Dust
The space inbetween the stars is not empty, but filled with a mixture of gas and dust called the interstellar medium (ISM). The ISM in our galaxy contains enough mass to continuously for new stars, while older stars donate mass back to the ISM enriching it with the heavier elements that we find on earth today, but were not present after the Big Bang. Although the dust of the ISM contains only 1% of its mass, it can be observed in the infrared through all stages of its life-cycle.
Dust first forms in the outer layers of dying and evolved stars such as planetary nebulae and AGb stars. It is mixed into the ISM, where it resides as the diffuse ISM or more dense molecular clouds. The latter are also the sites of star formation, completing the life cycle of dust in the ISM. During and after the star formation process, dust can be found in protoplanetary disks - where planetary systems are formed - and in debris disks, the remnants of planet formation.
Through all these stages, the dust can be observed at infrared and submillimeter wavelengths, with space-based telescopes such as Spitzer and Herschel, but also ground-based facilites such as the VLT. The ISM group in Amsterdam is traditionally strong in mid and far infrared spectroscopy, which is an excellent tool to study the mineralogy of dust in different stages of its evolution, as well as trace the underlying physical processes of the environments they are found in: AGB stars, protoplanetary and debris disks.
Fig. 1: The life cycle of interstellar dust. credit: Bill Saxton, NRAO/AUI/NSF
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