Astrophysicists around the world released the largest 3D map of the Universe ever 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 fruit of a collaboration of more than twenty years of hundreds of scientists from around thirty different institutions around the world, was drawn up from the last 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 microwave 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.
The use of quasars
“However, there was 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), ”said Jean-Paul Kneib, astrophysicist at the Swiss Federal Institute of Technology in 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 further, that is to say up to eleven billion years, they used quasars – galaxies whose supermassive black hole, in their center, is made extremely bright by the matter which is there engulfed.
The difficult measure of the exact speed of the expansion of the Universe
The map shows that at some point the expansion of the Universe accelerated and has continued to do so ever since. 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 with the studies carried out so far on the early days of the Universe, the researchers noted a gap 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 .