Exoplanet hunting is expanding beyond the Milky Way. NASA's Chandra X-ray Observatory has detected signs that a planet might exist in another galaxy. The team observed dips in Xray brightness that suggested that a planet was transiting in front a star in Messier 51 (aka M51), galaxy 28 million light years away. If confirmed, the distance record for exoplanet candidates within the Milky Way is only 3,000 light years from Earth.
This feat was possible due to the very nature of stars. The transit was much easier to spot because the researchers had only to concentrate on X-ray bright binary system where the area of bright rays are relatively small. Because a planet may only block some light from a star, conventional light detection requires much greater light detection.
It is thought that the planet would be twice as big as Saturn. However, it would orbit its hosts (20 times the mass of the Sun) at twice as far as the Earth.
Scientists did not believe that the dimming was caused by gas clouds or dust. These are inconsistent with M51's event. However, a planet would match the data.
As you might expect, the challenge is in verifying this data. Because the planet orbit is large, it could prevent another transit for approximately 70 years. Astronomers wouldn't know when to look. This planet candidate's three-hour transit didn't offer a wide window. This is also true assuming that the 'living star' doesn't explode and flood the planet with radiation.
The confirmation would be significant if it ever happens. Although there is no doubt that planets exist within other galaxies it would be helpful to have proof of their existence. This would allow future planetary searches for evidence to expand beyond the local stars and include the galactic neighbourhood.
