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DESI creates the largest and most detailed map of the universe ever

The Dark Energy Spectroscopic Instrument (DESI), a multi-object survey spectrograph installed on the Nicholas U. Mayall 4-m telescope at the Kitt Peak National Observatory, has cataloged more galaxies than any other previous 3D redshift study combined, measuring 7.5 million galaxies in just seven months since the beginning of scientific operations. Yet it is only about 10% of the way through its five-year mission. When done, the phenomenally detailed 3D map will provide a better understanding of dark energy, thereby giving physicists and astronomers a better understanding of the past - and future - of the universe. Meanwhile, the study's impressive technical performance and literally cosmic results so far are helping scientists uncover the secrets behind the most powerful light sources in the universe.

A snippet of the 3D map of galaxies from the first few months of the DESI survey.  Earth is at the center, with the most distant galaxies plotted at distances of 10 billion light-years.  Each point represents a galaxy.  This version of the DESI map shows a subset of 400,000 of the 35 million galaxies that will be on the final map.  Image credit: D. Schlegel / DESI / Lawrence Berkeley National Laboratory / M. Zamani, NSF's NOIRLab.

A snippet of the 3D map of galaxies from the first few months of the DESI survey. Earth is at the center, with the most distant galaxies plotted at distances of 10 billion light-years. Each point represents a galaxy. This version of the DESI map shows a subset of 400,000 of the 35 million galaxies that will be on the final map. Image credit: D. Schlegel / DESI / Lawrence Berkeley National Laboratory / M. Zamani, NSF's NOIRLab.

The primary task of the DESI study is to collect spectra of millions of galaxies across more than a third of the entire sky.

By breaking down the light from each galaxy into its spectrum of colors, DESI can determine how much light has been redshifted - stretched toward the red end of the spectrum by expanding the universe over the billions of years it traveled before it reached Earth.

It is these redshifts that let DESI see the depths of the sky. The more redshifted a galaxy's spectrum is in general, the farther away it is.

With a 3D map of the cosmos in hand, astrophysicists can map clusters and superheaps of galaxies.

These structures carry echoes of their original formation as they were only ripples in the infant's cosmos.

"There's a lot of beauty in it," said Dr. Julien Guy, a researcher at Lawrence Berkeley National Laboratory.

"In the distribution of the galaxies on the 3D map, there are huge clusters, filaments and cavities."

"They are the largest structures in the universe. But in them you will find an imprint of the very early universe and the history of its expansion since then."

"Our scientific goal is to measure the imprint of waves in the original plasma," he added.

"It's amazing that we can actually detect the effects of these waves billions of years later, and so quickly in our study."

Understanding the history of expansion is crucial, with nothing less than the fate of the entire universe at stake.

Today, about 70% of the universe's content is dark energy, a mysterious form of energy that drives the universe's expansion ever faster.

As the universe expands, more dark energy emerges, accelerating the expansion more, in a cycle that drives the fraction of dark energy in the universe ever upward.

Dark energy will ultimately determine the fate of the universe: will it expand forever? Will it collapse into itself again, in a Big Bang the other way around? Or will it tear itself apart?

Answering these questions means learning more about how dark energy has behaved in the past - and that's exactly what DESI is designed to do.

And by comparing the history of expansion with the history of growth, cosmologists can check whether Einstein's general theory of relativity holds over these enormous spans of space and time.

But understanding the fate of the universe will have to wait until DESI has completed more of its study.

Meanwhile, DESI is already making a breakthrough in our understanding of the distant past, more than 10 billion years ago, when galaxies were still young.

"It's pretty amazing," said DESI project manager Ragadeepika Pucha, a graduate student at the University of Arizona.

"DESI will tell us more about the physics behind galaxy formation and evolution."

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