X-factor (astrophysics)

Origin

Calibration

• The mass of an individual molecular cloud can be inferred from its velocity dispersion. Assuming that the cloud is self gravitating and virialized, and that nearly all of the gas mass is molecular hydrogen, one obtains an estimate of the cloud's H₂ mass.
• H₂ mass can be estimated through gamma ray observations, where gamma ray emission arises from the interaction of cosmic rays with H₂ molecules.
• Using optical and infrared observations, one can estimate the amount of dust in a region and convert to H₂ mass through an dust-to-gas ratio.