By Will Dunham
Nov 12 (Reuters) - The European Space Agency has released its first big collection of data from the orbiting Euclid telescope's mission to map the universe's large-scale structure, including observations of more than 900 million galaxies, as scientists investigate the puzzling cosmic components dark matter and dark energy.
The data unveiled on Thursday covered a survey of the sky equal to about 9,500 times the size of the moon as viewed from Earth. The mission's goal is to complete the largest-ever
three-dimensional atlas of the cosmos, spanning more than a third of the sky, in 2031.
Thursday's release encompassed around 13 months of Euclid observations, totaling an enormous 1.7 petabytes — 1.7 million gigabytes — of data.
"It marks a major milestone for ESA's Euclid mission and for everyone involved," said astrophysicist Valeria Pettorino, ESA's Euclid project scientist.
Euclid, launched from Florida in 2023, is gathering data on how the universe has expanded and how its structure has formed over time while amassing information about the nature of dark energy and dark matter and the role of gravity on large scales.
"Euclid will not just take images of galaxies in the sky, in two dimensions, but will also measure their distance, the third dimension. This will tell us where galaxies are in space and time, across 10 billion years, and in all directions beyond our galactic plane," Pettorino said.
"Galaxies cluster along filaments, surrounded by empty space, and form a network that we call the cosmic web. Euclid will reconstruct the cosmic web and how it has grown over time. This is important because the exact configuration of the cosmic web, how many clusters or voids are there, how fast it changed, depend on the properties of dark energy and dark matter," Pettorino said.
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 about 5% of the contents. Dark matter, known from the gravitational effects it exerts on galactic scales, is invisible material that may make up about 27% of the cosmos. Dark energy, thought to be responsible for the accelerated expansion of the universe, may account for 68%.
Dark matter and dark energy do not emit or absorb light and cannot be directly observed.
Previous Euclid data releases covered only a few days of observations. The newly released dataset includes more than a year of data and still spans only 14% of the total sky area Euclid is due to survey in visible and near-infrared light over six years. This data release will be completed next year with the first results on dark energy and dark matter.
GRAVITATIONAL LENSING
Light traveling toward Earth from faraway galaxies can be bent and distorted by normal matter and dark matter in the foreground, an effect called gravitational lensing. Thus, the nearer galaxy's gravity warps the light coming from the one behind.
Gravitational lensing is one of the tools being used to study dark matter's distribution. The new Euclid data includes about 15,000 strong gravitational lens candidates, exceeding the total number discovered in the previous half century.
"Gravitational lenses are nature's own weighing scales," said Natalie Lines, a doctoral student in astrophysics at the University of Portsmouth in England and a member of the Euclid Consortium of scientists.
"How strongly the light is bent tells us how much matter a galaxy contains, including invisible components like dark matter. With thousands of lenses, we can study how dark matter is spread through galaxies and understand how galaxies form and evolve over cosmic time," Lines said.
Lines noted the sharpness of the Euclid images over a huge area of the cosmos.
"Telescopes on Earth can cover large areas of the night sky, but their view is blurred by the atmosphere. The Hubble and James Webb space telescopes take beautifully sharp images, but only of tiny patches of sky. Euclid does both at once, and that is crucial for finding things that are small and rare, like strong gravitational lenses," Lines said.
Looking across vast distances means peering into the past because of the time needed for light from distant objects to reach us. The most distant objects Euclid has viewed are quasars, the brilliant cores of galaxies powered by supermassive black holes. The telescope has pinpointed 60 million of them.
"Euclid has found some dating back to when the universe was just 5% of its current age, so their light set off around 13 billion years ago," Lines said.
(Reporting by Will Dunham in Washington; Editing by Daniel Wallis)
