Saturday, September 24, 2022

DESI creates the largest and most detailed map of the universe ever

It’s just getting started.

The Dark Energy Spectroscopic Instrument (DESI), an international science collaboration managed by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), has smashed through; previous records for 3D galaxy surveys. It has created the largest and most detailed map of the universe ever.

DESI has cataloged more galaxies than all other previous 3D redshift surveys combined. Since it started science operations, the DESI has measured 7.5 million galaxies in only seven months. Yet it’s only about 10% of the way through its five-year mission.

Once it’s done surveying, the phenomenally detailed 3D map will yield a better understanding of dark energy and thereby give physicists and astronomers a better experience of the past – and future – of the universe.

Berkeley Lab scientist Julien Guy, one of the speakers, said, “There is a lot of beauty to it. There are huge clusters, filaments, and voids in the distribution of the galaxies in the 3D map. 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.”

Physicist Klaus Honscheid of Ohio State University said, “But work on DESI itself didn’t end once the survey started. It’s constant work that goes on to make this instrument perform.”

The primary task of the survey includes collecting detailed color spectrum images of millions of galaxies. Later, the DESI breaks down the light from each galaxy into its spectrum to ascertain how much light is stretched out toward the red end of the spectrum by the expansion of the universe. These redshifts allow DESI to determine the depth of the cosmos.

The 3D map of the cosmos can help physicists to chart clusters and superclusters of galaxies. Those structures carry echoes of their initial formation. Extraction of those echoes helps physicists determine the expansion history of the universe.

Guy said, “Our science goal is to measure the imprint of waves in the primordial plasma. t’s astounding that we can detect the effect of these waves billions of years later and so soon in our survey.”

DESI’s main goal is to answer fundamental questions of the universe: will it expand forever? Will it collapse onto itself again, in a Big Bang in reverse? Or will it rip itself apart? 

Answering these questions means learning more about how dark energy has behaved in the past. But, it would take a long run; hence physicists need to keep patience until DESI has completed more of its survey. In the meantime, DESI is already driving breakthroughs in our understanding of the distant past, more than 10 billion years ago when galaxies were still young.

Ragadeepika Pucha, a graduate student in astronomy at the University of Arizona working on DESI, said, “It’s pretty amazing. DESI will tell us more about the physics of galaxy formation and evolution.”

Using DESI data, physicists are trying to understand the behavior of intermediate-mass black holes in small galaxies. It remains elusive whether small galaxies contain black holes at their cores.

It isn’t easy to spot black holes, but they become easier to spot if they attract enough material. The material falling into the black hole heats up and creates an active galactic nucleus (AGN).

AGNs in large galaxies are among the brightest objects in the known universe. But, in smaller galaxies, AGNs are much fainter and harder to distinguish from newborn stars.

The spectra taken by DESI can yield more information about the cores of small galaxies than ever before.

In addition, understanding the evolution of quasars could be excellent probes of the early universe because of their sheer power. The team is using DESI data to understand the evolution of quasars themselves.

Quasars are believed to be originated from an envelope of dust, which reddens the light they give off, like the sun through the haze. As they age, they drive off this dust and become bluer. But it has been hard to test this theory because of the paucity of data on red quasars.

DESI’s three-dimensional “CT scan” of the Universe. The earth is in the lower left, looking out over 5 billion light-years in the direction of the constellation Virgo. As the video progresses, the perspective sweeps toward the constellation Bootes. Each colored point represents a galaxy, which in turn is composed of hundreds of billions of stars. Gravity has pulled the galaxies into a “cosmic web” of dense clusters, filaments and voids. (Credit: D. Schlegel/Berkeley Lab using data from DESI)

Fawcett said“DESI is changing that, finding more quasars than any prior survey, with an estimated 2.4 million quasars expected in the final survey data.”

“DESI is great because it’s picking up much fainter and much redder objects. That allows scientists to test ideas about quasar evolution that just couldn’t be tested before. And this isn’t just limited to quasars. 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.”

There’s more to come for DESI.

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