The Dark Energy Spectroscopy (DESI) instrument, currently pointed at the sky from its home at the Nicholas U Mayol Telescope at Kate Peak National Observatory in Arizona, is tasked with mapping the expansion of space, investigating dark energy, and creating the most detailed three-dimensional map of the universe put together.
It’s only been seven months since the DESI mission and we already have a record-breaking 3D image of the galaxy around us, proving DESI’s capabilities and space mapping capabilities.
DESI has already cataloged and mapped more than 7.5 million galaxies, with over 1 million new galaxies being added every month. By the time the survey ends entirely in 2026, it is believed that more than 35 million galaxies will be mapped, providing astronomers with a huge library of data to prospect.
“There’s a lot of beauty in it,” says astrophysicist Julien Guy of Lawrence Berkeley National Laboratory in California.
“In the distribution of galaxies in the 3D map there are huge clusters, filaments and voids. They are the largest structures in the universe. But inside them, you find an imprint of the very early universe, and the history of its expansion since then.”
DESI consists of 5,000 optical fibers, each of which is individually controlled and positioned by its own small robot. These fibers must be positioned precisely to within 10 microns, or less than the thickness of a human hair, and then capture glimpses of light as they filter back to Earth from the universe.
Through this network of fibers, the instrument captures images of the color spectrum of millions of galaxies, covering more than a third of the entire sky, before calculating how much the light is redshifted — how much it is pushed toward the red end of the galaxy. Spectrum due to the expansion of the universe.
Since this light can take up to several billion years to reach Earth, it is possible to use redshift data to find out the depth in the universe: the higher the redshift, the further away something is. Furthermore, the structures drawn by DESI can be reversed to see the initial configuration they began with.
above: Slide through the 3D map of galaxies from the completed Sloan Digital Sky Survey (left) and the first few months of the dark energy spectroscopy instrument (right).
DESI’s main goal is to reveal more about dark energy, which is believed to make up 70% of the universe, as well as speed up its expansion. This dark energy can push galaxies into infinite expansion, causing them to collapse back into themselves or something in between — and cosmologists are keen to narrow the options.
“[DESI] It will help us search for clues about the nature of dark energy,” Carlos Frink, a cosmologist from Durham University in the UK, told the BBC.
“We will also learn more about dark matter and the role it plays in how galaxies such as the Milky Way form and how the universe evolves.”
The 3D map that has already been released shows that scientists don’t have to wait for DESI to finish its work to start benefiting from an in-depth look into space. Other DESI-improved research is exploring whether smaller galaxies have their own black holes like larger galaxies.
The best way to detect a black hole is to determine which gas, dust, and other matter is being dragged into it, but it’s not easy to see in smaller galaxies — something that the high-resolution spectra data collected by DESI should help with.
Then there is the study of quasars, especially bright galaxies backed by supermassive black holes, which serve as guideposts through billions of years of space history. DESI will be used to test a hypothesis about quasars: that they begin surrounded by an envelope of dust that gets pushed back over time.
The amount of dust around the quasar is thought to affect the color of the light it emits, making it an ideal function for DESI. The tool should be able to collect information on about 2.4 million quasars by the time the survey is completed.
“DESI is really cool because it picks up a lot of faint, red objects,” says astronomer Victoria Fawcett of Durham University.
“We’ve found a lot of exotic systems, including large samples of rare things that we haven’t been able to study in detail before.”
You can keep up with the latest news from Dark Energy Spectroscopic Instrument on its official homepage.