The European Space Agency's Euclid space telescope has captured the largest and most detailed visible-light image of the center of the Milky Way galaxy, known as the galactic bulge.
The image, a mosaic composed of multiple exposures, contains over 60 million stars and is intended to support the detection and study of exoplanets using the gravitational microlensing technique.
Image Details and Acquisition
The image was created from observations conducted on March 23, 2025, over a period of approximately 26 hours. The mosaic covers an area of the sky larger than the full moon and consists of nine separate pointings. The final composite is a 60-gigapixel image with a resolution more than a thousand times that of a typical smartphone photo. The region is located about 26,000 light-years away in the constellation Sagittarius.
Euclid’s visible light camera has sensitivity comparable to the Hubble Space Telescope but covers an area approximately 270 times larger per observation. Its space-based position allows it to avoid atmospheric interference.
Scientific Context and Exoplanet Detection
The galactic bulge is a dense region containing old, cool stars, making it a prime target for detecting exoplanets via gravitational microlensing. This technique relies on the chance alignment of two stars: the gravity of a nearer star bends and brightens the light from a more distant background star. If the nearer star hosts a planet, the planet's gravity adds a small, measurable change in brightness.
No new microlensing events were captured during the 26-hour observation, as detecting them typically requires about 20 days of continuous monitoring. However, the data provides a baseline measurement of stellar positions and motions. This can be used to identify host stars for future microlensing events and to confirm the masses of exoplanets.
The image includes 51 known planetary systems and the host stars of two known cold exoplanets: OGLE-2005-BLG-390Lb (an icy planet) and OGLE-2013-BLG-341Lb (a two-star, one-planet system). The data may allow for precise mass measurements of these planets.
The Euclid telescope was primarily designed to study dark energy and dark matter by creating a 3D map of the universe, and was not originally designed to observe densely crowded star fields. Modifications required extensive simulations and coordination.
Relationship to the Nancy Grace Roman Space Telescope
The Nancy Grace Roman Space Telescope, a NASA mission expected to launch in the future, is scheduled to observe the same region for longer periods to detect microlensing events. Euclid’s images provide a past time reference, allowing astronomers to measure stellar motion and potentially improve the confirmation and mass determination of exoplanets found by the Roman telescope. Euclid’s data can improve microlensing measurements by up to a factor of three.
Context of Known Exoplanets
As of the date of this report, approximately 6,000 exoplanets are known. Microlensing is particularly suited for detecting planets that are colder and farther from their host stars than those found by other methods.