Euclid mission data release is step toward grand atlas of the cosmos

By Will Dunham

(Reuters) - The European Space Agency has released its first tranche of data from the Euclid space telescope's mission to map the universe's large-scale structure in order to better understand the mysterious cosmic components dark energy and dark matter.

Scientists unveiled on Wednesday Euclid's observations of three patches of the sky populated by a panoply of galaxies. The data covered a survey of the sky equal to more than 300 times the size of the moon as viewed from Earth - a step toward the Euclid mission's goal of fashioning a grand atlas of the cosmos in exquisite detail, spanning more than a third of the sky.

Euclid, launched from Florida in 2023 on a planned six-year mission, is an orbiting observatory gathering data on how the universe has expanded and how its structure has formed over time and amassing information about the nature of dark energy and dark matter and the role of gravity on large scales.

The survey areas disclosed on Wednesday account for only about half a percent of the mission's eventual goal. The data represents just one week of observations including one scan of each of the three regions, but it covers 26 million galaxies up to 10.5 billion light-years away. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

The Big Bang event roughly 13.8 billion years ago initiated the universe, which has been expanding ever since.

The universe's contents include ordinary matter as well as dark matter and dark energy. Ordinary matter - stars, planets, gas, dust and all the familiar stuff on Earth - represents perhaps 5% of the contents. Dark matter is invisible material that may make up about 27% of the cosmos. Dark energy, an enigmatic component thought to be responsible for the accelerated expansion of the universe, may account for 68%.

The newly released Euclid images hint at the large-scale organization of galaxies in what is known as the cosmic web, essentially the backbone of the universe. In this web, there are concentrations of galaxies with voids of space in between, as if the galaxies were sitting on vast empty bubbles.

The cosmic web's structure offers clues about dark matter and dark energy, according to the researchers.

Astrophysicist Carole Mundell, the European Space Agency's director of science, called Euclid a "dark detective."

"We now understand about 5% of the universe," Mundell said. "The other 95% is dark and is unknown."

Euclid measures the various shapes and the distribution of galaxies with its high-resolution imaging visible instrument, or VIS, while its near-infrared instrument, or NISP, determines galaxy distances and masses. Euclid eventually is expected to obtain images of more than 1.5 billion galaxies.

"It is exploring more distant objects in the universe with a greater amount of sky explored than any survey before for objects so far away," astrophysicist Chris Duffy of Lancaster University in England, one of the scientists involved in the research, said of Euclid.

Duffy's part of the Euclid research focuses upon transient objects - ones that appear only briefly - such as stellar explosions called supernovae seen in the observations.

A first detailed catalog of more than 380,000 galaxies of various shapes and sizes, classified according to features such as spiral arms and central bars as well as traits that indicate a galactic merger, was released on Wednesday.

This represents "the first chunk of what will be the largest-ever catalog of the detailed appearance of galaxies," said University of Toronto astrophysicist Mike Walmsley, one of the Euclid scientists.

Light traveling toward Earth from faraway galaxies is bent and distorted by normal matter and dark matter in the foreground in an effect called gravitational lensing. It is one of the tools used by Euclid to study how dark matter is distributed. Researchers have been sifting through the Euclid data to identify strong gravitational lenses, and have identified about 500 such candidates.

"The invisible dark matter in massive galaxies warps space, bending light rays like a magnifying glass. This magnifies and distorts the galaxies behind them into arcs and rings, and measuring the distortion lets us measure the invisible dark matter. But the galaxies must be very precisely aligned, so this strong lensing effect is very rare," Walmsley said.

"Euclid is the best instrument ever built for finding these, because it can take an exceptionally sharp image of wide patches of sky – while telescopes like Hubble and the James Webb Space Telescope are designed to look at much smaller patches," Walmsley added.

The next Euclid data release, planned for October 2026, will cover an area 30 times larger than Wednesday's release.

(Reporting by Will Dunham in Washington, Editing by Rosalba O'Brien)