Quote:
Originally Posted by AussieTrooper
None. Zero. Zilch.
Any object large enough to be labelled a star would have been detected long ago.
It is possible that there is another Neptune sized object out there though. Objects with highly elliptical orbits that never come closer than Neptune are the most difficult to discover, due to them spending so much of their orbit so far away, with so little lateral orbit as seen from earth.
The record for the farthest out object discovered gets broken a couple of times each decade, though all these objects are much smaller than any of the 8 recognised planets.
For something the size of Neptune, you're talking perihelion beyond the Kuiper belt. Possibly an object with an orbit perturbed early in the solar system's history. Pure speculation though.
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OK, but if it were a very small star....like a brown dwarf...could it not be possible that it has remained undetected for all of this time and if its orbit is highly elliptical and it approaches its partner star (our Sun) once in every 26,000 years (a time span which has been suggested on a number of websites I've seen), then its presence would be unknown to humanity, because 26K years ago, we weren't really into astronomy ....well nothing that has come down to us, anyway.