2023-09-08 02:19:28
Astronomers have discovered for the first time a ‘bubble of galaxies’, a structure of colossal size whose genesis dates back to the earliest times of the Universe, some 13.8 billion years ago, according to a study in Astrophysical journal .
It is necessary to imagine, for lack of being able to observe it with the naked eye, a structure of a billion light-years in diameter, ten thousand times larger than our galaxy.
Located in what astronomers call the Near Universe, about 820 million light-years from the Milky Way, it can be described as a “spherical shell with a heart”, French researcher Daniel Pomarède told AFP. , astrophysicist at the Atomic Energy Commission (CEA) and co-author of the study published this week.
The heart of this shell is the Bouvier supercluster of galaxies, surrounded by a great void, and girdled by other superclusters and galactic filaments such as Sloan’s Great Wall.
His discovery “is part of a very long scientific process”, according to Mr. Pomarède, because it validates a phenomenon described in 1970 by the American cosmologist and future Nobel Prize in physics, Jim Peebles.
He postulates that in the primordial Universe, then made up of a plasma of particles and light, the processes at work produce acoustic waves. These vibrations will create within the plasma some kind of bubbles with matter in the center.
The process stops 380,000 years after the Big Bang, “freezing” the shape of these bubbles. They will then grow in size following the expansion of the Universe, like so many “fossils” of its first ages.
The phenomenon, bearing the barbaric name of baryonic acoustic oscillation (BAO), had found indirect proof of its existence in 2005, with statistical analyzes on catalogs of galaxies.
– “Whispers of awakening” –
Until the discovery of Ho’oleilana, a word taken from the Hawaiian song of creation meaning “whispers of awakening”. This name owes a lot to the study’s first author, Richard Brent Tully, an American astrophysicist from the Honolulu Institute of Astronomy.
We already owed him the discovery in 2014, with Daniel Pomarède, of the galactic super-cluster Laniakea, “huge sky” in Hawaiian, which alone contains some 100,000 galaxies, including our Milky Way.
The discovery of Ho’oleilana was made by chance, through Mr. Tully’s work on new catalogs of galaxies. “It was something unexpected”, according to Mr. Pomarède, then asked for a cartography of this region of the sky “which was a bit of terra incognita for us”.
The two researchers then called on the young Australian cosmologist Cullan Howlett, from the University of Brisbane. This third author of the study, an expert in BAO and in the analysis of large catalogs of galaxies, “mathematically determined the spherical structure that best corresponded to the data provided”.
The whole made it possible to visualize in three dimensions the shape of Ho’oleilana and the position of the archipelagos of galaxies which compose it.
“Icing on the cake”, according to the CEA researcher, this work contributes to a key subject of cosmology, the value of the Hubble constant. The latter makes it possible to calculate the rate of expansion of the Universe, which sees its galaxies continue to move away from each other, and a bubble like Ho’oleilana continue to inflate.
But this Hubble constant is subject to a “tension”, that is to say to different values depending on whether it is measured in the near or distant Universe. In this case, the work on Ho’oleilana confirms the first.
The adventure of discovering other bubbles has only just begun, with for example the arrival of instruments such as the European space telescope Euclid, launched in July, which will help to understand the expansion of the Universe. Or that to come from the large South African SKA radio telescope, “to observe the Universe from the southern side of our galaxy”, concludes Mr. Pomarède.
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