchange matter with their external environment thanks to the galactic winds created by stellar explosions. Thanks to the MUSE instrument1 from the Very Large Telescope at the ESO, an international research team, led on the French side by the CNRS and l’Université Claude Bernard Lyon 12, has mapped a galactic wind for the first time. This unique observation, which is detailed in a study published in MNRAS on 16 September 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 like islands of stars in the Universe, 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 problems in understanding the formation of galaxies is that approximately 80% of the baryons3 that make up the normal 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.  

An international team4, led on the French side by researchers from the CNRS and l’Université Claude Bernard Lyon 1, successfully used the MUSE instrument to generate 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 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.

This type of normal matter nebula is known in the near Universe, but their existence for young galaxies in formation had only been supposed.

Scientists thus discovered some of the Universe’s missing baryons, thereby confirming that 80–90% of normal matter is located outside of galaxies, an observation that will help expand models for the evolution of galaxies.

Featured image: Observation of a part of the Universe thanks to MUSE
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


Bibliography

MusE GAs FLOw and Wind (MEGAFLOW) – VIII. Discovery of a Mg II emission halo probed by a quasar sightline. 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. MNRAS, 16 September 2021. https://doi.org/10.1093/mnras/stab2165


Provided by CNRS

Astronomers Solve 900-year-old Cosmic Mystery Surrounding Chinese Supernova Of 1181AD (Cosmology)

A 900-year-old cosmic mystery surrounding the origins of a famous supernova first spotted over China in 1181AD has finally been solved, according to an international team of astronomers.

New research published today (September 15, 2021) says that a faint, fast expanding cloud (or nebula), called Pa30, surrounding one of the hottest stars in the Milky Way, known as Parker’s Star, fits the profile, location and age of the historic supernova.

There have only been five bright supernovae in the Milky Way in the last millennium (starting in 1006). Of these, the Chinese supernova, which is also known as the ‘Chinese Guest Star’ of 1181AD has remained a mystery. It was originally seen and documented by Chinese and Japanese astronomers in the 12th century who said it was as bright as the planet Saturn and remained visible for six months. They also recorded an approximate location in the sky of the sighting, but no confirmed remnant of the explosion has even been identified by modern astronomers. The other four supernovae are all now well known to modern day science and include the famous Crab nebula.

The source of this 12th century explosion remained a mystery until this latest discovery made by a team of international astronomers from Hong Kong, the UK, Spain, Hungary and France, including Professor Albert Zijlstra from The University of Manchester. In the new paper, the astronomers found that the Pa 30 nebula is expanding at an extreme velocity of more than 1,100 km per second (at this speed, traveling from the Earth to the Moon would take only 5 minutes). They use this velocity to derive an age at around 1,000 years, which would coincide with the events of 1181AD.

 Prof Albert Zijlstra, Professor in Astrophysics at Jodrell Bank

The historical reports place the guest star between two Chinese constellations, Chuanshe and Huagai. Parker’s Star fits the position well. That means both the age and location fit with the events of 1181

— Prof Albert Zijlstra, Professor in Astrophysics at Jodrell Bank„

Prof Zijlstra (Professor in Astrophysics at the University of Manchester) explains: “The historical reports place the guest star between two Chinese constellations, Chuanshe and Huagai. Parker’s Star fits the position well. That means both the age and location fit with the events of 1181.”

Pa 30 and Parker’s Star have previously been proposed as the result of a merger of two White Dwarfs. Such events are thought to lead to a rare and relatively faint type of supernova, called a ‘Type Iax supernova’.

Prof Zijlstra added: “Only around 10% of supernovae are of this type and they are not well understood. The fact that SN1181 was faint but faded very slowly fits this type. It is the only such event where we can study both the remnant nebula and the merged star, and also have a description of the explosion itself.”

The merging of remnant stars, white dwarfs and neutron stars, give rise to extreme nuclear reactions and form heavy, highly neutron-rich elements such as gold and platinum. Prof. Zijlstra said: “Combining all this information such as the age, location, event brightness and historically recorded 185-day duration, indicates that Parker’s star and Pa30 are the counterparts of SN 1181. This is the only Type Iax supernova where detailed studies of the remnant star and nebula are possible. It is nice to be able to solve both a historical and an astronomical mystery.”

Paper: The Remnant and Origin of the Historical Supernova 1181 AD – Andreas Ritter1,2, Quentin A. Parker1,2, Foteini Lykou1,2,3, Albert A. Zijlstra2,4, Martín A. Guerrero5, and Pascal Le D6 Published 2021 September 15 • © 2021. The Author(s). Published by the American Astronomical Society. The Astrophysical Journal LettersVolume 918Number 2 – https://iopscience.iop.org/article/10.3847/2041-8213/ac2253 


Provided by University of Manchester