3-D Galaxy-mapping project entersconstruction phase9 August 2016

The first "petal" machined for the Dark EnergySpectroscopic Instrument (DESI) is shown in thesephotos. Ten of these petals, which together will hold5,000 robots (like the one in the lower right photo) --each pointing a thin fiber-optic cable at separate skyobjects -- will be installed in DESI. Credit: JoeSilber/Berkeley Lab

A 3-D sky-mapping project that will measure thelight of millions of galaxies has receivedformal—approval from the U.S. Department ofEnergy to move forward with construction.Installation of the project, called DESI (DarkEnergy Spectroscopic Instrument), is set to beginnext year at the Nicholas U. Mayall 4-metertelescope at Kitt Peak National Observatory nearTucson, Ariz., with observations starting up inJanuary 2019.

This latest DOE approval step, known as CriticalDecision 3, triggers spending for majorcomponents of the project, including the remainderof the 5,000 finger-width, 10-inch-long cylindricalrobots that will precisely point the fiber-optic cablesto gather the light from a chosen set of galaxies,stars, and brilliant objects called quasars. Thespending will also be used to complete the set of10 fiber-fed spectrographs that will precisely

measure different wavelengths of incoming light.

This light will tell us about the properties of thegalaxies, stars, and quasars, and most importantly,how quickly they are moving away from us—lightfrom objects that are moving away from us isshifted to redder wavelengths ("redshift"). Thesedetails can help us learn more about the nature ofdark energy that is driving the acceleratingexpansion of the universe. DESI's observations willprovide a deep look back in time, up to about 11billion years ago.

"We're very excited—ecstatic—that we've gotten tothis step," said DESI Director Michael Levi ofLawrence Berkeley National Laboratory's (BerkeleyLab) Physics Division.

"This brings DESI closer to its five-year mission togo where no map has gone before in the universe,"added David Schlegel of Berkeley Lab, a co-projectscientist for DESI. "I can't wait."

DESI's robotic array will cycle through separatesets of objects several times each hour during itsfive-year mission. It will look at one-third of the skyand will capture more than 10 times as much dataas a predecessor called BOSS, the BaryonOscillation Spectroscopic Survey.

1 / 4

The Dark Energy Spectroscopic Instrument (DESI),shown in this illustration, will be mounted on the 4-meterMayall telescope at Kitt Peak National Observatory nearTucson, Ariz. It will collect data on light from 35 milliongalaxies and quasars to make the biggest 3-D map of theuniverse ever. Credit: R. Lafever, J. Moustakas/DESICollaboration

DESI will provide a more detailed look at thepatterned clustering of visible matter in the nightsky across a larger range of distances. Thisclustering was set in motion by a cooling process inthe early universe that produced sound wave-likeoscillations through a combination of pressure andgravitational forces. DESI will also provide a moreprecise measure of how the universe has spreadout over time, and help us understand galaxyevolution and dark matter, which is invisible butinferred from its gravitational effects on normalmatter.

"The DESI map of galaxies will reveal patterns thatresult from the interplay of pressure and gravity inthe first 400,000 years after the Big Bang," saidDaniel Eisenstein of Harvard University, a DESI co-spokesperson. "We'll be using these subtlefingerprints to study the expansion history of theuniverse."

The DESI collaboration has grown to include about300 scientists and engineers from about 45institutions around the globe. The leadership teamincludes Robert Besuner of the UC Berkeley SpaceSciences Laboratory, who has stepped in as thenew DESI project manager. He replaces HenryHeetderks of the Space Sciences Laboratory, whoretired June 29.

The project's multiple sources of financial supportand its use of an existing telescope have helped tokeep DESI on a fast track, Levi said. "Now the hardwork accelerates," he added.

With the latest approval, a pipeline of developmentefforts will move quickly toward completion. Sixlarge lenses, each worth $1 million and measuringup to 1.1 meters in diameter, await treatment withan antireflective coating to improve theirtransparency.

The lenses will be housed in a metal frame beingconstructed at Fermi National AcceleratorLaboratory (Fermilab) to form a minivan-sized stackknown as an optical corrector. This device will bethe first piece of equipment installed at the MayallTelescope for DESI in 2018.

This is a view of the ProtoDESI setup during assembly atBerkeley Lab, with the underside of the robotic fiber-positioners visible at left. ProtoDESI is now installed atthe 4-meter Mayall Telescope at Kitt Peak NationalObservatory near Tucson, Ariz. Credit: PaulMueller/Berkeley Lab

2 / 4

To prepare for DESI data analysis, softwareengineers are using supercomputers at BerkeleyLab's National Energy Research ScientificComputing Center (NERSC) to simulate the datagathered by DESI. NERSC is a DOE Office ofScience User Facility.

Also, three sky surveys are now collecting imagesof the faint galaxies that DESI will target. Data fromthese surveys is periodically released on a publicsite at http://legacysurvey.org, and observationaldata gathered by DESI will also be publiclyreleased.

"I like to think of the imaging surveys as building the2-D maps, while DESI adds the third dimension,"said Dustin Lang, a DESI imaging scientist with theUniversity of Toronto. "The crucial third dimensionallows us to measure how galaxies cluster togetherin space over the history of the universe."

A prototype instrument called ProtoDESI has beeninstalled at the Mayall Telescope for a two-monthrun. ProtoDESI will use four small robots to test outthe fiber-positioning system and includes camerasand other components to prepare for the full DESIproject.

"This is a great time to be an astroparticle physicist.DOE's program of building new instruments likeDESI will provide the data that will let us take thenext step in understanding the formation of ouruniverse," said Fermilab's Brenna Flaugher, co-project scientist for DESI and project manager ofDECam, the camera for the Dark Energy Survey,an ambitious imaging survey currently underway.

DESI is one of several planned next-generationobservatory projects designed to confront cosmicmysteries including dark energy, dark matter, andthe universe's first light, known as the cosmicmicrowave background.

"DESI will be able to make a 3D map of theuniverse using an order of magnitude moreredshifts than currently exist," said Risa Wechslerof the SLAC National Accelerator Laboratory,Stanford University and DESI co-spokesperson."This will allow us to probe the physics of theuniverse and discover the true nature of dark

energy."

Provided by Lawrence Berkeley NationalLaboratory

3 / 4

APA citation: 3-D Galaxy-mapping project enters construction phase (2016, August 9) retrieved 15 April2022 from https://phys.org/news/2016-08-d-galaxy-mapping-phase.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, nopart may be reproduced without the written permission. The content is provided for information purposes only.

Powered by TCPDF (www.tcpdf.org)

4 / 4