The star Beta Pictoris shows off its dust halo in this infra-red image. J.-L. Beuzit et al. Habing and colleagues studied stars that were as far as possible 'normal', avoiding any that were variable in brightness or were components of multiple-star systems. By using observations at three wavelengths of infrared light, they determined which stars were circled by dust. Therefore, most of these discs lasted about 300-400 million years before fading away.
Calculations suggest that dust particles remain in stellar discs for less than one million years.
Small dust particles are pushed away by the star's radiation, while larger ones are slowed down by the impact of solar wind particles and spiral into the star. The most likely explanation is that material is added to them during their lifetimes and that the discs dissipate when the source of material is exhausted. Habing and colleagues calculate that a typical disc would require about 40 times the mass of the earth to be added to it over its lifetime. Two mechanisms could supply this dust - collisions between larger objects and the evaporation of comets as they pass close to the star. Habing and colleagues point out possible links with events in the beginnings of our own Solar System.