A collision between our Milky Way galaxy and its largest neighbor, the Andromeda galaxy, predicted to occur in about 4.5 billion years, has been anticipated by astronomers since 1912.

Once seen as inevitable within 10 billion years, the odds are now a coin flip — and the sun will expand to engulf Earth billions of years earlier anyway.

For over a decade, researchers have suggested a high possibility of our Milky Way galaxy smashing into neighboring galaxy Andromeda around 5 billion years from now. The collision would merge the ...