Joint press release ASI-INAF-INFN
The ESA Euclid mission, thanks to the VIS instrument developed with the contribution of the Italian Space Agency (ASI), has obtained the largest and most detailed image ever made of the centre of the Milky Way in visible light. Teeming with over 60 million stars, this image of our galaxy will allow scientists to confirm the existence of extrasolar planets found in this region and to measure their mass using tiny variations in starlight over time.
Rome, 24 June 2026 – Between 23 and 24 March 2025, in approximately 26 hours, the Euclid space telescope captured a large and extremely detailed map of the centre of our galaxy. It is a mosaic of nine “pointings” of its visible-light camera, each of which covers a portion of sky larger than the full Moon.
For a single day, our dark-Universe detective, Euclid, therefore averted its gaze from the distant galaxies it usually studies, turning it towards the extremely bright central region of the Milky Way, known as the galactic bulge, managing to distinguish individual stars without its detectors becoming saturated. This special request came from astronomers who wanted what Euclid does best: capturing enormous portions of sky with extremely sharp detail, in this case in order to study exoplanets, planets orbiting stars other than the Sun, using a special technique called microlensing.
Capturing enormous portions of sky with extremely sharp detail is precisely one of the characteristics of the European Euclid probe. For comparison, Euclid’s sharpness and sensitivity in visible light are similar to those of the wide-field camera of NASA/ESA’s Hubble Space Telescope, but each pointing Euclid captures in just a few hours covers an area 270 times larger than Hubble’s field of view. To observe the same mosaic as Euclid, a large ground-based observatory such as Keck, in Hawaii, would require around 2,000 hours. Euclid is faster and capable of capturing details of fainter stars that would otherwise be lost when observing from the ground. The portion of sky observed was chosen because it also includes the entire region that the future Roman Space Telescope will monitor in the search for extrasolar planets.
To do this, Euclid uses the VIS camera (Visible Instrument), one of the two scientific instruments on board, designed to observe billions of distant galaxies and built under UK leadership, but with an important contribution from Italy. The National Institute for Astrophysics (INAF) and national industry, with funding and coordination from ASI, were responsible for the design and construction of the hardware and software of the VIS control electronics: this is the heart of the instrument that enables the sending and receiving of commands and collects data, preparing them for transmission to the ground.
“The observation of the galactic bulge was a complex operation,” reports Andrea Zacchei, INAF research director and head of Euclid’s ground segment. “Euclid has two highly sensitive instruments on board designed to probe the faintest objects in the universe; to observe the bulge we had to switch off the infrared camera because its sensors would have been overexposed, causing a persistence effect that would have compromised subsequent observations for several days. A team of experts also developed a dedicated analysis pipeline, given the peculiarity of the observation.” The work involved many Italian researchers who successfully contributed both to the planning of the measurements, demonstrating their feasibility, and to the reduction of the data and finally to their important scientific analysis.
In these images Euclid captured more than 60 million stars, together with nebulae and star clusters. This densely populated region of our galaxy is the perfect place for astronomers to search for exoplanets using microlensing, a particular form of gravitational lensing. While Euclid mainly uses gravitational lensing, described by Einstein’s theory of general relativity, to explore massive and distant objects such as galaxy clusters, or the distribution of dark matter, this new image of the galactic centre helps scientists study on an infinitesimal scale the lenses produced by stars and exoplanets in our galaxy.
Microlensing is based on the random alignment of two stars with an observer. When two stars lie along the same line of sight, the nearer star acts as a cosmic magnifying lens, bending and amplifying the light from the background star. If a planet orbits the nearer star, the one acting as the lens, the planet’s gravity also contributes to the bending of this light, producing a small anomaly. This tiny variation in brightness is what reveals the presence of a planet. To observe a microlensing event, a telescope should study a star for more than twenty days, that is, for the time necessary to characterise the anomalies in the deflected light caused by the planet as it orbits its star. Therefore, in Euclid’s observations, lasting just one day, it is not possible to detect new events, but what makes this image so special is that it allows scientists to measure the mass of already known planets located in this region, as well as that of planets yet to be discovered.
In the last twenty years, almost 300 exoplanets have been discovered using this technique, all with ground-based telescopes and all located towards the centre of our galaxy. A study led by Valerio Bozza of the University of Salerno within the Euclid Consortium identified in this Euclid image 51 already known planetary systems; the data released today will be extremely useful for studying the many other exoplanets that will be discovered.
“Microlensing is one of the most elegant effects of Einstein’s general relativity: mass curves spacetime and bends light, turning stars and planets into cosmic lenses. Euclid is able to observe this phenomenon with unprecedented precision, making it an extremely powerful tool for studying our galaxy as well,” emphasises Stefano Dusini, INFN researcher.
Euclid is one of the most ambitious projects of ESA’s Science Programme, in which Italy, through ASI, INAF and INFN, plays a leading role involving more than two hundred Italian scientists, also belonging to numerous universities, including the University of Bologna, the University of Milan, the University of Genoa, the University of Trieste, SISSA, the University of Ferrara, the University of Turin, and CISAS of the University of Padua.
In addition to the VIS camera, Euclid’s other eye, the Near Infrared Spectrometer Photometer (NISP), was also built by a consortium of European institutions funded by national space agencies with a strong Italian contribution. ASI, in collaboration with INAF and INFN, led the industrial team that designed and built contributions to both instruments, consisting of a Temporary Association of Companies with OHB Italia as lead contractor, SAB Aerospace and Temis as partners, while ESA entrusted the construction of the satellite to Thales Alenia Space Italia of the Leonardo group. ASI is also funding the industrial activities, assigned to ALTEC in Turin, supporting the mission’s Italian Science Data Centre, located at the INAF site in Trieste. Finally, Italy played a fundamental role in designing the mission’s observational strategy and today coordinates all ground data processing activities.
The next milestone for Euclid is the new data release scheduled for November 2026, which will make available to the entire scientific community observations of a much larger extragalactic region of sky (around 2,000 square degrees), providing data ready for detailed studies in various branches of astronomy and cosmology. Elisabetta Tommasi, ASI manager for Euclid activities, recalls that “the release of data to the scientific community is possible thanks to the immense work of that part of the mission’s ground segment, led by Italy, which, by developing dedicated software for the analysis of Euclid data and managing nine Data Centres across Europe, is able to process and distribute data usable for scientific analysis.”
In the meantime, the Euclid scientific community is working tirelessly to extract from the observations information on the role of dark matter and dark energy in the evolution of the Universe, which are the main objectives of the mission; the publication of Euclid’s first cosmological results, together with the first complete data release, is expected in mid-2027.
