Sun's neighboring star?

Nemesis is a controversial hypothetical red dwarf/brown dwarf star that orbits the sun from very far away, even farther than the Oort cloud. It is sometimes called "Sun's Death Star." We think that there is this star because we have found a cycle of mass extinctions, occurring every 26 million years or so, that are somehow connected to this star. Still, scientists were unable to prove that Nemesis exists. Does this mean that we might have a binary star system?