Key points from article :
A collision with a giant comet would be cataclysmic.
The odds of another such catastrophe have remained uncertain.
Astronomers have performed a risk assessment on the Oort cloud.
19 to 24 stars will come close enough to deflect comets in the next million years.
Not all dislodged comets would hit Earth.
The study was published in the Astronomy & Astrophysics journal.
