First-ever planet may have been found in another galaxy

First Candidate for a Planet in an External Galaxy

In a surprise paper, a team of researchers from the U.S. and China has found the first evidence for a candidate planet in another galaxy.

The planet candidate lies in the M51 Whirlpool Galaxy and is approximately 23 million light years away. M51 lies relatively close to Ursa Major aka the “Great Bear”. The researchers observed what they believed to be planetary transit that lasted for approximately three hours as seen in figure 1 below.

Abstract:

Do external galaxies host planetary systems? Many lines of reasoning suggest that the answer must be ‘yes’. In the foreseeable future, however, the question cannot be answered by the methods most successful in our own Galaxy. We report on a different approach which focuses on bright X-ray sources (XRSs). M51-ULS-1b is the first planet candidate to be found because it produces a full, short-lived eclipse of a bright XRS. M51-ULS-1b has a most probable radius slightly smaller than Saturn. It orbits one of the brightest XRSs in the external galaxy M51, the Whirlpool Galaxy, located 8.6 Megaparsecs from Earth. It is the first candidate for a planet in an external galaxy.

The paper: https://arxiv.org/pdf/2009.08987

If it is confirmed, it will be named M51-ULS-1b.

More analysis of the system is required before the object can be confirmed as an actual planet revealed by a planetary transit, but if confirmed as a planet, the researchers believe it will likely be approximately the size of Saturn or a little smaller.