A new window opens to planets in other galaxies
In short: Until recently, every exoplanet ever discovered resided within our own Milky Way. That changed with a detection in the Whirlpool Galaxy, a feat made possible by shifting our gaze from visible light to the high-energy world of X-rays.
Astronomers have detected potential signs of a planet transiting a star in the M51 galaxy, also known as the Whirlpool Galaxy. Located in the constellation Canes Venatic, M51 is approximately 28 million light-years from Earth. This discovery is significant because nearly all previously known exoplanets were found within our own galaxy, typically at distances of less than 3,000 light-years. To achieve this, researchers led by Rosanne Di Stefano utilized NASA’s Chandra X-ray Observatory.
While traditional missions like Kepler and TESS look for dips in optical light—the radiation humans can see—this new strategy targets X-ray bright binaries. These are luminous systems where a neutron star or black hole pulls gas from a companion star, superheating the material until it glows in X-rays. The mechanism relies on the fact that the X-ray-producing region is relatively small.
When a planet passes in front of it, it can block most or all of the X-rays, creating a distinct dip that is much easier to spot than the tiny fraction of visible light blocked by a planet orbiting a normal star. Situated within the M51-ULS-1 binary system, this particular candidate revolves around a secondary star possessing a mass roughly 20 times our Sun's. This breakthrough represents a major shift in the Space Race, moving from local neighborhood exploration to a method capable of identifying worlds across intergalactic distances. By searching at X-ray wavelengths, scientists can now probe a 'whole new arena' for other worlds, potentially revealing the prevalence of planetary systems in the distant universe.
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Sources
- Summary by Intellect · source: What NASA Found Outside Our Galaxy
- Also: First Evidence of a Planet Identified Beyond Our Galaxy - NASA Science
- Also: Chandra Sees Evidence for Possible Planet in Another Galaxy - NASA
- Also: phys.org — Webb telescope discovers hidden planet in famous star system
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