The Nemesis theory postulates that there is a small dark star orbiting the sun about 95,000 AU* away.
Nemesis, every twenty six million years, jostles a few of the ten billion comets orbiting in the Oort Cloud causing a few to dislodge and come careening earthward. This suggests that one of these comets could collide with earth causing an extinction event. The rise of mankind could only have happened if the dinosaurs were removed, it is theorized that a comet dislodged from the Oort Cloud by Nemesis could have hit the Earth 63 million years ago. Should we be concerned that Earth could be hit by a dislodged comet this time removing humanity?
The paleontologists claim that, over the last 250 million years, life on Earth has faced extinction in a 26-million-year cycle. Astronomers proposed comet impacts as a possible cause for these catastrophes.
A PLOT OF DATA ON LIFE EXTINCTIONS
Humanity itself could owe its existence to this star's periodic relatively close orbit to the Oort Cloud. Nemesis is probably a red dwarf, the most common type of star in the galaxy (three-fourths of all the stars in the Milky Way are believed to be red dwarfs). Less than a third the size of the sun and about one one-thousandth as bright, Nemesis might travel in an elliptical orbit that at its perihelion (closest point) brings it within a half light year of the sun (one light year is about six trillion miles) and into the midst of the Oort Cloud. Right now, Nemesis may be at its aphelion (most distant point), nearly three light years away. The sun's closest known neighbor, Proxima Centauri, is about 4.25 light years distant.
Stars with less mass than the Sun are smaller and cooler, and hence much fainter in visible light. Brown dwarfs have less than eight percent of the mass of the Sun, which is not enough to sustain the fusion reaction that keeps the Sun hot. These cool orbs are nearly impossible to see in visible light, but stand out when viewed in infrared. Their diameters are about the same as Jupiter's, but they can have up to 80 times more mass and are thought to have planetary systems of their own.
Size comparison of our Sun, a low mass star, a brown dwarf,
Jupiter, and Earth.
*AU astronomical Unit - about the distance from the Earth to the Sun 93 million miles. Making Nemesis 95,000 times that distance away. About 8,835,000,000,000 miles (eight trillion,eight hundred thirty five billion miles)