Cosmic dust

The interstellar dust is part of the interstellar medium which does not also consists of neutral / ionized gas molecules, radiation and magnetic fields. Depending on the origin, a distinction is even interplanetary, planetary and galactic dust next to interstellar dust. The interstellar dust makes mainly by absorbance noticeable, especially within the galactic disc of the Milky Way. Furthermore, dust is directly detectable by its infrared emission.

The dust particles have a mean diameter of about 0.3 microns, but large deviations. The exact distribution of the diameter of the dust particles is still unknown. The dynamics of growth ( by addition of additional material ) and destruction ( by supernova shock waves ) of the dust particles is also still largely unknown. It is, however, now accepted that stardust makes only a very small contribution to the interstellar dust, which means that this mainly occurs directly in the interstellar medium.

The chemical composition is determined by determining the elemental abundances in the interstellar gas and compared with the element abundances in the sun. Are certain elements depleted in the gas, so they are most likely condensed in the dust. As the main constituents of interstellar dust are:

  • Silicates, particularly pyroxenes ( MgxFe1 - xSiO3 ) and olivine ( Mg2xFe2 ( 1-x) SiO4).
  • Carbon in the form of graphite, but not in the typical plane-parallel stratification, rather than ball. Any carbon is also in the form of fullerenes.
  • Ice, mainly water ice and CO2 ice.

Furthermore, it is now believed that interstellar dust particles deviate significantly from the idealized spherical shape. In addition they will likely contain up to 40% (volume) of vacuum pockets.

Typical dust temperatures range from 50 to 100 degrees Kelvin. Clouds of dust and cold molecular clouds ( temperatures about 10 to 20 Kelvin ) are the main regions of star formation. Furthermore, there are reflection nebulae, these are dust clouds that reflect the light of nearby stars.

References

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