A snippet of a 3D galaxy map from the first few months of the DESI survey. Earth is located at the center, where the farthest galaxies are plotted at a distance of 10 billion light years. Each dot represents a galaxy. This version of the DESI map shows parts of the 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, NOIRLab NSF.
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The main mission of the DESI survey is to collect the spectra of millions of galaxies in more than a third of the entire sky.
By dividing the light from each galaxy into their color spectrum, DESI can measure the redshift of light — stretching towards the red end of the spectrum as the universe expands over the billions of years it has passed before reaching Earth.
This red shift is what makes DESI see the depths of the sky. The larger the redshift of the galaxy’s spectrum in general, the farther away it is.
With a 3-D map of the universe in hand, astrophysicists can plot galaxy clusters and superclusters.
The structures echo their initial formation, when they were just ripples in the infant universe.
“There’s a lot of beauty in this,” said Dr. Julian Gay, researcher at Lawrence Berkeley National Laboratory.
“In the distribution of galaxies on the 3D map, there are large clusters, filaments, and voids.”
“They are the largest structures in the universe. But in it, you find traces of the earliest universe, and the history of its expansion since then.”
“Our scientific goal is to measure wave signatures in ancient plasmas,” he added.
“It’s amazing that we were actually able to detect this wave effect after billions of years, and so quickly in our survey.”
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Understanding the history of expansion is very important, because nothing less than the fate of the entire universe is at stake.
Currently, about 70% of the content of the universe is dark energy, a mysterious form of energy that is driving the universe’s expansion faster.
As the universe expands, more dark energy emerges, accelerating further expansion, in a cycle that pushes some of the universe’s dark energy continuously upwards.
Dark energy will ultimately determine the fate of the universe: will it expand forever? Will it collapse on its own again, with a big upside down bang? Or will he tear himself apart?
Answering these questions means learning more about how dark energy behaved in the past – and that’s what DESI was designed for.
And by comparing the history of expansion with the history of growth, cosmologists can verify whether Einstein’s general theory of relativity can hold up over this vast expanse of space and time.
But understanding the fate of the universe will have to wait until DESI completes more of its surveys.
Meanwhile, DESI has driven breakthroughs in our understanding of the distant past, more than 10 billion years ago when galaxies were young.
“It’s absolutely amazing,” said DESI Project Director Ragadeepika Pucha, a graduate student at the University of Arizona.
“DESI will tell us more about the physics of galaxy formation and evolution.”
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