Astrophysicists Release the Biggest Map of the Universe Yet

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only seven. after In months, a vast team of scientists working with the Dark Energy Spectroscopic Instrument has already mapped a larger part of the universe than all other 3D surveys. And since they’re only 10 percent of the way through their five-year mission, there’s more to come.

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DESI, pronounced like Desi Arnaz’s name, has revealed a spectacular cosmic web of more than 7.5 million galaxies, and will scan up to 40 million. The instrument is funded by the US Department of Energy and owned by Nicholas U. at Kitt Peak National Observatory near Tucson, Arizona. The Mayal 4-meter telescope is installed in. It measures the exact distance of galaxies from Earth and their emitted light over a range of wavelengths, obtaining quantity and quality at the same time. It will eventually cover about 8,000 square degrees, about 20 percent of the sky. The science derived from parsing the data is yet to come, but it will particularly aid astrophysicists as they investigate how the universe is expanding.

“It really is a fantastic adventure. We have been able to move forward despite the pandemic. We had to shut down for a few months and then we adapted,” says Julian Guy, DESI project scientist at Lawrence Berkeley National Laboratory, the lead body of the collaboration. Huh. Now observation and data processing are mostly automated; They say that every morning scientists get data from 100,000 galaxies collected overnight.


“It’s amazing how well this instrument is working and how well it’s designed to get to and far away from these galaxies. It’s an incredibly efficient machine for harvesting them in such a way that Two decades ago would have been mind-boggling,” says Jason Rhodes, a research scientist at the Jet Propulsion Laboratory in Pasadena who has been working on space telescopes to map galaxies. early universe.

A slice through 3-D map of galaxies from the first few months of the Sloan Digital Sky Survey (left) and the Dark Energy Spectroscopic Instrument (DESI; right). Earth is at the center, with the most distant galaxies located at a distance of 10 billion light years. Each dot represents a galaxy. This initial version of the DESI map shows only 400,000 of the 35 million galaxies that will be in the final map. Courtesy of D. Schlegel/Berkeley Lab using data from DESI
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DESI actually consists of several instruments installed within the telescope’s 14-story dome. The circular focal plane is located near the top, and is composed of 10 wedge-shaped petals, each containing 500 small robots. They are what enable the instrument’s galactic cartography: These 5,000 pencil-sized robotic motors position optical fibers that have to be precisely placed within 10 microns – less than the thickness of a human hair. This enables the instrument to collect accurate data on 5,000 galaxies at a time. The telescope then points to another region of the night sky and begins work on the next 5,000. In contrast, one of DESI’s predecessors, the Sloan Digital Sky Survey, based at a telescope in southern New Mexico, required scientists to manually drill holes in a circular aluminum plate at the telescope’s focus for each set of measurements, And they used to plug in a little fiber for every single galaxy they wanted to see.

At the bottom of the telescope are DESI’s spectrographs, which break the light from each galaxy into its full spectrum of colors like a rainbow. This allows them to measure the galaxy’s “redshift,” which tells scientists how far away it is. (Light from objects moving away from Earth appears red to us because of its longer wavelength as the universe expands.)

With the data Guy and his team already have, they can see the complex, web-like structures of galaxies they’ve been probing more than 10 billion light-years away—meaning that when the universe was They were capturing the light emitted back. Less than half of his current age. When you look up at the sky on a clear night, you can see the full extent of the Milky Way by scanning the entire sky, not just a couple of stars. Similarly, DESI uncovers these galactic megastructures only by systematically mapping a large number of galaxies over a wide area of ​​the sky.

DESI’s three-dimensional “CT scan” of the universe. Earth is at bottom left, looking in the direction of the constellations Virgo, Serpens and Hercules at a distance of more than 5 billion light-years. As this video progresses, the vantage point moves through 20 degrees toward the constellations Bootes and Corona Borealis. Each colored dot represents a galaxy, which in turn is made up of 100 billion to 1 trillion stars. Gravity groups galaxies into structures called the “cosmic web”, which consists of dense clusters, filaments, and voids.Courtesy of Schlegel/Berkeley Lab using data from DESI

“This project has a specific scientific goal: to measure the accelerating expansion of the universe very accurately,” says Guy. He refers to “dark energy,” which is simultaneously mysterious and all-encompassing, which is believed to make up about 70 percent of the universe and cause it to expand faster and faster. Guy and his colleagues hope to shed light on what dark energy really is. Their survey may also eventually solve an emerging astrophysics problem: scientists measuring the expansion rate in the nearby universe – when it was roughly its current age – and measuring the expansion rate of the universe when it was in its infancy. If yes, then there are different answers. No one knows how to explain the persistent discrepancy, but if DESI shows that dark energy evolves in some way, it could solve the problem.

Guy and his team plan their first DESI data release for 2023. This massive data dump will enable many scientists to study millions of galaxies while developing new data and machine-learning tools. “I’m curious about what one can do with artificial intelligence or deep learning with such a huge amount of data. You might find something you don’t expect. “I’m excited about it,” says cosmologist and former Sloan Digital Sky Survey researcher Shirley Ho.

In a few years, DESI won’t be the only comprehensive galactic atlas in town. Starting next year, the National Science Foundation-funded Vera Rubin Observatory, which is being built on a dry mountain in northern Chile, will catalog billions of galaxies, but with less accuracy. Astronomers are also preparing for the European Space Agency Euclid The spacecraft, with a planned 2023 launch date, and NASA’s Nancy Grace Roman Space Telescope, slated to explode in 2027. They will both carry instruments to measure the distance and spectra of the galaxies, and they will map them past what DESI can see. , parts of the deep universe that formed when it was just a couple billion years old—a child, cosmologically speaking. “Euclid and Roman are both relying on DESI to get to the nearby universe. They will build on what DESI is doing in interesting ways,” Rhodes says.

To Ho, Desi and other vast cosmic maps are a reminder of how little humanity is in the universe. “The fact that we are able to see so many galaxies is a feat. But there are a billion stars in each of those galaxies, and each of those stars may have a system like ours,” she says. “I think it’s a humbling experience to realize how insignificant we are.”

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