![]() We measure the eBOSS quasars between redshift 0.8 and 2.2 for an average redshift of z=1.52. The higher the redshift of an object is, the more the light we capture from that object was emitted long ago. The redshift is of cosmological origin and is a consequence of the expansion of the universe. It gives access to the distance between the quasar and the observer along the line of sight. Quasars correspond to active nuclei of galaxies and the intense light they emit comes from the accretion disk located around the central super massive black hole. On the figure opposite, a spectrum of quasars is represented containing several lines corresponding to emission lines from the heated gas during the accretion process. The position of these lines is shifted towards the long wavelengths, we speak of spectral redshift. It has allowed astronomers to accurately measure the position of more than 148,000 quasars and to reconstruct the largest map of the spatial distributions of today's large structures more than 10 billion years old ( see June 2017 Highlight). The 2.5-meter-diameter SDSS telescope located at the Apache Point Observatory in New Mexico (USA) and connected to the eBOSS multi-spectrograph, has been observing an unprecedented number of quasars since 2014. Using eBOSS Quasars to probe an unexplored era DPhP cosmologists are heavily involved in all stages of the eBOSS program, as well as in its successor, the DESI project located at the Kitt Peak National Observatory in Arizona, which is scheduled to begin data collection in 2020. The collaboration continues to acquire data with final analysis planned for the end of 2019, which will double the sample size. The results were published in the Monthly Notices of the Royal Astronomical Society ( P. The measurements made confirm the validity of the model of cosmology based on general relativity and can also be used to constrain alternative theories of gravity. The sample on which the analysis is based corresponds to 2 years of data collection and has already allowed the selection of more than 148,000 quasars. Quasars are among the brightest sources of light in the Universe and allow us to probe an era almost unexplored by this cosmological test, when the Universe was between 3 and 7 billion years old. It allows to test directly the gravitation theory at the scale of these large structures.įor the first time, the eBOSS multi-spectrograph mounted on the Sloan Digital Sky Survey telescope in New Mexico, allowed to measure this parameter from the distribution of spatial correlations of quasars. This cosmological parameter is called the growth rate of cosmic structures. The current model of cosmology is based on general relativity as a theory of gravitation and establishes a theoretical prediction for the quantity of galaxies that form at a given period of the Universe. More than twenty years after the discovery of the acceleration of the expansion of the Universe, the nature of the physical phenomenon at the origin of this acceleration, called "dark energy", is still unknown.
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