Most detailed image of Milky Way shows over 60 million stars

The European Space Agency's (ESA) Euclid space telescope has unveiled the most detailed visible-light image to date of the Milky Way's star-packed galactic bulge. The enormous image features over 60 million stars, as well as numerous stellar clusters and nebulae. This crowded region of our galaxy is the perfect place for astronomers to search for exoplanets using a technique called microlensing.

Microlensing is a form of gravitational lensing that occurs when a massive object passes in front of a more distant star, briefly bending and magnifying the star's light as seen from Earth. The same situation also occurs for any nearby planets, allowing astronomers to identify otherwise invisible subjects. According to Jean-Philippe Beaulieu of the Institut d'Astrophysique de Paris, "To catch microlensing, you need to observe parts of the sky that are crowded with stars, such as close to the center of our galaxy."

The Euclid space telescope captured the enormous photo in 26 hours on March 23, 2025, in a mosaic of nine "pointings" from its visible-light camera, with each pointing covering a patch of sky larger than the full Moon. The telescope's camera is rare in being sensitive enough to separate individual stars in the crowded region known as the galactic bulge. This ability could also help scientists search for exoplanets in the area in a bid to better understand and map our galaxy.

The image includes 51 known planetary systems, and it will assist in studying many more that will be found. As Beaulieu explained, "During the last twenty years, almost 300 exoplanets have been discovered using this technique, all with ground-based telescopes and all towards the center of our galaxy." The Euclid image will transform the work of astronomers searching for exoplanets, as it shows the same stars before they overlap, allowing them to measure how fast they move and to confirm the existence of the planet and its mass.

The Euclid data will serve as a reference point for NASA's Nancy Grace Roman Space Telescope, which will launch in August 2026 and repeatedly observe the galactic bulge in coming years. The Roman telescope aims to spot a further 100,000 exoplanets as they move across the face of their parent stars, causing a slight, momentary dimming of the starlight. The Euclid data will help astronomers to confirm they are transiting planets and not objects such as binary star systems, which can produce similar signals.

The image of the galactic bulge is not only a valuable tool for scientists but also a breathtaking work of art. As Dan Zafra, co-founder of Capture the Atlas, said, "Visually, it has the emotional impact of a great astronomical artwork. Scientifically, every star in the frame is data."