NASA’s Chandra X-ray Telescope has found evidence of what might be the first planet to be discovered outside of our Milky Way galaxy. The possibly detected signal is in the Messier 51 galaxy, about 28 million light years from Earth. NASA’s Chandra Observatory was designed to detect X-ray emissions from very hot regions such as exploded stars, galaxy clusters, and matter around black holes. It recently discovered a characteristic decrease in brightness that occurs when a planet passes a star and blocks some of its light. This method has helped astronomers discover thousands of “exoplanets” – worlds orbiting stars beyond the sun.
The research was carried out by Dr. Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics in Cambridge and her colleagues. Using ground-based and space-based telescopes, the astronomers looked for “breaks in optical light, electromagnetic radiation that humans can see and that enable the discovery of thousands of planets,” says a press release.
Because a potential planet the size of the X-ray source around the neutron star or black hole is close, a planet moving along Earth’s line of sight could temporarily block most or all of the X-rays. In the most recent observation, the transit took about three hours, during which the X-ray emission dropped to zero. So the astronomers estimate that the candidate planet would be about the size of Saturn.
“The method we developed and used is the only currently feasible method for discovering planetary systems in other galaxies,” said Dr. Di Stefano of the Harvard-Smithsonian Center for Astrophysics in Cambridge, USA, told BBC News.
The researchers admit that what they found may be a planet, but more data and more study are needed to be sure. A challenge here is that the candidate planet has a large orbit. This means that after 70 years the object would cross its binary partner again. Another possible explanation for the ingress of light could be clouds of gas and dust. The researchers looked at this explanation, but then concluded that it was unlikely because other features were inconsistent with such an event.