Twenty years of collaboration from around thirty institutions, including EPFL, have enabled astrophysicists to map the structure of the Universe from its very beginnings.
An international consortium with the participation of EPFL has analyzed several million galaxies and quasars as part of a vast program of cosmological surveys. The result is the largest 3D map of the universe produced to date.
These works are the fruit of the collaboration, over more than twenty years, of several hundred scientists from thirty different institutions around the world, said the Federal Polytechnic School of Lausanne (EPFL) in a press release.
The researchers were brought together in the “Sloan Digital Sky Survey” (SDSS) and around an optical telescope dedicated to the project located in New Mexico, in the United States. The mapping work was released to the public on Sunday in the form of more than 20 scientific publications.
The analyzes come in particular from the last cosmological survey of the SDSS, called “The extended Baryon Oscillation Spectroscopic Survey” (eBOSS), which involves more than 100 astrophysicists. Several EPFL researchers are part of it: Jean-Paul Kneib, who heads the Laboratory of Astrophysics (LASTRO), is even the initiator and was the principal researcher for several years.
“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 which are the galaxies actively forming stars and quasars”, said Jean-Paul Kneib, quoted in the press release.
Dark matter and energy
The finalized map shows filaments of matter and voids which more precisely define the structure of the Universe from its beginnings, that is to say when it was only 380,000 years old. From there, the researchers measured what were the recurring patterns in the distribution of galaxies, thus identifying several key cosmological parameters, such as the density of dark matter and dark energy in the Universe.
To carry out this survey, the teams involved in the eBOSS project looked at different tracers revealing mass distribution in the Universe. 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 galaxies, the blue ones. To go back further, that is to say up to eleven billion years, they used quasars – galaxies whose super-massive black hole, in their center, is made extremely luminous by the matter which is engulfed there.
The history brought to light by this map reveals that at one point the expansion of the Universe accelerated and has since continued to do so. This seems to be due to the presence of dark energy, an invisible element which integrates naturally into Einstein’s general theory of relativity but whose origin is not yet understood.
When eBOSS observations are put into perspective with studies carried out so far in the early days of the Universe, shifts appear in the model in terms of the measurement of the speed of expansion.
The one commonly accepted today, which is called the “Hubble constant”, is 10% slower than the value calculated from the distances between the galaxies closest to ours. However, the high precision and wide variety of data in the eBOSS program makes it unlikely that this difference is due to chance.
To date there is no commonly accepted explanation for these disagreements between the different measures of the speed of expansion, but the fact that a still unknown form of matter or energy from the primordial Universe can having left traces in our history is an interesting possibility, concludes EPFL.
(ATS / NXP)
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