The Dark Energy Spectroscopic Instrument (DESI), will measure light from 35 million galaxies to give new clues about dark energy.
DESI, a 3D sky-mapping project, has been approved by the US Department of Energy (DOE) and will measure the light of millions of galaxies. Construction is planned to commence next year at the Nicholas U. Mayall four metre telescope at Kitt Peak National Observatory near Tucson, Arizona, with observations beginning in January 2019.
The approval by DOE – known as Critical Decision 3 – means spending for major components of the project will start.
This expenditure will include completing manufacture of 5,000 finger-width, 10-inch-long cylindrical robots. They will point fibre-optic cables to gather light from a chosen set of galaxies, stars and massive quasars, which emit extremely large amounts of energy.
Expenses will also be used to finish the 10 fibre-fed spectrograph set, which will measure wavelengths of incoming light.
This light will provide information on the properties of the galaxies, stars and quasars and most importantly, how quickly they are moving away from us – light from distancing objects is shifted to redder wavelengths (‘redshift’).
Collecting these details can help us learn more about the nature of dark energy that drives the accelerating expansion of the universe. DESI’s observations will also provide information on the past – up to about 11 billion years ago.
DESI Director Michael Levi of Lawrence Berkeley National Laboratory's (Berkeley Lab) Physics Division said: “We're very excited that we've gotten to this step. I can't wait.”
The Spectroscopic Instrument’s robotic array will pedal through individual sets of objects several times each hour during its five-year mission. DESI will also provide a more detailed look at the patterned clustering of visible matter. This clustering occurred because of a cooling process in the early universe, producing sound wave-like oscillations through pressure and gravitational forces.
“The DESI map of galaxies will reveal patterns that result from the interplay of pressure and gravity in the first 400,000 years after the Big Bang,” said Daniel Eisenstein of Harvard University, a DESI co-spokesperson. “We’ll be using these subtle fingerprints to study the expansion history of the universe.”
The collaboration of 300 scientists and engineers from around the world includes Robert Besuner of the UC Berkeley Space Sciences Laboratory, who has stepped in as the new DESI project manager. He replaces Henry Heetderks of the Space Sciences Laboratory, who retired June 29 2016.
The latest approval from the DOE will speed up development towards completion. Six large lenses, each worth $1 million and measuring up to 1.1 metres in diameter, await treatment for an anti-reflective coating to improve transparency. The lenses will be housed in a metal frame constructed at Fermi National Accelerator Laboratory (Fermilab) to form a large stack called an optical corrector. This device will be the first piece of equipment installed at the Mayall Telescope for DESI in 2018.
DESI is one of several planned observatory projects designed to tackle cosmic mysteries such as dark energy and the universe's first light.
Risa Wechsler, of the SLAC National Accelerator Laboratory, Stanford University and DESI co-spokesperson said: “DESI will be able to make a 3D map of the universe using an order of magnitude more redshifts than currently exist.
“This will allow us to probe the physics of the universe and discover the true nature of dark energy.”