Euclid mosaic of the Milky Way galactic bulge showing an extremely dense field of stars in visible light. The image is dominated by countless tiny points of starlight against black space, with several bright star clusters and darker dust lanes visible. Credit: ESA/Euclid/Euclid Consortium/NASA, CFHT, image processing by J.-C. Cuillandre and E. Bertin (CEA Paris-Saclay).
Euclid's view of the Milky Way's galactic bulge, the densest region of our galaxy. The image is a mosaic of nine pointings captured by the telescope's visible light camera over 26 hours on March 23, 2025. Each pointing covers a patch of sky larger than the full Moon. Credit: ESA/Euclid/Euclid Consortium/NASA, CFHT, image processing by J.-C. Cuillandre and E. Bertin (CEA Paris-Saclay).

In March 2025, the European Space Agency's Euclid space telescope did something it was never built to do. Designed to map billions of distant galaxies and probe the invisible forces shaping the universe, it turned instead toward the brightest, most crowded part of our own galaxy. For 26 hours, it stared at the Milky Way's center.

The result, released June 24, 2026, is the largest and most detailed visible-light portrait of the galactic core ever made. More than 60 million individual stars fill a single mosaic. Fifty-one known planetary systems sit inside the frame. And for astronomers hunting worlds beyond our solar system, the image changes everything.

A telescope with two lives

Euclid launched in 2023 on a 1 billion euro mission to build the most accurate 3D map of the cosmos. Its job is to measure how dark energy and dark matter have shaped the distribution of galaxies across cosmic time. The telescope's visible light camera, called VIS, was built for that dark universe survey, not for taking pictures of bright stars in our own galaxy.

Zoomed-in view of the Euclid galactic bulge image showing thousands of individual stars as distinct points of light, with several brighter stars and star clusters visible against the dense stellar background
A zoomed-in vignette covering just 0.003 percent of the total survey area. Even in this tiny patch, thousands of individual stars are distinguishable. Across the full 4.8-square-degree mosaic, Euclid charted more than 60 million stars. Credit: ESA/Euclid/Euclid Consortium/NASA, CFHT, ESA/Gaia/DPAC, image processing by J.-C. Cuillandre and E. Bertin (CEA Paris-Saclay).

But that same camera has a rare skill. Its sensitivity in visible light is comparable to Hubble's Wide Field Camera, yet each pointing it captures spans an area 270 times larger than Hubble's field of view. To observe the same patch of sky, the Keck Observatory on Mauna Kea would need roughly 2,000 hours. Euclid did it in 26.

"It was never built with this science in mind, but it has proved to be a superb facility for the work," said Eamonn Kerins, an astrophysicist at the University of Manchester's Jodrell Bank Centre for Astrophysics.

The crowded heart of the galaxy

The region Euclid observed is the galactic bulge, a dense, bar-shaped structure at the center of the Milky Way made mostly of old, cooler stars packed together far more tightly than the spiral arms where our Sun lives. From Earth, the bulge appears as a brilliant band of light in the constellation Sagittarius, but its true structure is hidden behind thick lanes of interstellar dust.

Euclid's visible light camera can see through enough of that dust to resolve individual stars, something few telescopes can manage in such a crowded field. The result is a mosaic made from nine separate pointings, each one covering more sky than the full Moon. Stitched together, they form a single 4.8-square-degree portrait of the galaxy's most densely populated neighborhood.

Infographic showing the location of Euclid's galactic bulge survey within the Milky Way, using data from ESA's Gaia mission. The survey area is highlighted against a full-sky map of the galaxy
The Euclid galactic bulge survey covers a 4.8-square-degree region at the center of the Milky Way, shown here on a full-sky map from ESA's Gaia mission. Credit: ESA/Euclid/Euclid Consortium/NASA, CFHT, ESA/Gaia/DPAC, image processing by J.-C. Cuillandre and E. Bertin (CEA Paris-Saclay).

Why 60 million stars matter

The image is beautiful, but its scientific purpose is specific. Astronomers want to use it for microlensing, a technique that relies on the chance alignment of two stars with an observer on Earth.

When one star drifts in front of another, the nearer star's gravity bends the light of the more distant one, making it appear brighter. If a planet orbits the nearer star, its gravity adds a tiny extra tug to the light, creating a distinctive spike in brightness. The pattern reveals the planet's presence and, critically, allows astronomers to measure its mass.

"To catch microlensing, you need to observe parts of the sky that are crowded with stars, such as close to the centre of our galaxy," said Jean-Philippe Beaulieu of the Institut d'Astrophysique de Paris, who originally pushed for Euclid to observe the galactic bulge. "During the last twenty years, almost 300 exoplanets have been discovered using this technique, all with ground-based telescopes and all towards the centre of our galaxy."

This single Euclid image already includes 51 known planetary systems. And it will do more than just photograph them. Because Euclid captured the stars before any microlensing alignment occurs, the image serves as a baseline. When future telescopes, particularly NASA's Nancy Grace Roman Space Telescope launching this August, detect microlensing events in the same region, astronomers can compare the overlapping stars to Euclid's earlier snapshot.

"This means that anyone who detects a microlensing event in the same region will be able from now on to use Euclid data as a time reference in the past," said Natalia Rektsini, who led the data release of the galactic bulge survey. "Since Euclid can clearly separate individual stars, one can then measure how fast they move over time and use that information to confirm the existence of a planet and determine its mass."

A preview of what Roman will do

The timing is no coincidence. NASA's Roman Space Telescope, scheduled for launch no earlier than August 30, 2026, will scan the same region of the galactic bulge for microlensing events. Roman is expected to discover roughly 1,500 microlensing exoplanets over its primary mission. The Euclid image covers the entire area Roman will monitor, providing a before picture taken more than a year before any of those events happen.

"The Euclid snapshot will improve those measurements possibly by up to a factor of three, which for a single image is quite something," Kerins said.

Roman's data will also help address one of the big unknowns in exoplanet science: the population of cold, icy planets. Most planet-hunting techniques favor large, hot worlds close to their stars. Microlensing is different. It finds whatever is out there, regardless of the planet's temperature or the brightness of its host star. The technique is uniquely sensitive to cold exoplanets in the outer reaches of their solar systems, worlds that other methods routinely miss.

One day of Euclid time

The image was taken on March 23, 2025, during a single 26-hour observation window. Euclid has spent most of its mission surveying distant galaxies, but its ability to cover large areas of sky at high resolution makes it uniquely suited for this kind of bonus science. The same quality that lets Euclid map the dark universe at unprecedented speed also lets it produce the sharpest wide-angle portrait of our own galaxy's core.

"This data fires the starting pistol in a new age of exoplanet discovery, where we go from knowing about 6,000 exoplanets to finding more than 100,000 across the galaxy," Kerins said.

The image and its associated data are publicly available through the ESA Euclid archive and the ESASky science portal. The data covers not just the visible light shown in the mosaic, but also near-infrared measurements that can help astronomers distinguish between different types of stars and understand the structure of the galactic bulge itself. More than just a pretty picture, it is a reference frame for a generation of exoplanet science to come.

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All images are from ESA/Euclid/Euclid Consortium/NASA, CFHT, with image processing by J.-C. Cuillandre and E. Bertin (CEA Paris-Saclay). These images are publicly released under ESA's standard image use policy (CC BY-SA 3.0 IGO) and may be used with proper attribution.

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