Cosmic doomsday

sudden flash of increased brightness on the Sun, usually observed near its surface and in close proximity to a sunspot group

flashes of gamma rays from distant galaxies

hypothetical star orbiting the Sun, responsible of extinction events

collision of two astronomical objects with measurable effects

hypothesized extended period of worldwide cold weather due to the impact of a celestial body on the Earth's surface

supernova that occurs close enough to the Earth to have noticeable effects on its

biological contamination of a planetary body by a space probe or spacecraft