The hunt for exoplanets goes beyond the Milky Way. Astronomers using NASA’s X-ray Observatory Chandra have discovered what the first signs of a planet in another galaxy might be. The team noticed a drop in X-ray brightness that suggests the transit of the planet in front of a star in the galaxy Messier 51 (aka M51) 28 million light-years away. For context, not all candidates for the Milky Way exoplanets are more than 3,000 light-years from Earth – this planet would easily set a distance record if confirmed.
The very nature of the stars made this feat possible. As the researchers had to focus on binary X-ray systems where the light beam area is relatively small, transit was much easier to spot. Conventional detection of nearby stars requires much more sensitive light detection, because a planet can block only a small amount of light from a given star.
The planet itself is believed to be as big as Saturn, but it would orbit its hosts (a star 20 times the mass of the Sun, as well as a black hole or a neutron star) at twice the distance.
Scientists did not believe that the blackout was caused by gas clouds or dust because they were not in line with the event they recorded in M51. The planet, however, would align with the data.
The challenge is, as you can guess, to verify that data. The planet’s large orbit could rule out another transit in about 70 years, and it would not be clear when astronomers will have to look. The three-hour transit of candidates for this planet did not provide a large window. This also under the assumption that the ‘living’ star does not explode and bathes the planet with radiation.
However, if there is ever confirmation, the discovery would be very significant. Although there is little doubt that planets exist in other galaxies, it would be useful to have evidence of their existence. This could also significantly expand the scope of future planetary searches to include a galactic neighborhood, not just nearby stars.
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