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Nemesis (hypothetical star)

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Nemesis is the name given to a theoretical companion star or brown dwarf orbiting the Sun at a distance of about 50,000 to 100,000 AU, somewhat beyond the Oort cloud.

Nemesis' existence was proposed in a theory put forward by Richard A. Muller to explain an apparent 26-million year cycle in the occurrence of mass extinctions on Earth noted by Raup and Sepkoski.

According to the theory, Nemesis periodically (roughly every 26 million years), passes through a denser region of the Oort cloud, disrupting the orbits of comets, and sending millions into the inner solar system and potential collision with the Earth.

No direct evidence for Nemesis has been found, and the existence of a periodicity in the Earth's series of mass extinctions is disputed.

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