[ThinkPlease]

There is a much derided theory that the Sun has a distant companion that is responsible for causing these eccentric orbits and for intermittent waves of comets that crash into the inner solar system. If I read this report correctly, that theory is a bit more plausible now since something odd is now recognized to be at work in the distant reaches of the Kuiper belt and OOrt cloud.

Yes, the reason that the theory is derided is that there is no place left for a companion to hide. With the advent of all-sky infrared surveys, we've looked everywhere there is to look. As an object big enough to do that kind of damage would radiate pretty brightly in the IR, it's definite that there is no stellar companion orbiting the Sun of anything nearing even the size of Uranus out there.

[Rockingham]

So we are assured. But given the derision that attaches to the theory, I doubt that any search for Nemesis has been energetic and comprehensive. There are far better uses for scarce viewing time and far more plausible theories to pursue -- but the Oort cloud and Kuiper belt are too poorly understood for us to exclude the possibility that they contain one or more massive objects.