Dark Energy Survey releases most precise look at the universe's evolution

Observatory in Chile

The results announced today draw on data from 226 million galaxies observed over 345 nights.

  • 27 May 2021
  • 9 min read

New results from the Dark Energy Survey (DES), drawing on data from 226 million galaxies, have allowed scientists to create the largest and most precise maps of the universe’s composition and growth to date.

Scientists, including a team from the University of Portsmouth, also measured the way matter is distributed throughout the universe to see if it is consistent with predictions in the standard cosmological model, which is the best current model of the universe.

Over the course of six years, DES has surveyed 5,000 square degrees, almost one-eighth of the entire sky, in 758 nights of observation, cataloguing hundreds of millions of objects.

The results announced today draw on data from the first three years, 226 million galaxies observed over 345 nights, to create the largest and most precise maps yet of the distribution of galaxies in the universe at relatively recent epochs.

Since DES studied nearby galaxies as well as those billions of light-years away, its maps provide both a snapshot of the current large-scale structure of the universe and a movie of how that structure has evolved over the course of the past seven billion years.

Professor David Bacon, from the University’s Institute of Cosmology and Gravitation, said: “ The Universe is a strange place; mysterious constituents, which we call dark matter and dark energy, dominate its behaviour. DES continues to be one of the most exciting teams I've ever been part of, seeking to understand these weird components of the cosmos.

2.	The Dark Energy Survey photographed the night sky using the 570-megapixel Dark Energy Camera

The Dark Energy Survey photographed the night sky using the 570-megapixel Dark Energy Camera 

To test cosmologists’ current model of the universe, DES scientists compared their results with measurements from the European Space Agency’s orbiting Planck observatory.

Planck used light signals known as the cosmic microwave background to peer back to the early universe, just 400,000 years after the Big Bang. The Planck data give a precise view of the universe 13 billion years ago, and the standard cosmological model predicts how the dark matter should evolve to the present. 

If DES’s observations don’t match this prediction, there is possibly an undiscovered aspect to the universe. While there have been persistent hints from DES and several previous galaxy surveys that the current universe is a few percent less clumpy than predicted, an intriguing find worthy of further investigation, the recently released results are consistent with the Planck prediction.

DES photographed the night sky using one of the most powerful digital cameras in the world from an observatory in Chile. The Dark Energy Camera has 570 megapixels, which is nearly 50 times as powerful as an iPhone camera. 

“These analyses are truly state-of-the-art, requiring artificial intelligence and high-performance computing super-charged by the smartest young scientists around,” said Scott Dodelson, a physicist at Carnegie Mellon University who co-leads the DES Science Committee with Elisabeth Krause of the University of Arizona. “What an honour to be part of this team.” 

Ten regions of the sky were chosen as “deep fields” that the Dark Energy Camera imaged repeatedly throughout the survey. Stacking those images together allowed the scientists to glimpse more distant galaxies.

DES continues to be one of the most exciting teams I've ever been part of, seeking to understand these weird components of the cosmos.

David Bacon, Professor of Cosmology

The team then used redshift information, on the distances from earth to galaxies, from the deep fields to calibrate measurements of redshift in the rest of the survey region. This and other advancements in measurements and modelling, coupled with a threefold increase in data compared to the first year, enabled the team to pin down the density and clumpiness of the universe with unprecedented precision.  

The DES collaboration consists of over 400 scientists from 25 institutions in seven countries.

“The collaboration is remarkably young. It’s tilted strongly in the direction of postdocs and graduate students who are doing a huge amount of this work,” said DES Director and spokesperson Rich Kron, who is a Fermilab and University of Chicago scientist. “That’s really gratifying. A new generation of cosmologists are being trained using the Dark Energy Survey.”

Professor Bacon added: “This set of results is far from the end for DES; there are a further three years of data to analyse. We can hardly wait for the final conclusions about what's going on in our Universe.”

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