Astrophysics (Index)About

virial parameter

(calculated quantity showing whether a cloud is gravitationally bound)

The virial parameter is a quantity calculable from the mass, radius and velocity dispersion of a system such as a molecular cloud or dense core, that demonstrates whether it is gravitationally bound. It is essentially the ratio of the cloud's kinetic energy to gravitational potential energy.

     5σ²R
 α = ————
      GM

If α >> 1, the system is not gravitationally bound, and must be held together by external pressure. If gravitationally bound, α ~ 1. This relation is commonly used to deduce the mass of molecular clouds.


(physics,clouds,measure,limit)
Further reading:
http://dictionary.obspm.fr/index.php/index.php?showAll=1&formSearchTextfield=virial+parameter
http://www.eso.org/~tstanke/thesis/chap6_4.html
https://ui.adsabs.harvard.edu/abs/2013ApJ...779..185K/abstract
https://ui.adsabs.harvard.edu/abs/1992ApJ...395..140B/abstract

Index