Euclid reveals the largest and most detailed photo of the centre of the Milky Way
With more than 60 million stars, the image could help confirm the existence of exoplanets and measure their masses through variations in starlight
On 24 June, the European Space Agency (ESA) revealed the largest and most detailed photo ever produced of the centre of our galaxy. For just one day, the Euclid space telescope turned its gaze towards an extremely bright and densely populated region known as the galactic bulge.
On 23 March 2025, ESA’s “dark Universe investigator” captured a vast image in just 26 hours, a mosaic combining nine pointings taken with its visible-light camera. Each piece of the mosaic covers an area of sky larger than the full Moon and captures more than 60 million stars, along with nebulae and star clusters.
The image paves the way to confirm the existence of exoplanets in this region of the Milky Way and measure their mass through tiny variations in starlight over time.
Although designed to observe billions of distant galaxies, Euclid’s camera is so sensitive that it can distinguish individual stars in the dense galactic centre without being blinded. With a sharpness similar to that of Hubble (NASA/ESA), it captures in just a few hours a field 270 times larger than its field of view. To achieve the same result from earth, the Keck Observatory, the large astronomical observatory located in Hawaii, would need around 2,000 hours. The mosaic also includes the entire region that NASA’s future Roman telescope will monitor.
Hunting for exoplanets with gravitational microlensing
The study of planets around other stars will be carried out using gravitational microlensing. The technique is based on the perfect chance alignment of two stars: the one in the foreground acts as a cosmic magnifying lens, amplifying the light of the star in the background. If a planet orbits the lens star, its gravity alters this light asymmetrically, revealing its presence. This earth-based method has already made it possible to discover almost 300 exoplanets; Euclid’s map includes 51 known systems and will help to find many more, especially cold, icy planets.
In a single day of observation, Euclid cannot record new planets directly, but it provides a fundamental time reference point in the past. By having photographed these stars before they align, it will allow future missions (such as the Roman telescope) to go back through the data: by comparing images over time, scientists will be able to confirm the existence of the new planets and calculate their mass precisely.
Euclid and the University of Bologna
Launched in July 2023, Euclid began its routine observations in February 2024. The mission’s main objective is to reveal over the next six years the hidden influence of dark matter and dark energy on the visible Universe, by observing the shapes, distances and movements of billions of galaxies up to 10 billion light years away. The mission is managed by the ESA with contributions from NASA and the Euclid Consortium, which brings together over 2,000 scientists from 300 institutes worldwide.
The University of Bologna’s Department of Physics and Astronomy "Augusto Righi" was among the mission’s designers and founders, leading to the development of Euclid. It all began in 2007 with the SPACE (Spectroscopic All-sky Cosmic Explorer) project submitted by an international team led by Prof. Andrea Cimatti as part of the ESA’s Cosmic Vision 2015-2025 space programme.