Euclid space telescope delivers stunning new view of Milky Way's galactic bulge

At a glance:

• The European Space Agency's Euclid telescope has captured the largest high-resolution image ever made of the Milky Way's galactic center in visible light
• The March 23, 2025 observation, lasting 26 hours across nine pointings from 26,000 light-years away, revealed over 60 million stars
• The stunning image could aid exoplanet discovery through microlensing, featuring 51 known planetary systems

The European Space Agency's Euclid space telescope turned its attention to the heart of the Milky Way for just one day in March 2025, delivering an unprecedented glimpse into our galaxy's bustling core. Launched in July 2023, Euclid is primarily designed to study the dark universe, but on March 23, 2025, it pivoted to capture the bright inner region known as the galactic bulge. The resulting image represents the largest high-resolution photo ever produced of our galaxy's center in visible light, showcasing millions of stars packed together in crystalline detail.

From its vantage point 26,000 light-years away, Euclid stared into the stellar dense core using its visible light camera. The observation campaign lasted 26 hours and was assembled from nine separate pointings, each capturing a patch of sky larger than the full Moon. While Euclid's sharpness and sensitivity rival the Hubble Space Telescope's wide field camera, each of its individual pointings covers an area 270 times larger than Hubble's field of view. This ultra-wide perspective allowed the telescope to reveal more than 60 million stars in crisp detail, including faint stars that ground-based telescopes typically miss.

The galactic bulge itself is populated predominantly by old, cooler stars, giving the region its distinctive yellow hue. These densely packed stellar populations create the perfect conditions for microlensing events—phenomena that Euclid's image is exceptionally well-suited to study. The telescope's visible light camera proved sensitive enough to distinguish individual stars in the super-crowded region without being overwhelmed by the intense stellar density.

Beyond the sea of stars, Euclid's image reveals the galactic bulge's interaction with interstellar matter. The dark patches scattered throughout the visible-light photograph are dense, dust-rich molecular clouds that absorb and scatter light from the bulge behind them. These absorptive features provide valuable information about the chemical composition and structure of the Milky Way's central regions, data that will inform models of galactic evolution.

The image's most immediate scientific value lies in its potential for exoplanet discovery through gravitational microlensing. When a foreground star passes in front of a background star from our perspective, its gravity acts as a cosmic magnifying glass, bending and brightening the distant star's light. If planets orbit the foreground star, their gravitational influence creates telltale distortions in this brightening pattern. Jean-Philippe Beaulieu, an astronomer at the Institut d'Astrophysique de Paris who co-led Euclid's exoplanet working group, emphasized the technique's power: "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."

Microlensing has proven remarkably productive for exoplanet detection, with almost 300 exoplanets discovered using this technique over the past twenty years—all through ground-based telescopes observing toward the galactic center. Euclid's new image already includes 51 known planetary systems and will assist researchers in studying many more. While the single-day observation didn't capture new microlensing events, the dataset provides a crucial time reference for measuring the masses of already-identified planets.

Valeria Pettorino, Euclid's project scientist at ESA, highlighted the broader significance: "In just 24 hours, Euclid has delivered unique data on the Milky Way's centre, with a large and sharp view of this region. With time, the separation between sources and lenses increases. That's why this Euclid data will be a time reference for past and future missions and enable studies of exoplanets and their masses."

The galactic bulge observation demonstrates Euclid's versatility beyond its primary cosmology mission. By capturing this massive stellar collection in such fine detail, the telescope has provided astronomers with a powerful new tool for understanding both the structure of our galaxy and the population of planets beyond our solar system. The combination of Euclid's wide-field capability and high sensitivity creates an ideal dataset for ongoing and future microlensing surveys, potentially expanding our knowledge of planetary systems throughout the Milky Way's crowded central region.