Free Astronomy Magazine September-October 2026

45 SEPTEMBER-OCTOBER 2026 ASTRO PUBLISHING destined to roam the galaxy all alone. “When Roman finds them, as- tronomers will be able to cross-refer- ence Euclid’s earlier observations to look for stars near the lensing object, so we can confirm whether a planet is truly rogue or just orbiting very far from its host star,” said David Ben- nett, a senior research scientist and microlensing expert at the Universi- ty of Maryland, College Park and NASA’s Goddard Space Flight Center. Scientists will also pair Euclid data with Roman’s Galactic Plane Survey. This observation program will reveal our home galaxy in unprecedented detail over an area about 400 times larger than the galactic bulge sur- vey. In one month of observations spread across two years, the Roman survey will unveil tens of billions of stars and explore previously un- charted structures. It’s tricky to study our own galaxy because it’s like trying to map the human body from inside a cell; there’s a lot of stuff in the way. Com- bining Euclid’s observations with Roman’s will let astronomers watch stars slowly move across the sky. Since stars in different parts of the Milky Way tend to follow different paths, this will help astronomers fig- ure out which part of the galaxy those stars are in. “One of the most exciting aspects of the Euclid obser- vations is that they give us the chance to test and improve Milky Way models,” Penny said. Euclid’s one-day detour offers a sci- entific payout that will last for years and shows how much more can emerge when telescopes team up. “We’ve shown that these two tele- scopes can work together to do sci- ence that surpasses what either was originally designed for,” Rhodes said. “In doing so, we’ve established a model for future coordinated ob- servations that can unlock far more discoveries than either mission could make alone.” T his image by ESA’s (European Space Agency) Euclid (with color added using ground-based images) provides an earlier snapshot of a region of our galaxy that NASA’s Nancy Grace Roman Space Telescope will repeatedly observe during the upcoming years. Euclid spent one day taking a series of nine individual images near the heart of the Milky Way. Its wider image has resolution similar to Roman’s, though it’s also shallower and lacks some of the colors Roman will see. At the right of the frame, Euclid looks through the dense foreground of the Milky Way’s galactic plane, where thick molecular clouds appear as dark patches that obscure parts of the galactic bulge beyond. Toward the left, the view rises to higher galactic latitudes: the yellow glow of the bulge becomes clearer, with fewer and more isolated foreground clouds interrupting the starlight. [ESA/Euclid/Euclid Consortium/NASA, CFHT, image processing by J.-C. Cuillandre and E. Bertin (CEA Paris-Saclay)] like a star, planet, or black hole — any object with suf- ficient gravity — closely aligns with a background star from our vantage point. Light from the distant star curves as it travels through the warped space-time caused by the nearer ob- ject’s mass. If the alignment is especially close, the nearer object acts like a cosmic lens, focusing and magnifying light from the background star. “Most often, the lensing object is another star,” said Matthew Penny, an assistant professor at Louisiana State Universi- ty, and co-lead of Euclid’s exoplanet science working group who has spent more than a decade simulating both Euclid and Roman data. “But Roman will also be a- ble to detect planets orbit- ing them, and all kinds of weird objects that are nearly impossible to find any other way.” Among those strange ob- jects are black holes left be- hind after the most massive stars die. Astronomers think there should be about 100 million of these stellar-mass black holes in the Milky Way, but so far they’ve almost exclu- sively detected the invisible objects when they interact with a compan- ion star. Yet most are thought to wander the galaxy alone. Roman will find them even when there’s noth- ing nearby to reveal their presence. While microlensing events created by planets are typically hours or days long, black holes pack in so much mass that they can bend light over a larger region of space, creating much longer signals. That means as- tronomers may need to observe them for years to see the objects move out of alignment. “The extra two years provided by Euclid give astronomers more time to watch the lens and source star drift apart, making it easier to iden- tify the lens and measure its mass,” said Himanshu Verma, a postdoc- toral researcher at Louisiana State University who has been analyzing Euclid images to help scientists pre- dict and better understand the mi- crolensing events Roman is expected to observe. While most planet-hunting methods are best at finding scorching worlds tightly hugging their host star, mi- crolensing is better at detecting worlds in orbits larger than Earth’s. That includes planets that whirl around their stars farther away than Neptune orbits the Sun and ones that have been kicked out of their original star systems altogether, now !