Scientists leading the European Space Agency’s Euclid space telescope mission have just released its breathtaking first science images, taken only four months after launch. These new space photos reveal spectacular snapshots of the vast structure of the cosmos, including a massive galaxy cluster in the Perseus constellation, an object nicknamed the “Hidden Galaxy,” an irregularly structured galaxy, a globular cluster packed with myriad stars, and the gorgeous Horsehead Nebula.
Euclid mission leaders announced the first images today at an event at ESA Space Operations Centre in Darmstadt, Germany. Carole Mundell, head of ESA’s science program, introduced the images. “Today is an iconic day. We’ve reached all of the engineering milestones of our mission and we’re finally able to enter into our science mission,” she said.
Mundell and her colleagues emphasized the space telescope’s potential for studying the large-scale structure of the universe. “I’m looking forward to the insights Euclid will give us, especially to understand what dark matter and dark energy really are,” said Josef Aschbacher, ESA Director General.
“It’s a big achievement. The first images are wonderful. They are up to expectations in terms of quality and precision, so we are very hopeful for the rest of the mission,” said Francis Bernardeau, the Euclid Consortium deputy lead and an astrophysicist at CEA Paris-Saclay, speaking to WIRED the day before the event.
These images are just the beginning of Euclid’s mission: By the end of this decade, the telescope will survey billions of galaxies like these, parsing over 15,000 square degrees—about one third of the sky—and looking back through 10 billion years of cosmic time. Together, these images will create unprecedented three-dimensional views spanning most of the life of the universe.
This new generation of space photos will also demonstrate the sensitivity of Euclid’s two instruments, which simultaneously photograph objects at optical and near-infrared wavelengths. They also measure objects’ spectra, or graphs showing the intensity of light emitted at a range of wavelengths. These measurements indicate an object’s distance and chemical composition, among other things.
The details in the Perseus cluster image (shown above) demonstrate Euclid’s power and potential. The cluster’s gravity—and that of invisible dark matter particles—binds about 200 galaxies together. It’s also part of a larger network, a supercluster of around 1,000 galaxies swirling around its outskirts, sort of an extended galactic family. Tens of thousands of additional galaxies lurk in the background of the image, showing how Euclid can survey many objects at once.
Euclid can capture details of individual objects, like the spiral galaxy IC 342 (shown above), also known as Caldwell 5 or the “Hidden Galaxy,” because it’s difficult to see with optical telescopes. The fact that this galaxy’s stars and dust are so clear to Euclid shows the benefits of an infrared view: It allows the faint galaxy to be seen even though it’s hiding behind the equator of the Milky Way, whose dust blocks visible light.
While that galaxy and our own display fancy spiral arms, most galaxies are actually much smaller and irregularly structured, including the one in the image above, known as NGC 6822. Over billions of years, dwarf galaxies like this densely packed one can become the building blocks of larger galaxies.
Globular clusters like the one in the image above, called NGC 6397, are typically groups of hundreds of thousands of stars bound by gravity. But unlike galaxies, they lack dark matter. This is the second-closest globular cluster to Earth, about 7,800 light-years away.
Everyone loves the Horsehead Nebula, also known as Barnard 33, which is part of the constellation Orion. (NASA’s James Webb Space Telescope and Hubble have been used to image the exquisite stellar nursery as well.) Two images from Euclid are shown below.
As Euclid’s science mission gets underway, more images like these will aid astrophysicists’ efforts to better understand how galaxies form and evolve, to study how fast the universe is expanding, and to investigate the mysterious nature of dark matter and dark energy, which can only be probed indirectly through their gravitational and cosmological effects on celestial bodies. Euclid’s wide field of view sets it apart from the JWST, whose strengths lie in capturing deeper and more focused images of individual objects rather than of huge swaths of the sky.
Euclid will also enable astrophysicists to develop larger and higher-resolution maps of dark matter structures than the ESA’s Planck space telescope. Astrophysicists will study dark matter with Euclid’s galaxy catalogs using statistical tools and a phenomenon known as weak gravitational lensing. That involves investigating how massive clumps of foreground dark matter deflect the light we see from background galaxies—slightly, but predictably, distorting their shapes.
Michael Seiffert, a Jet Propulsion Laboratory astrophysicist and project scientist for NASA’s contribution to the Euclid mission, looks forward to examining those galaxies lensed by dark matter. Most of those distant, distorted galaxies merely appear as tiny smudges, less clear than today’s new image of IC 342. But together their impact on dark matter physics will be important, he says: “We’re overwhelmed by the sheer scale of the data, having the fine angular resolution and also the wide field of view. I think we’re going to be drowning in data for years to come.” That resolution is three to five times sharper than what can be achieved by telescopes on the ground, he points out. And while the image resolution is lower than the JWST’s, Euclid surveys large areas 100 times faster.
Like the JWST, Euclid glimpses celestial objects from a spot called the L2 Lagrange point at a distance of about 1.5 million kilometers beyond Earth’s orbit. After the probe reached its destination in late July, engineering teams at ESA’s mission control conducted a long list of tests, calibrating the instruments and ensuring that they will work as planned. On July 31, they released raw test images of fields of galaxies, which hinted at what’s to come.
Then, in August, they encountered issues with the telescope’s fine guidance sensors, which are designed to deliver a precise and stable pointing direction. Those optical sensors are meant to image the sky on the sides of the visible-wavelength instrument’s field of view, but when cosmic rays hit the detectors, they intermittently lost track of guide stars, celestial landmarks used for imaging and navigating. After updating and uploading new flight software, the engineering team determined that they had the problem under control. The issue slightly delayed the team’s progress, but they do not anticipate any further effects on the mission, Bernardeau says.
For now, the Euclid team is continuing their instrument calibration work, and then the telescope’s science mission will begin in earnest in January. Next year they’ll release data from the first 50 square degrees of surveying, followed by the first year’s data. By that time, they’ll finally have scanned enough of the sky to release not just images, but new cosmology research.
