Posted on March 6th, 2018

Reaching Orbit – Dark Energy Spectroscopic Instrument

The Nicholas U. Mayall Telescope in Arizona is getting an upgrade that will help researchers create the most detailed 3D map of the Universe. The retrofit is for the 9-ton Dark Energy Spectroscopic Instrument (DESI).

Data from the BOSS instrument was used to create a map of the Universe. This is 1/20 of the night sky and looks back six billion years. The yellow points are celestial objects that are closer to Earth and move from red to purple as they get further away. (Credit: Daniel Eisenstein and the SDSS-III collaboration)

Its predecessor, the Baryon Oscillation Spectroscopic Survey (BOSS), is equipped with 1,000 optical fibers. By comparison, DESI is going all in with five times more fibers. The device is comprised of 5,000 fiber-optic sensors, each one the size of a pencil. The fibers are controlled by robots that position the fibers and change the survey area in space. The instrument will stare at one point in the sky, collecting light from distant objects, for 20 minutes before changing its position.

The light captured by the fibers will then be transmitted to ten powerful spectrographs for analysis. Data crunched by the spectrographs will tell researchers how fast objects are moving by analyzing their red shift. More distant objects that are moving away from Earth appear red as the visible wavelength is stretched into the red part of the spectrum. DESI will be able to look as far back as 11 billion years. These are celestial bodies whose light is so far away that it has taken 11 billion years to reach Earth. The red shift tells researchers how fast these objects are moving and therefore the speed of the expansion of the Universe and the effects of dark energy.


This is one of ten sections of the DESI instrument, each composed of 500 fiber-optic sensors. (Credit: DESI Collaboration)

Dark energy has never been directly measured, we only know that the Universe continues to expand despite the measured presence of gravity, a force that pulls objects together. We also know that the expansion of the Universe is speeding up, not slowing down. So, if gravity is bringing objects together but the net movement of the Universe as a whole is expanding outwards then there is a force at work that humans have yet to identify. Using fancy math that is over my head, scientists have calculated that roughly 68% of the Universe is comprised of dark energy.

With the help of DESI, researchers hope to unveil some of the mysteries of the Universe. The first measurements are scheduled to take place early in 2019.

Katie Nelson
Geospatial Ninja
(303) 718-7163
katie@apollomapping.com

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