After five years of scanning the sky, the Dark Energy Spectroscopic Instrument (DESI) has completed the largest high-resolution 3D map of our universe to date. DESI, which began its main scientific survey in May 2021, has amassed data on more than 47 million galaxies and quasars, eclipsing its original goal of mapping 34 million galaxies.
The scientists involved in this project will closely scrutinize the data collected by DESI thus far, tracking down clues on dark energy, a mysterious force that is causing the universe to expand at an accelerating rate. Given the success of its main survey, DESI will now continue mapping the sky through 2028 to expand its search for dark energy.
“DESI’s five-year survey has been spectacularly successful,” said Michael Levi, DESI director and a scientist at Berkeley Lab, in a statement. “The instrument performed better than anticipated. The results have been incredibly exciting. And the size and scope of the map and how quickly we’ve been able to execute is phenomenal. We’re going to celebrate completion of the original survey and then get started on the work of churning through the data, because we’re all curious about what new surprises are waiting for us.”
DESI’s Dark Energy Mission
As the world’s most powerful multi-object survey spectrograph, DESI operates from the U.S. National Science Foundation’s Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory in Arizona, which is overseen by the NSF NOIRlab.
Throughout its five-year survey, DESI has traced dark energy’s influence on the universe by capturing light from galaxies and quasars (the very bright cores of galaxies powered by supermassive black holes) across a span of 11 billion years.
One of the most significant takeaways of DESI’s survey is that scientists may have to rethink how dark energy — which makes up around 70 percent of the universe — behaves. According to the Berkeley Lab, the standard model of cosmology doesn’t fully align with recent DESI observations; dark energy, previously believed to be a “cosmological constant,” might actually be evolving based on data from the survey’s first three years.
Having mapped more than 47 million galaxies and quasars (along with more than 20 million nearby stars), DESI has measured cosmological data for six times as many galaxies and quasars as all previous measurements combined. The scientific collaboration behind DESI — involving more than 900 researchers from more than 70 institutions — will now begin processing the survey data, with the first dark energy results expected to arrive in 2027.
Read More: The Universe Started as a “Hot Soup of Particles and Photons” 13.8 Billion Years Ago
Splitting Light From Galaxies
DESI is capable of cycling through a new set of 5,000 galaxies every 20 minutes, amounting to more than 100,000 galaxies a night, according to NOIRlab. It does so with the help of robotic positioners that automatically point DESI’s 5,000 fiber-optic eyes at preselected sets of galaxies; 10 spectrographs then split light from the galaxies into separate colors to determine their position, velocity, and physical properties.
“We’ve learned about the instrument over five years, and we know its personality and behavior pretty well. That’s important because having the instrument be so efficient is why we’re here at the end of DESI’s original survey with such great data and so much science coming out,” said Connie Rockosi, co-instrument scientist for DESI and a professor at UC Santa Cruz and UC Observatories, in the release.
An Expanding Map of the Night Sky
With DESI’s operations extended through 2028, it will grow its map by about 20 percent from 14,000 square degrees to 17,000 square degrees (the full sky has over 41,000 square degrees). This will give DESI a chance to take a closer look at areas that aren’t as clear, such as those obscured by bright stars, and revisit previously scanned areas to gather more data from a set of galaxies called “luminous red galaxies.”
“We’ve built a remarkable piece of equipment that met all our expectations and then some,” Levi said. “Now we’re pushing beyond our original plan. We don’t know what we’ll find, but we think it’ll be pretty exciting.”
Read More: Waiting for selection…
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