LONDON — Billions of years from now, the Sun will exhaust its hydrogen fuel and enter what astronomers call the 'giant branch' phase. The Sun will grow bigger by hundreds of times, while its luminance and radiation output increase by thousands of times.

Writing in the Monthly Notices of the Royal Astronomical Society, researchers say this energy will heat up the asteroid belt and cause the asteroids to spin faster and faster until they are torn to pieces, which will happen in six billion years.

Since most big asteroids are a loose collection of rocks called rubble piles, they are susceptible to this heat induced spinning, or the YORP effect. Most asteroids will be reduced until they become small homogeneous fragments.

The scientists' model predicts that the Sun will collapse into a white dwarf and absorb the smashed asteroids, which pollutes the star and changes its spectra. This would explain why many white dwarfs' spectra suggest the dead stars contain asteroid elements.