We might have just discovered first planet beyond our galaxy; 28 million light-years away

NASA's Chandra X-ray Observatory for the first time has identified an exoplanet outside of the Milky Way galaxy. Astronomers have found hints that the temporary dimming of X-rays may be a planet passing in front of a neutron star or black hole.

“Chandra scientists have found the first possible planet candidate outside of our galaxy! Located about 28 million light years from Earth in galaxy M51, it's thousands of times farther away than all the other exoplanets detected in our Milky Way,” the Chandra X-ray Observatory tweeted on Monday.

The possible exoplanet candidate was spotted in the spiral galaxy Messier 51 (M51) and is located some 28 million light-years away from the Milky Way, the Observatory said in a statement.

According to the Chandra X-ray Observatory, this new discovery is based on transits, where the passage of a planet in front of a star blocks some of the star's light and yields a characteristic dip in brightness that can be detected by telescopes. This general technique has already been used to find thousands of exoplanets.

For this study, astronomers used Nasa's Chandra X-ray Observatory and the European Space Agency's XMM-Newton space telescope to look at three galaxies beyond the Milky Way.