THE DEATH STAR THEORY
In 1986, David M. Raup and J. John Sepkoski, Jr. published a paper presenting a statistical model for mass extinctions and underlined the prominence of a periodicity of 26 million years. The two men postulated that there exists a tenth planet or a dark star in the nether regions of our solar system. Nicknamed Nemesis, this planet/star passes through the Oort cloud every 26 million years, causing orbits of the comets in the cloud to be perturbed and sending some of them into the inner regions of our solar system. Some of these comets reach Earth and impact our planet every 26 millions years.
The Death Star theory hopes to explain why there have been so many meteorite impacts on Earth and what is the reason behind the periodicity of these impacts. It is a complimentary theory to the impact theory for it supports the cause of the extinction to be a meteorite impact.. It is a purely theoretically constructed mathematical model without much scientific data backing it up.