In astrophysics, it means looking far into the past. Scientists then study the distant universe to understand its evolution, from its beginnings to the present day. That’s what several teams of scientists have done by discovering a superstructure dating back to the youth of the universe when it was only about three billion years old. Also called the “proto-cluster”, this superstructure, which contains thousands of galaxies, will in the future become a cluster of galaxies, such as the Virgo cluster, in which our galaxy is located.
“We observe this proto-cluster as it was when the universe was about 3 billion years old. Began to fall, and today very few stars are formed in the galaxies of the near universe”, explain to Science and the Future Hervé Dole, astrophysicist at the Institute of Space Astrophysics or IAS (CNRS / Paris-Saclay University).
Discovered more than ten years ago thanks to the European Planck satellite, its presence has only recently been confirmed thanks to several additional studies. Several international teams have scrutinized it in detail in two studies published in journals Monthly announcements from the Royal Astronomical Society in March 2021 and Astronomy and astrophysics in October 2021.
From 2009 to today, a shining point that has become a proto-cluster
In astrophysics, it means looking far into the past. Scientists then study the distant universe to understand its evolution, from its beginnings to the present day. That’s what several teams of scientists have done by discovering a superstructure dating back to the youth of the universe when it was only about three billion years old. Also called the “proto-cluster”, this superstructure, which contains thousands of galaxies, will in the future become a cluster of galaxies, such as the Virgo cluster, in which our galaxy is located.
“We observe this proto-cluster as it was when the universe was about 3 billion years old. Began to fall, and today very few stars are formed in the galaxies of the near universe”, explain to Science and the Future Hervé Dole, astrophysicist at the Institute of Space Astrophysics or IAS (CNRS / Paris-Saclay University).
Discovered more than ten years ago thanks to the European Planck satellite, its presence has only recently been confirmed thanks to several additional studies. Several international teams have scrutinized it in detail in two studies published in journals Monthly announcements from the Royal Astronomical Society in March 2021 and Astronomy and astrophysics in October 2021.
From 2009 to today, a shining point that has become a proto-cluster
It was thanks to data collected by the Planck satellite, developed by the European Space Agency (ESA), and launched in May 2009 to study the youth of the universe, that this proto-cluster was discovered. In operation until 2012, but with results still published today, it made it particularly possible with extreme precision to map the cosmic microwave background, the first light in the universe emitted only 380,000 years after the Big Bang.
“It all started in 2009 with the observations made by Planck. Thanks to his data, we have identified 2,000 potential galaxy structures. Planck has a low sensitivity to point sources because it is designed and optimized to study the cosmic background. So if he observes a point of light , it’s really very bright. ” explains Hervé Dole, who participated in the preparation of the two studies.
Later, spectroscopy managed the rest. This technique makes it possible to decompose the light that reaches us, to emit the object that is at its origin and its distance, as Hervé Dole explains. “Among all the wavelengths that could be observed, some in particular correspond to the emission of dust from galaxies heated by young stars in formation, in the order of one hundred microns (one micron equals one millionth of a meter). To locate a galaxy, therefore, it is necessary to find a very bright point corresponding to this emission peak. Then it was left to distinguish what was a possible cluster of galaxies from what were in fact several galaxies distant from each other but randomly aligned on our images. Only spectroscopy makes it possible to answer it, because it makes it possible to assess at what distance is the object being observed. Then we identified two substructures, two proto-clusters, which in billions of years will turn into a giant cluster resembling the Virgin Cluster “.
A question for current models for the formation of superheaps of galaxies
Named PHz G237.01 + 42.50 or G237 for short, this gigantic astrophysical structure will in future evolve into a supercluster of galaxies once the proto-clusters that make it up have come together by gravity to the point where they merge. . According to predictions, its final mass will reach more than 5.1014 solar masses or 500 million million solar masses! A gigantic mass comparable to the cluster in which our galaxy is located, the Virgin Cluster. Composed of thousands of galaxies, hot gases and dark matter, these clusters represent the largest observable structures in the universe. Understanding how they behave enables scientists to perfect current cosmological models.
But the rate of star formation measured in the galaxies that make up G237 by Hervé Dole’s team reaches values far too high to match the current description of the formation of superheaps of galaxies at a rate of several thousand solar masses per year. “In galaxies, there are two main sources of light energy: star formation and the supermassive black hole that sits in the middle, in the case of active galaxies. This is the star formation we used. The molecular clouds in which stars are formed emit in the infrared. The more active the star formation, the more intense the light signal is measured. That’s how we were able to calculate a very high star formation rate. “explains Hervé Dole.
Current models are based on data that are inherently incomplete because such astrophysical objects are quite difficult to observe, and this could well help to improve them, as Hervé Dole explains. “Our discovery does not call into question the standard cosmological model that describes the evolution of the universe since the Big Bang. On the other hand, in this model there are many features, especially in the way galaxies are formed. It is this part that our study questions. For the rest, we will have to tune the models of the simulators so that they take into account our last measurement. The forthcoming launch of the James Webb Space Telescope and the European Euclid Project should make it possible to find other similar G237 objects and thus provide more answers to the formation of galaxies “, hopes the researcher.