Interstellar Medium and Molecular Clouds

Flashcards covering key concepts from the lecture on detecting the interstellar medium, including interstellar reddening, dust emission, 21-cm radiation, molecular hydrogen, tracers, and molecular clouds.

Interstellar Reddening

The phenomenon where visible light, especially blue light, is absorbed and scattered more by small dust particles in nebulae, causing the transmitted light to appear not only dimmed but also redder.

Dust Emission

The process where cosmic dust re-radiates energy it absorbs, but at infrared wavelengths, causing optically dark nebulae to appear bright in infrared images.

21-cm Radiation

A long-wavelength radio emission (21 cm) produced when an electron in an atomic hydrogen atom flips its spin from a slightly higher energy state to a lower one. It is important because it is not obscured by dust, allowing detection of atomic hydrogen clouds over long distances.

Molecular Hydrogen (H2)

The form in which most hydrogen exists in the coldest regions of space (~10 K), which does not emit 21-cm radiation.

Tracers

Other molecules, significantly less abundant than hydrogen, which emit their own radiation and are therefore easier to detect, used to map out the locations of molecular hydrogen.

Molecular Clouds

Dense regions of space (approximately 1000 atoms/cm³) primarily composed of molecular hydrogen, containing 100,000 to a few million solar masses of material, and are sites of future star formation.