This infographic places Euclid’s galactic bulge survey in the broader context of the Milky Way’s structure, using data from ESA’s Gaia mission.
The top row shows schematic views (artist impressions) of our spiral galaxy: an edge-on view highlighting the central bulge (top left), a top-down view revealing the spiral arms and the survey region (top centre), and a zoom into the galactic disc indicating the location of the Solar System (top right), from where Euclid observes the sky, which turns into the main background of the visual.
The lower panel illustrates the diversity of objects captured by Euclid as it observed towards the galactic bulge in March 2025. Moving from left to right, the numbered cutouts highlight dense molecular clouds that obscure background starlight, a glowing emission nebula associated with recent star formation, a young star cluster, and finally the galactic bulge itself – a dense, spheroidal region containing ten billion stars. This crowded central region provides ideal conditions for detecting microlensing events.
Cutout 1 shows an area of the observations of the galactic bulge, made by the European Space Agency’s Euclid space telescope. A dense molecular cloud in the foreground, called LDN 10, obscures the light from the galactic bulge (yellow).
Cutout 2 shows an area of the observations of the galactic bulge, made by the European Space Agency’s Euclid space telescope. An emission nebula, known as G000.583-00.870, is visible in red. This nebula is a cloud formed of ionised gases that were send out by massive stars that recently formed in a spiral arm of the Milky Way.
Cutout 3 shows an area of the observations of the galactic bulge, made by the European Space Agency’s Euclid space telescope. Here the open star cluster NGC 6451 is visible, 8700 light-years away from us.
Cutout 4 shows an area of the observations of the galactic bulge, made by the European Space Agency’s Euclid space telescope. The galactic bulge – the central region of our galaxy – is a vast, tightly packed structure filled mainly with old, cooler stars, giving it its characteristic yellow color.
Technical details: The Euclid galactic bulge survey was conducted in early 2025 using Euclid’s optical camera VIS (monochromatic, one color). These are first and foremost Euclid images, defined by Euclid’s crisp resolution and spectacularly wide field of view; the colors were added using observations captured in the summer of 2025 with the Canada-France-Hawai'i Telescope’s MegaCam camera (CFHT-Megacam) in Hawai’i. The colors captured by MegaCam are in optical light through three broad-band filters (u, g, and r) overlapping the very broad VIS band over the r-band. The appearance of the most luminous stars in these images looks different than those generated from Euclid-only images, with additional diffraction spikes and a subtle halo around the very bright stars. This a consequence of combining Euclid VIS data, for their sensitivity and sharpness, and CFHT-MegaCam for the colors. Subtle differences in optical design of the two telescopes become apparent for the brighter objects.
