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DESI opens its 5,000 eyes to the cosmos in a bid to track dark energy

​‘First light’ for the Dark Energy Spectroscopic Instrument (DESI): as the installation phase nears completion, this new instrument is due to undergo final tests before starting to create a giant map of the sky in early 2020.

Published on 12 November 2019
For the very first time, DESI, which is installed on the Mayall Telescope (Kitt Peak, Arizona), has trained its network of 5,000 optical fibre ‘eyes’ on the night sky in a bid to see its first light. This milestone marks the start of the instrument’s final commissioning campaign before it starts scientific observations in earnest in early 2020, a mission scheduled to run for five years. 
It will record the spectrum in terms of ultraviolet, visible and infrared light from 5,000 objects at any one time. It is designed to focus automatically on a precise list of pre-selected galaxies and quasars. It will detect any light in these galaxies, breaking it down into multiple wavelengths in order to measure how far these objects are from Earth. 

Around 38 million celestial objects analysed

DESI is designed to measure the spectrum of 5,000 celestial objects every two minutes. It can scan five times as many objects twice as fast as the best existing instruments. 

Over the next five years, DESI is intended to map the position and distance of 35 million galaxies and 2.4 million quasars covering one third of the sky. With DESI scientists will have the most detailed three-dimensional maps of the universe.

Can we finally solve the mystery of dark energy?

DESI will enable scientists to investigate how the universe evolved. The distance measurements obtained for the scanned objects will be compared with predictions based on the Standard Model of Cosmology. This model assumes the existence of an unknown component, which scientists refer to as 'dark energy'. This energy is deemed to be responsible for the accelerating expansion of the universe over the past five billion years.

"DESI is a very significant advance compared to previous instruments in terms of the number of objects measured. By looking at very different objects from different eras, we can actually map the history of the universe and see what the universe is made of," explains Nathalie Palanque-Delabrouille (CEA-Irfu (Institute of Research into the Fundamental Laws of the Universe), Paris Saclay), co-spokesperson for the DESI collaboration project.

A powerful time machine

Given that the light from each star takes a certain length of time to reach us, the maps created by DESI will provide access to how the universe evolved through the ages.

The most distant galaxies and quasars that are visible with current instruments take us back 11 billion years. By multiplying the number of objects analysed by 15 compared with existing data, DESI will make it possible to create the densest map over the largest area ever recorded.

​Irfu, CEA
​Berkeley Lab
​Iniversity of California
​Aix-Marseille University
​Winlight System

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