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July 20, 2020
The fruit of a collaboration of more than twenty years and of hundreds of scientists from around thirty institutions including EPFL, a representation of the universe also shows it in the history of its expansion.
Image above: An image transmitted by the Federal Polytechnic of Lausanne, Sunday July 19. Image Credit: EPFL.
Astrophysicists around the world released the largest 3D map of the Universe on Monday. "This work simply offers us the most complete history of the expansion of the Universe to date," said one of the researchers, Will Percival, of the University of Waterloo.
The map, the result of more than twenty years of collaboration between hundreds of scientists from around thirty different institutions around the world, was drawn up from the latest cosmological survey of the SDSS (Sloan Digital Sky Survey), named “The extended Baryon Oscillation Spectroscopic Survey” (eBOSS), around a telescope located in New Mexico, United States.
Thanks to the numerous theoretical works carried out over time on the Big Bang, as well as to the observation of the cosmic diffuse background (a weak light radiation left by the Big Bang), the first moments of the Universe are relatively well known to researchers. Studies of galaxies and distance measurements had also given a good understanding of the expansion of the Universe that has occurred over the last billion years.
Image above: A chronology of the universe visualized by researchers, image of the NSF, the American national fund for science. Image Credit: NSF.
The use of quasars
"However, there was still a lack of data between the beginning of the Universe and the current period," said Kyle Dawson, of the University of Utah and one of the leaders of the project.
“In 2012, I launched the eBOSS project with the idea of producing the most complete 3D mapping of the Universe, using for the first time new tracers such as galaxies actively forming stars and quasars (objects ultraluminous emitting colossal energy) ”, indicated Jean-Paul Kneib, astrophysicist at the Federal Polytechnic School of Lausanne (EPFL).
Earth and solar constellations on the 3D map. Image Credit: EPFL.
The map shows filaments of matter and voids defining the structure of the Universe from its beginnings, when it was only 380,000 years old. For the part of the map relating to the Universe six billion years ago in the past, the researchers observed the oldest and reddest galaxies. For more distant eras, they have focused on the younger, blue galaxies.
To go back as far as possible, that is to say up to eleven billion years ago, they used quasars - galaxies whose supermassive black hole, at their center, is made extremely luminous by the matter therein. engulfed.
The difficult measure of the exact speed of the Universe's expansion
The map shows that at some point the expansion of the Universe accelerated and has since continued to do so. According to the researchers, this acceleration seems to be due to the presence of dark energy, an invisible element which integrates into Einstein's general theory of relativity but whose origin is not yet understood.
Astrophysicists fill gaps in the history of the Universe
Astrophysicists have known for several years that the universe is expanding, but they have since tried to measure the exact speed of this expansion.
By comparing the observations made by the eBOSS program to studies conducted so far in the early days of the Universe, the researchers found a discrepancy between the speeds.
The one currently accepted, called the "Hubble constant", has turned out to be 10% slower than the calculated value, detailed the EPFL, noting that there is, to date, no explanation.
Related links:
eBOSS: https://www.sdss.org/surveys/eboss/
Ecole polytechnique fédérale de Lausanne (EPFL): https://www.epfl.ch/en/
EPFL Press Release: https://actu.epfl.ch/news/astrophysicists-fill-gaps-in-the-history-of-the-un/
Images (mentioned), Video (EPFL), Text, Credits: AFP/EPFL/Orbiter.ch Aerospace/Roland Berga.
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