It is within arcseconds of the Alpha Centauri system, so the first thought is of course that it might be another star within that system. The problem is that the flux detected by the ALMA radio telescopes, and the distance to Alpha Centauri, implies that it would be a red dwarf star easily visible by optical telescopes and just barely visible to the naked eye. No such star exists at that location though!

The authors of the discovery paper then considered other possibilities, that it is an object in our solar system. What it is would then depend on how far away it is. With only two detections with the ALMA array so far we can’t solve for the orbit yet, assuming that it is a solar system object at all. It could hypothetically be a brown dwarf at Oort cloud distances (20,000 AU, not light years as the Forbes article on this erroneously states), but if so it should have been detected by WISE. The authors speculate that perhaps the glare from Alpha Centauri hid it and prevented its detection if that is the case.

If it were a closer solar system object it could be a distant super-earth, similar to what was proposed to be constraining the arguments of perihelia of extreme trans-neptunian objects. In that case it could be something along the lines of a planet 1.5 times larger than earth and 300 AU away, farther than any currently observable trans-neptunian object and too dim to detect with optical or even infrared telescopes.

Source: Archeology Hub