Infographic explaining Euclid’s galactic bulge survey

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.

Read more about this image here.

[Image description: The image is a composite infographic set against a black background. At the top are three rectangular panels arranged from left to right. The left panel shows a bright horizontal band with a bright central area. The middle panel shows a spiral pattern viewed from above, with a white rectangular outline marking a region. The right panel shows a zoomed-in spiral view labelled ‘Solar System’. Behind these panels, a wide background image filled with densely packed yellow and gold points of light spans most of the width. Along the bottom centre, four numbered rectangular cutouts are shown in a row, each highlighting a different close-up region with varying colours and densities. On the far right, an additional rectangular panel shows a broader view with several numbers marking the locations of the cutouts within it.]

Technical details:

The Euclid galactic bulge survey was conducted in early 2025 using Euclid’s optical camera VIS (monochromatic, one colour). These are first and foremost Euclid images, defined by Euclid’s crisp resolution and spectacularly wide field of view; the colours 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 colours 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 colours. Subtle differences in optical design of the two telescopes become apparent for the brighter objects.