Astronomers are revelling in the latest images from Euclid, a minivan-sized satellite whose panoramas of the deep cosmos are intended to shed light on the nature and evolution of the universe as a whole.
Photos released on Thursday by the European Space Agency, which launched Euclid last year, are brimming with distant galaxies while revealing foreground objects with arresting clarity. In a raft of scientific papers posted concurrently with the photos, researchers involved with the mission detail the range of ways in which their new tool can serve as an engine of cosmic discovery.
“There are going to be lots of eyes on these data,” said Will Percival, a professor of astrophysics at the University of Waterloo and one of the mission’s scientific co-ordinators. “This is modern astronomy. You don’t just look at an individual object; you build a data set and then you have thousands of scientists ready to go data mining to get the information out.”
Euclid's view of the galaxy NGC 6744 captures its central bulge, made up of older, less massive stars than those in its arms.
Judging by this week’s first release of scientific results from the mission, there is plenty of mining to be done.
As an astronomical instrument, Euclid is smaller and less powerful than NASA’s James Webb Space Telescope. However, its wide field of view – which can capture a region of sky nearly three times the area of the full moon in a single shot – is ideal for gathering information about the large-scale distribution of matter in the universe along with anything else that happens to be in the frame. The images that Euclid generates are so sharp and detailed that it would require 300 high-definition television screens arranged in a giant square just to show a single photo at its full resolution.
Among the research papers issued this week are some that make use of Euclid data to explore nearby stellar nurseries and planet formation in the Milky Way. Others delve into rich details revealed in other galaxies, both near and far.
“The quality of the first Euclid images is simply stunning,” said Allison Man, an astrophysicist at the University of British Columbia who is a member of the mission’s scientific consortium. “As a researcher on galaxy evolution, I find it fascinating that each of the detected galaxies can potentially be as complex as our own.”
Dr. Man said she hopes to use data from Euclid to illuminate how the evolution of galaxies varies depending on whether they form in dense concentrations with multiple members, or in relatively quiet cosmic suburbs where neighbours are few and far between.
But the key message to emerge this week is that Euclid is performing at the level necessary to fulfill its primary objective: shedding light on the nature of dark energy.
Discovered in 1998, dark energy is the name for a poorly understood phenomenon that is causing the expansion of the universe to accelerate. Theories for what is driving the acceleration are closely tied to the fundamental laws of nature including Einstein’s theory of general relativity. The challenge for scientists is that, whatever dark energy might be, it is far too diffuse to detect or study on Earth. As a presence, it is apparent only in the way it shapes the universe at large.
The gravity of large objects in space, like the sun, can warp space, here represented as a green grid, which distorts light passing through it.T. PYLE/CALTECH/MIT/LIGO LAB
One way that scientists can use Euclid to probe dark energy is by studying an effect known as weak gravitational lensing. It was Einstein who famously predicted that gravity can bend light, a hypothesis that was later proved to be correct by watching how the sun causes the positions of background stars to shift, as measured during a total eclipse in May, 1919.
The universe is full of matter, both seen and unseen, which similarly bends the light from more distant objects and warps their shapes, like a piece of glass with uneven thickness.
One of the images released on Thursday shows a distant cluster of galaxies, called Abell 2390. Near the cluster, the images of background galaxies are obviously stretched into long arcs by gravitational lensing.
Dr. Percival said that Euclid is especially adept at looking at objects well to the side of that central concentration where the lensing effect is imperceptible to the human eye but can still be measured statistically. This, in turn, can be used to estimate the density of matter in various directions and show how it changes over time by looking back to earlier and earlier epochs of cosmic history.
“Dark energy is causing matter to spread out more and more rapidly,” Dr. Percival said. “So we can see that the lensing diminishes as dark energy accelerates the universe.”
Ultimately, he said, the mission hopes to trace the rate of acceleration of the universe across time which will, in turn, help to guide theories that explain its nature and role in shaping cosmic history. The mission’s primary function as a tool of spatial measurement is the reason it was named after the most famous geometer of ancient history.
The Euclid spacecraft – unveiled in Cannes, France, in 2023 – can capture a wider field of view than other telescopes.VALERY HACHE/AFP via Getty Images
Since Euclid was launched on July 1, 2023, astronomers have been testing its capabilities. This week’s release represents only about 24 hours’ worth of data – a small but choice sampling of what the satellite has gathered over the past several months. During its six-year mission, the satellite is set to map approximately one-third of the sky. But results that speak directly to the dark energy question are not expected until late 2026, Dr. Percival said.
By then, Euclid will be working in parallel with the new Vera C. Rubin Observatory currently under construction in Chile. The observatory will host the largest astronomical camera ever built to continuously image the southern sky and gather data about celestial objects at every distance, including remote galaxies that can be used to trace the effects of dark energy.
“The two projects are very complementary,” said Aaron Roodman, who leads the observatory’s camera program. “A space-based telescope gives you extremely sharp images that you can’t get in a wide-field telescope from the ground. On the other hand, we will take many repeated images of every part of the sky and we’ll do it in six filter bands,” of different wavelengths.
Dr. Roodman said the current schedule will see the camera installed later this year, with the observatory set to begin scientific operations in 2025.