Saturday, September 26, 2009
It is widely known that a majority of stars have companions. These so-called binary star systems seem to be the norm rather than the exception throughout the universe. A persistent question in astronomy has been why the Sun (our star) is not in a binary system? That is a matter of opinion according to Richard Muller, Professor of Astronomy at UC Berkeley. Muller hypothesizes that the Sun actually does have a companion, a red dwarf star he’s named “Nemesis”.
The Nemesis theory was originally published in Nature by Davis, Hut, and Muller (vol 308, pp 715-717, 1984). The theory was created to account for the regularity of mass extinctions on Earth with a periodicity of 26 million years. According to the theory, a binary companion to the Sun in a highly elliptical orbit perturbs the Oort comet cloud every 26 million years causing comet showers in the inner solar system. A comet striking the Earth would cause mass extinctions. Nemesis is thought to orbit the Sun at a distance of 50,000 to 100,00 AU (astronomical units, the distance of the Earth to the Sun). Muller believes that Nemesis is currently 1-1.5 light years away.
Nemesis is most likely a red dwarf with a magnitude between 7 and 12. There are roughly 3,000 candidate stars in consideration for Nemesis. There are several all sky surveys underway (Pan-STARRS and LSST) that should confirm or rule out the existence of Nemesis in the next several years. So it is just a waiting game to see if our Sun has a sibling.