5,000 “eyes” will track the expansion of the Universe

DESI’s focal plate with its 5,000 robot “eyes” (credit: National Optical Astronomy Observatory)

DESI’s focal plate with its 5,000 robot “eyes” (credit: National Optical Astronomy Observatory)

The Dark Energy Spectroscopic Instrument (DESI), is a US-led project that will measure the accelerated expansion of the Universe in order to reveal the nature of dark energy. The DESI project, which has received significant contributions from EPFL’s astrophysicists, is entering its final testing phase, gearing up to charter the skies.

The Dark Energy Spectroscopic Instrument (DESI) was developed to probe the nature of dark energy through the detailed measurement of the accelerated expansion of the universe. Dark Energy is a mysterious component that makes up about 68% of the mass-energy budget of today’s Universe. DESI has now announced its “First Light”, entering its final testing and commissioning phase on the telescope, meaning that the instrument will be ready to begin science observations in early 2020. The first major release of data is expected in 2021.

Installed on the Mayall telescope at Kitt Peak National Observatory, DESI will spend the next four years obtaining optical spectra from tens of millions of galaxies and quasars, constructing a 3D map spanning the nearby universe up to 11 billion light-years.

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. The latter has been conducted as part of the interdisciplinary "Astrobots" group, which includes EPFL’s Laboratory of Astrophysics (LASTRO), as well as Mohamed Bouri and Denis Gillett’s teams from the School of Engineering, all of whom will be involved in processing the enormous amount of data that will be coming in from DESI.

The Astrobots group also procured most of the parts used for the construction of the fiber-positioner robots, which were manufactured the companies Maxon Motor in Switzerland and Namiki in Japan. In addition, the group contributed to the development of the firmware of the DESI positioner, and also carried out some tilt-verification tests on a few DESI positioners to validate their performance. An EPFL engineer also spent several months in the US to assist and help with the production of the positioners.

EPFL and the Swiss National Science Foundation have contributed almost 1 million CHF to the DESI project.