In recent years, astronomers have started to look for exoplanets outside of the Milky Way, and the first one may have been found. Astronomers using NASA’s Chandra X-ray Observatory have detected what might be the first signs of a planet in another galaxy.
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The scientists in the team picked up dips in X-ray brightness that hint at a planet transiting in front of a star in the Messier 51 (aka M51) galaxy 28 million light-years away. As a comparison, all the exoplanets discovered so far are no more than 3,000 light-years away from us.
According to the team, the only reason this observation was possible is because of the inherent properties of stars themselves. Researchers had to focus on X-ray bright binary systems where the region of bright rays is relatively tiny, the transit was considerably easier to spot. It is very different to traditional planet observation in our galaxy, which is based on more light-sensitive measurement techniques. As a result, a planet might only block a small amount of light from a given star.
It is thought that the planet is about the size of Saturn, but it orbits its hosts – a star about 20 times the mass of the Sun and a neutron star or small black hole – at about twice the distance of Saturn from our Sun. Scientists didn’t believe the dimming was due to gas clouds, as those aren’t consistent with the event they recorded in M51. A planet, however, would line up with the data.
The biggest challenge the team faces is verifying the data. The large orbit of the planet means that it will only be able to make another transit for us to measure in about 70 years. The transit in front of the planet only took about 3 hours, so our timing would need to be extremely accurate to confirm it then.
While it is widely accepted that other galaxies will have more or less the same density of planets than the Milky Way, but to be able to confirm at least one will go a long way to confirming it.
