Nemesis (star)

Nemesis is a hypothetical red dwarf or brown dwarf, first thought in 1984M. Davis, P. Hut, and R. Muller, “Extinction of species by periodic comet showers”, Nature 308, 715 (1984). to be orbiting the Sun at a distance of about 95,000 AU (1.5 light-years), past the Oort cloud, to explain a cycle of mass extinctions in the geological record, which look like they happen every 26 million years. In a 2017 paper, Sarah Sadavoy and Steven Stahler said that the Sun was probably part of a binary system when it formed, making them suggest "there probably was a Nemesis, a long time ago". This star would have separated from this binary system more than four billion years ago, meaning it could not be what made the cycle of mass extinctions.

Later, geologists found there was a cycle of extinctions, but it was twice as long. However, in 2011, scientists checked at craters and found there was no pattern. 

There were many attempts to find Nemesis. The Infared Astronomical Satellite, launched in the 1980s, was not able to find it. The 2MASS astronomical survey, which ran from 1997 to 2001, did not see another star or brown dwarf in the Solar System. Using newer and more powerful infrared telescope technology that can find brown dwarfs as cold as 150 kelvins out to a distance of 10 light-years from the Sun, the Wide-field Infrared Survey Explorer (WISE survey) has not found Nemesis.

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Category:Extinction events