Protoplanetary disks
Protoplanetary disks are the main sites of planet formation. The are found around young stars, and contain the necessary building blocks to form planetary systems. They are essentially a by-product of star formation: when stars form in collapsing cores of molecular clouds, angular momentum prevents all the gas and dust to end up on in the star. It ends up orbiting the new-formed star, forming a protoplanetary disks. The disk is dispersed in a few million years, setting the timescale for planet formation.
Observations of disks are plenty. However challenging, they can be imaged directly in scattered starlight, in thermal mid-infrared emission or with interferometers at (sub)-millimeter wavelengths to study their geometry. With mid and far infrared spectroscopy we can study the composition and evolution of dust, as well as trace some of the gas that governs the disk dynamics. Additionally, broad-band spectral energy distributions of large numbers of disks are available, allowing for characterizations of protoplanetary disks at different stages of their evolution.
Research on this topic in Amsterdam is mostly focussed on Herbig Ae and Be stars, young stars of 2-8 solar mass. Because they are more luminous, their disks can be studied in great detail. The recent discovery of giant planets orbiting main-sequence A stars supports the interpretation that these disks are forming planets, similar to their sun-like counterparts, T-Tauri stars. The signposts of planet formation, such as the appearance of disk gaps and growth of dust grains, can be identified in these disks and be used to study the first stages of planet formation.
Fig. 1: Artist impression of planet formation in a protoplanetary disk. credit: David Hardy
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