Euclid’s Milky Way View Previews NASA Roman Core Survey

ESA’s Euclid mission has captured a high-resolution preview of the Milky Way’s galactic bulge to provide a baseline for the upcoming NASA Nancy Grace Roman Space Telescope. According to NASA, this coordinated effort allows astronomers to extend the Roman telescope’s future survey by two years, improving the detection of isolated black holes and rogue planets through gravitational microlensing.

Coordinating Euclid and Roman for Galactic Mapping

Euclid paused its primary cosmology survey for one day in March 2025 to image a 5-square-degree region near the heart of the Milky Way. Jason Rhodes, a senior research scientist at NASA’s Jet Propulsion Laboratory in Southern California and the U.S. Euclid science lead, stated that this snapshot will be integrated with the Roman telescope’s future Galactic Bulge Time-Domain Survey.

While Euclid’s image is shallower and lacks some of the color detail the Roman telescope will eventually capture, it provides a wider view—roughly the area of 25 full moons. Roman will later focus on a smaller, 1.7-square-degree area, imaging it repeatedly to track changes in hundreds of millions of stars.

Detecting Rogue Planets and Isolated Black Holes

Astronomers use a phenomenon called microlensing to find “invisible” cosmic objects. This occurs when the gravity of a massive object, such as a planet or black hole, bends and magnifies the light of a distant background star. According to Matthew Penny, an assistant professor at Louisiana State University, this method allows the detection of objects that are nearly impossible to find via other means.

The collaboration between the two telescopes is specifically designed to identify two types of elusive objects:

• Stellar-mass black holes: Scientists believe 100 million of these exist in the Milky Way. Himanshu Verma, a postdoctoral researcher at Louisiana State University, notes that Euclid’s data gives astronomers more time to watch the lens and source star drift apart, making it easier to measure the black hole’s mass.
• Rogue planets: These are worlds that have been ejected from their star systems. David Bennett says Euclid’s observations help confirm if a planet is truly rogue or simply orbiting its host star at a great distance.

Comparison of Survey Capabilities

Overcoming the ‘Inside-Out’ Mapping Challenge

Mapping the Milky Way is difficult because interstellar dust and molecular clouds obscure the view. Euclid’s imagery shows these clouds as dark patches on the right side of the frame, while the yellow glow of the galactic bulge becomes clearer toward the left at higher latitudes.

By combining Euclid and Roman data, astronomers can track the movement of stars across the sky. Because stars in different galactic regions follow distinct paths, this data allows scientists to refine models of the Milky Way’s structure, according to Matthew Penny.

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