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No direct evidence for Nemesis has been found, however, and the existence of a periodicity in the Earth's series of mass extinctions is disputed.
It is also worth noting that Matese and Whitman have suggested that the cycle might be caused by the solar system oscillating across the galactic plane. These oscillations may lead to gravitational disturbances in the Oort cloud with the same proposed consequences as the orbit of "Nemesis".
However, the period of oscillation is not well-constrained observationally, and may differ from the needed 26 million years by as much as 40%.
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