By Mia Becker-Hansen | Head of Science and Technology
Astronomers has found hints of what could be the first planet ever to be discovered outside our own galaxy.
Nearly 5000 ‘exoplanets’ have previously been discovered outside of our own solar system, but all inside the Milky Way, within 3000 light-years from Earth. The new discovery is believed to be Saturn-sized, located around 28 million light-years away in the Messier 51 galaxy (the Whirlpool Galaxy), in a binary system called M51-ULS-1.
The new result is based on transits recorded by NASA’s Chandra X-Ray Telescope. Transits are a measure of looking at light from a star being blocked by the passage of an object orbiting in front of it. It looks at a dip in brightness which can be analysed to find the size and shape of the object orbiting the star. This same technique has been previously used to find thousands of exoplanets.
This new study was done by looking at dips in X-rays received rather than light from an object called an X-ray bright binary. These objects are usually made up of a neutron star or a black hole pulling in gas from a nearby companion star. The material near the neutron star or black hole becomes very heated up and glows at X-ray wavelengths, which can be seen by an X-ray telescope.
The region that could be producing these X-rays is small, so a planet passing in front could block most of all of the rays, making the transit very easy to spot.
“The method we developed and employed is the only presently implementable method to discover planetary systems in other galaxies,” said Dr Di Stefano from the Harvard-Smithsonian Center for Astrophysics in Cambridge, US, “It is a unique method, uniquely well-suited to finding planets around X-ray binaries at any distance from which we can measure a light curve.”.
The researchers says that a much larger amount of data is needed to verify their findings. An issue with this is that the orbit of the candidate chosen is so large, it will not pass in front the star for another 70 years. Another possible explanation for the transit could be the presence of gas and dust passing in front the X-ray source, but this seems unlikely as the characteristics of the event do not match up with the properties of a gas cloud.
If the planet does exist, it would have suffered a violent history with more peril to come. Being so close to a neutron star or black hole, it would have had to survive a nearby supernova explosion. The companion binary star could also at some point explode into a supernova, showering this newly found planet with deadly radiation.