Steph Deschamps / July 20, 2020
Astrophysicists around the world on Monday released the largest 3D map of the Universe ever made, resulting from the analysis of more than four million galaxies and quasars, ultraluminous objects emitting colossal energy.
"This work simply gives 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 a collaboration of more than twenty years of hundreds of scientists from 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 on galaxies and distance measurements had also given a good understanding of the expansion of the Universe that has taken place over the past billion years. "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.
Expansion
"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", said Jean-Paul Kneib, astrophysicist at the Federal Polytechnic School of Lausanne (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, researchers observed the oldest and most red galaxies. For more distant eras, they concentrated on the youngest, 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. submerged.
The map shows that at some point the expansion of the Universe accelerated and has since continued to do so. This acceleration seems to be due, according to the researchers, to the presence of dark energy, an invisible element that fits into Einstein's general theory of relativity but whose origin is not yet understood.
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 commonly accepted today, called "Hubble constant", has proven to be 10% slower than the calculated value, detailed the EPFL, noting that there is, to date, no explanation .