On top of Kitt Peak in the Arizona Desert, a robotic surveyor just completed a five year mission to catalogue the positions of tens of millions of galaxies. The Dark Energy Spectroscopic Instrument (DESI) has now created the largest, most detailed 3D map of our universe ever constructed. And it\u2019s not done yet, its main mission has been extended through 2028.<\/p>\n
DESI itself uses around 5,000 robotic \u201ceyes\u201d – essentially fiber-optic positioners used to capture photons that had been traveling for billions of years to finally hit Earth. Originally it was planned to map over 34 million galaxies over its five year main mission. By the time the survey was completed on April 14th, it had captured data for a staggering 47 million galaxies and quasars, in addition to 20 million regular stars in the Milky Way. <\/p>\n
The project team was rightfully proud of this achievement. \u201cThe five-year DESI project has been a spectacular success,\u201d said Michael Levi, DESI director and a scientist at Lawrence Berkeley National Laboratory, in a press release. \u201cThe instrument performed better than anticipated\u2026the size and scope of the map and how quickly we\u2019ve been able to execute is phenomenal.\u201d<\/p>\n
Fraser discusses how dark energy affects the expansion of the universe.<\/p>\n
Much of the science for this data set is still in the works, but there is one big question that most scientists are hopeful to answer – is dark energy evolving? Dark energy, which is the mysterious force that makes up roughly 70% of the universe, is also responsible for its accelerating expansion. In other words, it\u2019s what will ultimately decide the fate of the universe. Scientists have long treated it as a \u201ccosmological constant\u201d – something unchanging over time. But early results from the first three years of DESI\u2019s survey \u201chint\u201d that dark energy might actually be changing as the universe ages.<\/p>\n
If the five year dataset confirms this theory, it would represent a fundamental paradigm shift in cosmology. It would also require scientists to rethink whether the universe will end in a Big Rip, Big Freeze, or Big Bounce, or something else entirely new. Gregory Tarl\u00e9, a founding member of DESI and professor at the University of Michigan, put it well: \u201cThe stunning discovery by DESI that dark energy is likely dynamic has forced us to rethink everything we thought we understood.\u201d<\/p>\n
While scientists are chewing over the full five year data set, DESI will be back to collecting data for a few more years. The Department of Energy, which funded the project, has decided to extend the mission through 2028. During the \u201cDESI-II\u201d phase of the instrument, the survey will expand its coverage by another 20% of the sky, bringing the total mapped area up from 14,000 square degrees to 16,800 square degrees. For reference, a full moon is 0.2 square degrees, and the entire sky is around 41,000 square degrees.<\/p>\n
Fraser interviews one of DESI\u2019s scientists, Dr. John Moustakas <\/p>\n
To do so, it will focus on more difficult areas to survey. These include the area close to the plane of the Milky Way, where bright nearby stars can make it more difficult to see faint distant objects. Additional observations will look further south, where the telescope will have to contend with additional interference from Earth\u2019s atmosphere. It will also revisit the existing mapped area to capture more information on distant and faint \u201cluminous red galaxies\u201d that weren\u2019t necessarily captured in the first survey.<\/p>\n
Don\u2019t expect any of this to happen quickly, though. The full data release for the five-year survey likely won\u2019t happen until 2027. And the statistical analysis to find whether dark energy is changing or not will take much longer than that. For now, let\u2019s just appreciate the fact that we have an instrument that has successfully scanned 47 million objects in the universe. That in itself is an amazing feat worth celebrating.<\/p>\n
Learn More:<\/p>\n
LBNL – DESI Completes Planned 3D Map of the Universe and Continues Exploring<\/a><\/p>\n UT – A Cosmic Survey Reveals the Universe’s Hidden Side<\/a><\/p>\n