Nemesis

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Nemesis is a hypothetical companion star of our Sun. It is believed to be found some 50,000 to 100,000 AU. That puts it a little farther than another hypothetical entity in the Universe – the Oort cloud. If the idea that brought forth Nemesis has any truth, then these two may have had something to do with the extinction of the dinosaurs some 65 million years ago.

The idea of Nemesis’ possible existence sprouted from what some paleontologists described as the cyclical nature of extinction rates. According to David Raup and Jack Sepkoski, they were able to observe an average interval between major extinctions (like the one that wiped out the dinosaurs).

This interval was estimated to be about 26 million years. Over a span of 250 million years, about 12 extinction events were identified by Raup and Sepkoski. Coincidentally, two of the twelve events were identified to be times when large impact events caused by celestial objects happened.

The two paleontologists were only able to point out the cyclical nature of the extinctions. They were not however able to point out the causes.

This is where astronomy comes into the picture. The prevailing theory as to what caused the dinosaur’s extinction had something to do with an asteroid striking planet Earth. Astronomers Whitmire, Jackson, Davis, Hut, and Muller suggested the possibility of the Sun having a companion star.

This star, they proposed, was located near the Oort cloud and was capable of causing disturbance there at certain specific instances during its (the star’s) orbit. The disturbances may have caused the Oort cloud to launch more comets than usual, with some of them colliding with our planet and its neighbors (the Moon included).

The star was eventually named Nemesis. Nemesis, if it really exists, is believed to be a red dwarf or a brown dwarf. That our star, the Sun, can possibly have a companion star is not an entirely unique concept. In fact, many of the stars in the Universe have companions stars. They are known as binary star systems.

Many of the stars that are observed to be burning very brightly are already identified as binary star systems. Because of their great distance from us, it is difficult for the two to be distinguishable. They simply appear as one when viewed through the naked eye.

Such star systems have been detected through either optical, spectroscopic, or astrometric techniques.

Astronomical surveys like the Pan-STARRS or LSST may be used to find Nemesis.

Want to read more about the Oort cloud? Here are some articles from Universe Today:
Oort Cloud
Where do comets come from?

Tired eyes? Listen to some episodes at Astronomy Cast. Here are two that might interest you:

Stellar Roche Limits, Seeing Black Holes, and Water on Mars
The Search for Extraterrestrial Intelligence

Reference:
NASA Ask an Astrophysicist

Tagged as: binary star, comet, Nemesis, Oort cloud