On October 25th, 2021, NASA has found evidence of a planet in our star system but outside the Milky Way Galaxy. The planet is about 28 million light-years away and the size of Saturn. It was discovered in the whirlpool galaxy also known as the Spiral Galaxy Messier 51. This intriguing discovery was found using NASA’s Chandra X-ray Observatory.
Astronomers have found other exoplanets such as this one but they have all been inside the galaxy. Rosanne Di Stéfano, who led the study, searched for dips in the brightness of the X-rays received from X-ray bright binaries. They were looking to detect transits that block or all of the X-ray emissions because regions that produce bright X-rays are relatively small. Therefore this exoplanet could be detected from far away. This binary system has a black hole or neutron star orbiting a companion star with a mass about 20 times that of the Sun. Because of the size of the exoplanet as well as the large orbit it has, it would not cross in front of the star or black hole for another 70 years. "And because of the uncertainties about how long it takes to orbit, we wouldn't know exactly when to look," a co-author of the study, Nia Imara, an assistant professor at the University of California, Santa Cruz. The researchers will look in the archives of Chandra and XMM-Newton for more exoplanets in other galaxies. Also being added is a line of research is to look for X-ray transits in Milky Way X-ray sources to discover new nearby planets.