No need to Mind the Gap: Astrophysicists fill in 11 billion years of our universe’s expansion history

Today, 20th July 2020, the Sloan Digital Sky Survey (SDSS) culminates 20 years of cosmological research with the release of a comprehensive analysis of the largest 3-D map of the Universe ever created. The new results come from the extended Baryon Oscillation Spectroscopic Survey (eBOSS). The results from this effort are described in 23 papers, appearing  in today's arXiv.

ARI's researcher, Violeta Gonzalez-Perez, has been a member of eBOSS since 2016. She has co-lead the effort of producing mock catalogues of star-forming emission line galaxies (ELGs, These catalogues are pivotal to understand the systematic errors that affect the final cosmological measurements. Her work is one of the first ones of its kind with ELG galaxies, which are expected to be used widely as cosmological tracers in upcoming surveys.

In eBOSS, several tracers have been used to measure cosmological parameters in a wide range of  cosmic times. You can explore these different tracers in this video:, or interactivley here:

The SDSS-IV/eBOSS results are still compatible with the standard cosmological model, however this picture of the Universe has cracks. The SDSS-IV/eBOSS measurement of the current rate of the expansion of the Universe is about 10% lower than the value found from distances to nearby galaxies. This is really puzzling as multiple independent and very precise methods have been used to reach this conclusion.

The main cosmological results can be found in a paper ( that is summarised by Eva-Maria Müller (