Nemesis is the nickname of a theorhetical and highly
controversial companion
star to our
Sun. It is
thought to be a small, dim dwarf, orbiting the Sun in
an
elliptical orbit, with a
period of 25 - 30 million years.
The theory behind this star is the apparent extinction of
large amounts of animal species, which seem to happen every 26 million years, according to David Raup and
John Sepkoski at the University of Chicago. The most
recent of these eradications took place 11.3 million years
ago. Michael Rampino, using a different analysis, found this period to be 30 million years.
The basic idea behind the theory is that Nemesis, in
it's passing, disturbs the Oort Cloud surrounding our
solar system, and as a result, thousands, perhaps
millions of comets will be sent out of their orbit,
tumbling towards the Sun.
There is much controversy surrounding the alleged
extinction theories, and very few researchers take
them seriously. The main argument against
it is that this star and our Sun would interact so
weakly that other stars around us would jerk it
out of its orbit. Also, numerous searches for
large nearby objects have been conducted, and the
largest detected so far has only 10 times the mass
of Jupiter.