The Kitt Peak National Observatory is near Tucson, Arizona. Credit: AURA/P. Marenfeld.
The first seven months of the survey run by the Dark Energy Spectroscopic Instrument (DESI) have created the largest and most detailed map of the universe ever. It's only 10% of the way through its five-year mission. Physicists and astronomer will have a better understanding of the past and future of the universe once that map is completed. Scientists are learning the secrets of the most powerful sources of light in the universe thanks to the impressive technical performance and literally cosmic achievements of the survey.
The Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has primary funding for construction and operations of DESI.
The performance of the instrument, and some early astrophysics results, will be presented by scientists at a Berkeley Lab-hosted webinars this week.
One of the speakers said there was a lot of beauty to it. There are huge clusters in the distribution of the galaxies. They are the biggest structures in the universe. You can find an imprint of the very early universe within them.
This point has been reached by DESI. Construction on the instrument began in 2015. It was installed at the Kitt Peak National Observatory. The Department of Energy contracts with the National Science Foundation's NOIRLab to operate the Mayall Telescope for the DESI survey. The instrument was the first to light up. The telescope was shut down for several months after the coronaviruses outbreak, though work continued remotely. In December 2020, DESI began testing out its hardware and software, and by May 2021, it was ready to start its science survey.
The work on DESI didn't stop once the survey started. Klaus Honscheid, an instrument scientist at Ohio State University, will deliver the first paper of the CosmoPalooza DESI session. Honscheid and his team make sure the instrument runs smoothly and automatically, ideally without any input during a night's observing. The shifts are boring, which I take as a compliment, he said.
Every of the 5,000 cutting-edge robots that position optical fibers on the DESI instrument has to be controlled to ensure their positions are within 10 microns. Honscheid said that ten microns is tiny. It's not as thick as a human hair. You have to place each robot in the right place to collect the light from the billions of light-years away. I wonder how we could pull that off. The success of DESI as an instrument is something to be very proud of.
DESI has a three-dimensional scanning of the universe. The earth is in the lower left, looking out at the direction of the constellation Serpens and Hercules to a distance beyond 5 billion light years. As the video progresses, you can see the constellations Bootes and Corona Borealis. The colored points represent the 100 billion to 1 trillion stars of a galaxy. Thecosmic web is made up of dense clusters, filaments and voids. Data from DESI is used by D. Schlegel/Berkeley Lab.
Seeing the true colors of dark energy.
The primary task of the survey is to collect detailed color spectrum images of millions of galaxies across a third of the sky. By breaking down the light from each galaxy into its spectrum of colors, DESI can determine how much the light has been redshifted, which is when the universe expanded before reaching Earth. Redshifts allow DESI to see the depth of the sky.
The farther away a galaxy is, the more redshifted it is. Physicists can see clusters and superclusters of galaxies with a 3D map. When they were just ripples in the infant universe, those structures carried echoes of their initial formation. Physicists can use the data from DESI to determine the expansion history of the universe.
Guy said that the science goal was to measure the waves in the primordial plasma. It's amazing that we can detect the effects of these waves billions of years later.
The fate of the entire universe is at stake, and understanding the expansion history is crucial. Dark energy is a form of energy that is driving the expansion of the universe. As the universe expands, more dark energy pops into existence, which speeds up the expansion more, in a cycle that is driving the fraction of dark energy in the universe upwards. Will dark energy determine the fate of the universe? Will it collapse onto itself again? Will it rip itself apart? DESI is designed to learn more about how dark energy has behaved in the past by answering these questions. Einstein's theory of general relativity can be checked by comparing the expansion history with the growth history.
There are black holes and bright galaxies.
Understanding the fate of the universe will have to wait until DESI completes more of its survey. More than 10 billion years ago when the universe was still young, DESI is driving breakthrough in our understanding of the distant past.
Ragadeepika Pucha is a graduate student in astronomy at the University of Arizona. "DESI will tell us more about the physics of evolution and galaxy formation."
Pucha and her colleagues are using data to understand the behavior of black holes. Black holes are thought to be in the center of nearly every large galaxy. It's not known if small galaxies always have their own black holes at their core. Black holes can be hard to find on their own, but if they attract enough material, they become easier to spot.
The first few months of the DESI survey are depicted on the slide, as are the results of the completed SDSS survey. The furthest galaxies are 10 billion light years away. The 2-Dmap was constructed by the surveys. Each point is a universe. The DESI collaboration team is credited.
An active galactic nucleus is formed when material falling into the black hole gets hotter than the core of a star. AGNs are among the most brilliant objects in the universe. AGNs are harder to distinguish from newborn stars in smaller galaxies. More information about the cores of small galaxies will be given by the spectrum taken by DESI. Scientists will get clues about how bright AGNs formed in the very early universe.
Quasars are among the most distant objects known. "I like to think of them as lampposts, looking back in time into the history of the universe," said Victoria Fawcett, an astronomy graduate student at Durham University in the UK. The data from DESI will go back in time 11 billion years, because Quasars are excellent probes of the early universe.
The evolution of quasars are being studied by Fawcett and her colleagues. It is thought that quasars start out surrounded by dust, which reddens the light they give off, like the sun through haze. They drive off the dust as they age. It has been difficult to test this theory because of the lack of data on red quasars. The final survey data is expected to show an estimated 2.4 million quasars.
"DESI is great because it's picking up objects that are fainter and redder," said Fawcett. She says that this allows scientists to test their ideas about quasar evolution. This is not limited to quasars. Large samples of rare objects that we haven't been able to study before are among the exotic systems we're finding.
There's more to come. The survey has cataloged over 7.5 million galaxies and is adding more every month. Redshifts from 2.5 million galaxies were cataloged by DESI in November. By the end of its run, DESI is expected to have over 35 million galaxies in its catalog.
Pucha said that the data is just waiting to be analyzed. We will find a lot of amazing stuff about the universe. That's exciting for me.
The Dark Energy Spectroscopic Instrument created the largest 3D map of the universe.
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