VILNIUS, LITHUANIA – In a groundbreaking discovery, astronomers have identified a rare exoplanet located at the very edge of the Milky Way galaxy, utilizing a method rooted in Albert Einstein’s theory of general relativity. This extraordinary finding, published in the journal Astronomy & Astrophysics in May 2025, marks a significant advancement in the exploration of distant exoplanets and their environments.
Breaking: Discovery of AT2021uey b
The planet, named AT2021uey b, was discovered using gravitational microlensing, a phenomenon that occurs when the gravity of a massive object, such as a planet, bends and magnifies the light from a star behind it. This method, grounded in Einstein’s theory, allows astronomers to detect planets that would otherwise remain invisible.
AT2021uey b resides approximately 3,200 light-years from Earth and orbits a small, dim star, making this finding all the more extraordinary.
Immediate Impact on Planetary Formation Theories
AT2021uey b’s position at the edge of the Milky Way is significant for several reasons. As a Jupiter-sized gas giant, it is only the third planet discovered in such a distant region of the galaxy. This area is relatively sparse in heavy elements, which are thought to be necessary for planet formation.
The discovery suggests that planets might form in places previously thought unsuitable, offering new insights into planetary formation models. This could lead astronomers to rethink the way planets are created and evolve in various environments across the galaxy.
Key Details Emerge
The planet orbits an M dwarf star, a relatively cool and small star, once every 4,170 days—approximately 11 years. The star itself is about half the temperature of the Sun, making it much less luminous than our familiar solar system’s star.
This discovery challenges traditional models of planetary formation, showing that gas giants like AT2021uey b can exist in places far removed from the galactic center.
The Role of Gravitational Microlensing
What truly sets this discovery apart is the method used to detect AT2021uey b: gravitational microlensing. This technique involves observing a momentary increase in a star’s brightness, which happens when the gravitational field of a planet distorts space-time, acting like a magnifying lens on the star’s light.
The Gaia space telescope first spotted the microlensing event in 2021, when the planet’s shadow caused a brief brightening in the star’s light. This method requires precise alignment of the star and the planet, and only a small percentage of stars show the microlensing effect.
Expert Analysis
“This kind of work requires a lot of expertise, patience, and, frankly, a bit of luck,” commented study co-author Marius Maskoliūnas, an astronomer at Vilnius University in Lithuania. “You have to wait for a long time for the source star and the lensing object to align and then check an enormous amount of data.”
Challenging Existing Models
AT2021uey b’s discovery pushes the boundaries of current planetary formation models. For years, scientists have thought that gas giants like Jupiter should only form closer to their stars, where the conditions are warmer and conducive to the accumulation of large amounts of gas.
Edita Stonkutė, the leader of the microlensing project, explained the implications of this finding:
“When the first planet around a sun-like star was discovered, there was a great surprise that this Jupiter-type planet was so close to its star. As data accumulated, we learned that many types of planetary systems are completely unlike ours — the solar system. We’ve had to rethink planetary formation models more than once.”
What Comes Next
This insight suggests that the formation of planets, particularly gas giants, may occur in ways that are vastly different from the patterns observed in our own solar system. The discovery of planets like AT2021uey b challenges conventional understanding and opens new doors for the study of distant worlds in the universe.
As astronomers continue to explore the outer reaches of our galaxy, discoveries like AT2021uey b will undoubtedly contribute to a deeper understanding of the universe and its myriad planetary systems.