I'm putting this here, because there's no proof nemesis exists or 2012 will kill us all.
2012 is supposedly armegeddon, Nostradamus predicted it (although his predictions also continue until the 38th century) the Mayans predicted it (although only because their calendar stops there, which is reasonable considering they made it 5000 years ago. it also marks the end of the 13th b'ak'tun, but mayans belived 12 had gone before, so more will probably come after)
there have also been dozens (thousands!) of scenarios for the end of the world. one of which is the idea of Nemsis, a distant star with which our sun is in a binary orbit with.
This is largely discredited, mainly due to the obvious flaw that there are no nearby stars that we can detect. (meaning there are no nearby stars)
However I saw a program, and found out about these
http://www.patricktaylor.com/146
Wandering black holes....
Black holes are undetectable (hence the 'black') except by the telltail signs as it consumes nearby matter. Black holes are also basically material objects, so are affected by gravity.
Since it's rightly shown there are no nearby stars. how would we detect a black hole in the four lightyear gap between us and the nearest star? It's also possible (assuming they were as super advanced/alien aided as the myths say) that the mayans could have seen this black hole as it passed by the distant stars five millenia ago.
Could nemesis be a wandering black hole? even one as small as a football could destroy the earth if it came too close.