Pasquini and his colleagues circumvented this difficulty by examining stars at a later stage of development. Such so-called red giants arise when a star like the sun runs out of fuel. In the last phase of their lives, the aging light bulbs inflate into a huge ball of fire.
Strangely enough, red giants with planetary systems contain less iron and other heavy elements than their precursor stars. Pasquini and his colleagues explain it this way: In a normal star, only about two percent of the stellar mass in the outermost layer, the so-called convection zone, is mixed. Dust and debris from planetary formation remain trapped in this layer for billions of years. Only when a star turns into a red giant, the planetary debris is strongly diluted: in the convection zone, then about two-thirds of the star material is stirred.
"The simplest explanation for the data is that sun-like stars appear metal-rich because their atmospheres are contaminated, " explains co-author Artie Hatzes of the Thüringer Landessternwarte in Tautenburg. His colleague Luca Pasquini adds: "The anomaly simply disappears when the stars flare up to become red giants." DisplayLuca Pasquini (European Southern Observatory, Garching) et al .: Astronomy & Astrophysics in press Ute Kehse