Using NASA's Chandra X-ray Observatory, a team of scientists managed to detect the first exoplanet, a planet orbiting stars outside the solar system, outside of our galaxy, BBC reports. The exoplanet is said to be located in the Messier 51 (M51) galaxy at a distance of 28 light-years from the Milky Way, and it can be compared to Saturn in terms of its size.
Exoplanets are usually detected using the transit method: a planet revolves around its star and passes right in front of it at some point, changing its brightness, which makes it possible for scientists to detect it.
However, it is almost impossible to observe transits in the visible spectrum at intergalactic distances. Therefore, scientists led by Dr. Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics looked for changes in the brightness of X-rays from a binary system M51-ULS-1, a star system containing a neutron star or a black hole that pull the gas from an orbiting companion star. The material near the black hole or neutron star heats up and begins to glow in X-rays. When passing in front of the binary star, the exoplanet blocks most X-rays, making its transit easy to spot.
The exoplanet's transit lasted three hours. Scientists calculated that it orbits a star at a distance of about two astronomical units. Astronomers have already found about 5,000 exoplanets, but all of them are located within our galaxy, the Milky Way.
This discovery is yet to be confirmed by other scientists. They need more data to validate the interpretations of this observation, which will be difficult to do in the coming years since the exoplanet takes about 70 years to complete a revolution. The detected object might also be a cloud of interstellar dust, but astronomers think this is less likely.