So far, all the “observable” planets and exoplanets referenced by scientists come from the same place in the universe: our Milky Way (a galaxy among billions of others…). The astrophysicist Rosanne Di Stefano, from the Center for Astrophysics | Harvard & Smithsonian (CfA) in Cambridge (Massachusetts / USA) believe they have found the trace of the very first extragalactic planet. The latter would be located in the spiral galaxy Messier 51 (M51), which also bears the pretty nickname of the Whirlpool galaxy and which is located 27 million light years from Earth.
A study published in the scientific journal Nature Astronomy details the technique used for the detection of this first extragalactic planet. Rosanne Di Stefano reviewed the stellar luminosity potentially caused by the repeated passage of a planet in front of its star, based on readings from NASA’s Chandra Observatory. The latter records in particular the reductions in the luminosity of X-rays sometimes generated by binary systems.
The binary system that interests the researcher is here composed of a neutron star or a black hole “sucking” the gas from its star, which generates a burst of heat … producing X-rays. A planet passing in front of this X-ray production zone could therefore theoretically “shield” (from the observer’s point of view).
In the supposed zone of the first extragalactic star detected, the researcher and a team of astronomers thus noted a decrease in the intensity of the X-rays over a period of 3 hours, which could well be the sign of the passage of a planet . Scientists have already ruled out the hypothesis of another type of “body” obstructing X-rays (such as a gas cloud for example). Other observations will undoubtedly make it possible to confirm the discovery, but it will be necessary to be very patient: the calculation of the elliptical trajectory of the supposed extragalactic planet indicates that its next passage in front of the zone of emission of the X-rays will occur from here … 70 years.