No, we don't think so.

The Nemesis Star was suposed to be a distant companion of the Sun in a 26 million year orbit. It would perturb comets in the Oort CLoud and send thousands of them into the inner solar system where some would collide with Earth and produce mass extinctions.

It was proposed for non-astronomical reasons to explain the seemingly periodic extinction record every 26 million years. Since this was proposed over two decades ago, the basis for the claim has evaporated, as has the need for a star to cause extinctions in the way that was imagined.

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