The Dark Energy Spectroscopic Instrument (DESI), which is currently pointing at the skies from its home in the Nicholas U. Mayall Telescope at Arizona’s Kitt Peak National Observatory, is tasked with charting the expansion of space, investigating dark energy, and creating the most detailed 3D map of the Universe ever been put together.
We’re only seven months into DESI’s mission, and we already have a record-breaking, jaw-dropping, three-dimensional picture of the galaxy all around us, demonstrating DESI’s capabilities and the potential it has for mapping space.
DESI has cataloged and charted over 7.5 million galaxies, with over a million new ones added each month. Over 35 million galaxies are expected to have been mapped by the time the scan is completed in 2026, providing astronomers with a massive library of data to mine.
“There is a lot of beauty to it,” says astrophysicist Julien Guy from the Lawrence Berkeley National Laboratory in California.
“In the distribution of the galaxies in the 3D map, there are huge clusters, filaments, and voids. They’re the biggest structures in the Universe. But within them, you find an imprint of the very early Universe, and the history of its expansion since then.”
DESI is made up of 5,000 optical fibers, each of which is individually controlled and positioned by its own tiny robot. These fibers must be precisely positioned to within 10 microns, or less than the thickness of a human hair, and then capture glimpses of light as it filters down from the cosmos to Earth.
Using this fiber network, the instrument captures color spectrum images of millions of galaxies, covering more than a third of the sky, before calculating how much the light has been redshifted – that is, how much it has been pushed towards the red end of the spectrum due to the expansion of the Universe.
Because this light can take billions of years to reach Earth, redshift data can be used to see depth in the Universe: the greater the redshift, the farther away something is. Furthermore, the structures mapped by DESI can be reverse engineered to see their original formation.
The main objective of DESI is to reveal more about the dark energy that is thought to make up 70 percent of the Universe as well as speeding up its expansion. This dark energy could drive galaxies into an infinite expansion, cause them to collapse back on themselves or something in between – and cosmologists are keen to narrow down the options.
“[DESI] will help us to search for clues about the nature of dark energy,” Carlos Frenk, a cosmologist from Durham University in the UK, told the BBC.
“We will also learn more about the dark matter and the role it plays in how galaxies like the Milky Way form and how the universe is evolving.”
The already-released 3D map demonstrates that scientists do not need to wait for DESI to complete its work to benefit from its in-depth look into space. Other DESI-enhanced research is looking into whether or not smaller galaxies have their own black holes like larger galaxies.
The best way to detect a black hole is to identify the gas, dust, and other material being dragged into it, which is difficult to do in smaller galaxies – something that DESI’s high-precision spectra data should help with.
Then there’s the study of quasars, particularly bright galaxies powered by supermassive black holes, which act as signposts back through billions of years of space history. DESI will be used to test a hypothesis around quasars: that they start off surrounded by an envelope of dust that gets driven off as time goes on.
The amount of dust around a quasar is thought to affect the color of the light it gives off, which makes it a perfect job for DESI. The instrument should be able to collect information on some 2.4 million quasars by the time its survey is completed.
“DESI is really great because it’s picking up much fainter and much redder objects,” says astronomer Victoria Fawcett from Durham University.
“We’re finding quite a lot of exotic systems, including large samples of rare objects that we just haven’t been able to study in detail before.”
You can keep up with the latest news from the Dark Energy Spectroscopic Instrument at its official home page.
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