Astronomers may have just found the first ever planet outside of our Milky Way Galaxy. This possible exoplanet, which has been named M51-ULS-1b, is located about 28 million light-years away from us in a spiral galaxy known as Messier 51 (M51) – also called the Whirlpool Galaxy.
Astronomers were observing three galaxies by using NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton space telescope when they made the discovery. Specifically, they observed 55 systems in the Whirlpool Galaxy; 64 systems in Messier 101 (M-101) – also known as the Pinwheel Galaxy; and 119 systems in Messier 104 – also called the Sombrero Galaxy.
While looking at the Whirlpool Galaxy, the scientists found an object passing in front of a star, blocking its light for a short amount of time (this is called a transit). The transit lasted approximately three hours. In fact, they specifically looked for dips in the luminosity of the stars’ X-ray emissions as explained in a statement by Rosanne Di Stefano who is an astrophysicist at the Harvard-Smithsonian Center for Astrophysics and who led the study, “We are trying to open up a whole new arena for finding other worlds by searching for planet candidates at X-ray wavelengths, a strategy that makes it possible to discover them in other galaxies.” The X-ray emissions that they observed went all the way down to zero.
They made this discovery in a binary system that is orbiting two large space objects that are either a neutron star or a black hole that is orbiting a gigantic companion star.
Based on their observations of the transiting time and the X-ray emission dips, the team estimated that the potential exoplanet was approximately the same size as Saturn. This object orbits the neutron star (or possibly a black hole) about twice the distance that Saturn orbits our sun.
Interestingly, the object will not transit in front of the star again for another 70 years or so. “Unfortunately to confirm that we're seeing a planet we would likely have to wait decades to see another transit,” noted Nia Imara who is a researcher at the University of California at Santa Cruz, adding, “And because of the uncertainties about how long it takes to orbit, we wouldn't know exactly when to look.”
While M51-ULS-1b hasn’t officially been called a planet (they need to gather more data first), if it is confirmed, it would be the first ever discovery of an exoplanet outside of our galaxy and could open doors for potentially finding other worlds in distant galaxies. The fact that astronomers were able to detect an object 28 million light-years away from us is absolutely mind-blowing. An artist’s impression of a neutron star near a black hole in the Whirlpool Galaxy can be seen here.
Their study was published in the journal Nature Astronomy where it can be read in full.