At least one in a dozen stars shows evidence of planetary ingestion.

Stellar chemical compositions can be altered by ingestion of planetary material and/or planet formation, which removes refractory material from the protostellar disk. These 'planet signatures' appear as correlations between elemental abundance differences and the dust condensation temperature. Detecting these planet signatures, however, is challenging owing to unknown occurrence rates, small amplitudes and heterogeneous star samples with large differences in stellar ages.

Rapidly rotating second-generation progenitors for the 'blue hook' stars of ω Centauri.

Horizontal branch stars belong to an advanced stage in the evolution of the oldest stellar galactic population, occurring either as field halo stars or grouped in globular clusters. The discovery of multiple populations in clusters that were previously believed to have single populations gave rise to the currently accepted theory that the hottest horizontal branch members (the 'blue hook' stars, which had late helium-core flash ignition, followed by deep mixing) are the progeny of a helium-rich 'second generation' of stars. It is not known why such a supposedly rare event (a late flash followed by mixing) is so common that the blue hook of ω Centauri contains approximately 30 per cent of the horizontal branch stars in the cluster, or why the blue hook luminosity range in this massive cluster cannot be reproduced by models.

The remnants of galaxy formation from a panoramic survey of the region around M31.

In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound stars surrounding the galaxy, at distances that reach 10-100 times the radius of the central disk. The number, luminosity and morphology of the relics of this process provide significant clues to galaxy formation history, but obtaining a comprehensive survey of these components is difficult because of their intrinsic faintness and vast extent.