One of the most interesting topics I've been watching. WISE, a satellite telescope designed to see cold, dark objects moving in space that would not be visible to a normal telescope, is looking for just that. Something big, big enough to affect planets orbits and their angular momentum. Something heavy and dense, dark and cold, as mentioned here, possibly a brown dwarf star. Fascinating stuff. This was also the reason for the establishment of the LUCIFER telescope with the Vatican/Univ. of Arizona as joint participants. Keep watching...
Still waiting for the appearance of this "second sun"....
