Dark Energy Spectroscopic Instrument (DESI)

The Dark Energy Spectroscopic Instrument (DESI) will measure the effect of dark energy on the expansion of the universe. It will obtain optical spectra for tens of millions of galaxies and quasars, constructing a 3D map spanning the nearby universe to 11 billion light years. The DESI Survey will be conducted on the Mayall 4-meter telescope at Kitt Peak National Observatory in the United States.

To do this, DESI will use 5,000 fiber-optic “eyes” to capture light from 5,000 different objects – mostly galaxies, but also quasars and some stars, although the latter will be mostly for calibration purposes. DESI is designed to automatically point at preselected sets of galaxies, gather their light, and then using ten spectrographs split that light into narrow bands of color to precisely map the distance of those galaxies from Earth.

Through the detailed analysis of the 3D distribution of galaxies and quasars, the scientists will be able to derive how much the universe has expanded as the function of the galaxies’ light traveled to Earth. Ideally, DESI can cycle through a set of about 5,000 galaxies every 20 minutes, thus measuring the distance of nearly one million of galaxies every 30 nights of observation.

EPFL scientists have contributed to the development of the survey’s targeting strategy (deciding which of the galaxies will be observed), as well as through the development of the robotic fiber-positioner system. 

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