Europe’s Euclid space telescope has delivered the largest high-resolution visible-light image yet released of the Milky Way’s central bulge, offering a rare view into one of the most crowded and difficult regions of the night sky. Captured on 23 March 2025 and released in June 2026, the Euclid Milky Way galactic bulge image combines nine successive pointings made over roughly 26 hours. The finished mosaic covers 4.8 square degrees more than 20 times the apparent area of the full Moon — and resolves more than 60 million stars.
The achievement is notable not only for the scale of the image, but also for its scientific purpose. Euclid was built primarily to investigate dark matter and dark energy by observing billions of distant galaxies. Yet its brief diversion towards the inner Milky Way has created a valuable reference dataset for gravitational microlensing, a technique that can detect planets around other stars through subtle changes in starlight. The observation therefore links a European cosmology mission to future exoplanet research led by NASA’s Nancy Grace Roman Space Telescope.
Milky Way’s crowded heart: a 26-hour survey of 60 million stars
The galactic bulge is the dense, central concentration of stars surrounding the Milky Way’s nucleus. Looking towards it from Earth means observing through the crowded foreground of the Galactic plane, where dust, gas and millions of intervening stars complicate almost every measurement. In visible light, thick molecular clouds obscure sections of the bulge, creating dark filaments and patches that can appear empty but in fact block the light of more distant stellar populations.
Euclid’s new mosaic reveals this layered environment in exceptional detail. It includes dark molecular clouds, glowing emission nebulae, young stellar groupings and the yellowish light of older, cooler stars concentrated towards the inner Galaxy. The image also contains star clusters, including NGC 6451, an open cluster roughly 8,700 light-years from Earth. Together, these features illustrate that the central Milky Way is not a uniform field of stars, but a dynamic overlap of stellar generations, gas structures and dust lanes.
The European Space Agency’s Euclid release describes the result as the largest and most detailed visible-light image yet made of the Galactic centre. Its importance lies in the number of individual sources that can be separated in a region where conventional surveys often face severe confusion: neighbouring stars overlap, and a faint object can be hidden within the glare of a brighter one.
Euclid was able to distinguish millions of individual stars because it combines a sharp optical system with a broad field of view. The survey used the spacecraft’s visible-light instrument, known as VIS, which produced the original monochrome images. Colour was added later using observations obtained in 2025 with the Canada-France-Hawai‘i Telescope’s MegaCam instrument. The resulting public image is therefore a combination of Euclid’s sharp visible-light data and ground-based colour information.
Why Euclid’s wide field changes the scientific value of the image
The decisive feature of Euclid is not simply image sharpness, but the combination of sharpness and coverage. Its visible-light resolution is comparable to that of Hubble’s wide-field camera, while each Euclid pointing covers an area around 270 times larger than Hubble’s field of view. That difference matters when the scientific objective is to map a crowded stellar region rather than to examine a single galaxy, nebula or cluster.
Ground-based observatories can obtain extremely detailed images, but Earth’s atmosphere limits their ability to resolve faint stars consistently across large areas. According to ESA, reproducing Euclid’s bulge mosaic with the Keck Observatory would require around 2,000 hours of observing time. Euclid completed the required coverage in about one day, making the dataset an example of how a wide-field space observatory can complement narrower but more specialised facilities.
This efficiency is particularly valuable for stellar population studies. A mosaic of this scale can be used to investigate how stars are distributed across different parts of the bulge, how dust changes the apparent brightness of background objects, and how stellar motions vary between the Galactic disc and the central regions. It also creates a reference image of a field that will be observed repeatedly by Roman, allowing scientists to compare earlier and later measurements over a multi-year baseline.
The French space agency CNES notes that the image demonstrates Euclid’s ability to combine a very large observing field with high spatial resolution. This is significant because Euclid’s nominal mission is cosmological: its main survey is designed to map the shapes, distances and motions of billions of distant galaxies. The galactic bulge observation shows that the same technical capabilities can produce major results closer to home.
Gravitational microlensing: a time reference for exoplanet research
The principal scientific use of the Euclid Galactic Bulge Survey is gravitational microlensing. The method depends on a chance alignment between two stars along the same line of sight. When a foreground star passes closely in front of a more distant background star, the foreground star’s gravity bends and magnifies the background star’s light. The temporary brightening can be measured from Earth or from space.
A planet orbiting the foreground star may create a short additional disturbance in this light curve. That small deviation can reveal the planet’s presence, its approximate mass and its separation from the host star. Unlike the transit method, which is especially effective for planets orbiting close to their stars, microlensing can detect planets at wider orbital distances. It is therefore particularly well suited to cold planets, including worlds on orbits comparable to or larger than Earth’s, as well as free-floating planets that may no longer orbit any star.
Euclid’s observation was too short to discover a complete microlensing event on its own. Planetary microlensing signals normally require repeated monitoring over days or weeks, while longer events involving massive objects such as black holes can continue for years. However, the snapshot provides something else: a record of the stars in the field before future lensing events occur.
This earlier reference point will be especially useful for NASA’s Roman Space Telescope, which is expected to conduct a long-term Galactic Bulge Time-Domain Survey. Roman will repeatedly monitor six fields covering 1.7 square degrees, observing hundreds of millions of stars at high cadence. By comparing Roman’s future images with Euclid’s 2025 view, astronomers can measure how quickly potential lens stars and background source stars separate over time.
That motion is critical. Once the lens and source can be distinguished, researchers can better establish whether the signal was caused by a planet and constrain the planet’s mass. As NASA’s Roman mission team explains, Euclid effectively extends Roman’s observational baseline by around two years, giving astronomers more time to study the changing positions of stars involved in future microlensing events.
Cold planets and rogue worlds in a crowded Galactic field
Microlensing offers one of the few practical ways to study planets in colder, wider orbits across the Milky Way. Such planets are difficult to identify with transit surveys because they pass in front of their host stars only rarely, and they are difficult to detect through radial-velocity measurements because their gravitational pull produces smaller, slower stellar motions.
The method can also help distinguish between distant planets on very wide orbits and genuinely rogue planets. A microlensing event alone may reveal a planetary-mass object, but it does not always show whether that object has a distant host star. Euclid’s pre-event images can assist astronomers in examining the local stellar environment around the lens and assessing whether a host star is present.
This is why the mosaic has value beyond its visual impact. It is an astrometric archive: a detailed positional and photometric reference for future events. The longer the time interval between Euclid’s image and Roman’s observations, the more likely it becomes that the source and lens stars can be separated sufficiently to improve mass measurements.
Europe and France: the infrastructure behind Euclid’s science return
Euclid is a European Space Agency mission, built and operated by ESA with contributions from NASA and the international Euclid Consortium. Thales Alenia Space served as prime contractor for the satellite and service module, while Airbus Defence and Space developed the payload module, including the telescope. NASA supplied the detectors for Euclid’s Near-Infrared Spectrometer and Photometer, known as NISP.
France has played a central role in the mission’s scientific and technical architecture. The CNES supports French laboratories involved in the VIS and NISP instruments and is responsible for operating the Euclid ground segment. CNES also provides one-third of the mission’s global computing capacity and supervises the processing chain that transforms the spacecraft’s vast stream of observations into usable scientific products.
The bulge image itself reflects this French contribution. Processing was led by Jean-Charles Cuillandre and Emmanuel Bertin at CEA Paris-Saclay, while the colour information was provided through the Canada-France-Hawai‘i Telescope. This combination of spacecraft observation, international ground-based data and European processing infrastructure illustrates the distributed nature of modern space astronomy.
According to the CNES Euclid mission overview, around 40 French laboratories are involved in the wider programme. Their participation extends beyond the public image release: it includes instrument development, data analysis, scientific interpretation and the computational systems required to handle an archive designed to support astronomical research for decades.
From dark Universe mission to Galactic observatory
Euclid’s principal objective remains cosmological. Over its six-year mission, the telescope is expected to map a substantial fraction of the sky and observe billions of galaxies out to roughly 10 billion light-years. The data will be used to study the evolution of cosmic structure, the distribution of dark matter and the accelerating expansion of the Universe associated with dark energy.
Yet the galactic bulge observation demonstrates the wider scientific reach of such a mission. A telescope designed to study the large-scale Universe can also contribute to research on brown dwarfs, binary stars, dust structures, stellar motions and planetary systems within the Milky Way. Euclid’s large field and stable space-based imaging make it an effective bridge between cosmology and Galactic astronomy.
The value of the bulge survey will grow as Roman begins its repeated observations. Euclid has not replaced Roman’s infrared, high-cadence capability, and Roman will be able to probe dusty central regions that visible-light observations cannot penetrate as effectively. But Euclid has supplied the earlier image, wider context and positional baseline that will help Roman’s future detections become more informative.
Euclid’s view of the Milky Way is therefore more than a record-breaking astronomical image. It is a carefully timed scientific reference that turns a one-day interruption to a cosmology survey into a long-term asset for exoplanet science, stellar dynamics and the study of the Galaxy’s crowded central regions.
