Interstellar medium and astrochemistry

6 problems

• What produces the anomalous microwave emission from dust?

  Contested

  Our Galaxy emits extra microwaves that follow the distribution of dust but are not explained by its warmth. Tiny spinning dust grains could produce it, but which grains is not known.

• What carrier produces the 2175 Angstrom extinction bump?

  Open

  Interstellar dust absorbs ultraviolet light most strongly near a wavelength of 2175 Angstrom. The bump's position barely changes from place to place while its width does, and no material reproduces both facts.

• How do complex organics and aromatic molecules form in cold clouds?

  Open

  Radio telescopes have found large ring-shaped carbon molecules and other complex organics in a dark cloud only about 10 degrees above absolute zero. Chemistry models predict far smaller amounts than are seen.

• Why is the cosmic-ray ionization rate in diffuse clouds so high?

  Open

  Molecules such as H3+ show that diffuse interstellar clouds are ionized about ten times faster than the cosmic rays measured near the Sun can explain. Either unseen low-energy cosmic rays exist or the chemistry is misunderstood.

• Which molecules cause the diffuse interstellar bands?

  Open

  Starlight crossing interstellar gas shows hundreds of absorption bands, called diffuse interstellar bands, whose source is unknown. After a century, only one molecule, the positively charged buckyball C60+, has been confirmed.

• How did galaxies accumulate so much dust within one billion years?

  Open

  Some galaxies seen less than a billion years after the Big Bang already contain tens of millions of Suns' worth of dust. Supernovae alone seem unable to make that much in the time available.