Galactic dust

• Our galaxy contains ~10^7 M_sun of dust.

• Its composition can be investigated by looking for absorption features in distant stars which aren't seen in nearby stars:
  • a feature at ~200 nm may be due to C_8 H_8 N_2, or it might be just graphite (soot!).
  • 3.08 micron absorption features are due to ice particles.
  • 9.7 micron absorption features are due to silicates.

• The dust grains reprocess this absorbed radiation, and emit it in the far infrared.

• Thermal mission from this cool dust is clearly visible in the longer wavelength maps created by the DIRBE instrument on COBE:

  

  (original from the COBE Homepage)

  • The dust is mostly found concentrated in a very thin layer (~100 pc thick) in the galactic plane, although thin clouds of dust termed "cirrus" can also be found well away from the plane of the Galaxy.

  • (The second strong feature in the 100 micron map [at the top] is also due to dust emission, in this case from the warmer dust in the plane of the solar system. This emission is known as "zodiacal light").