virial viriyâl Fr.: viriel Of or pertaining to the interactive forces between components of a system, such as
particles or molecules in a gas or stars in a cluster. From L. vires, plural of vis "strength," and by extension "force" or "energy," first used by Rudolf Clausius in the investigation of problems in molecular physics. Viriyâl, loan from E., as above. |
virial equation of state hamugeš-e hâlat-e viriyal Fr.: équation d'état du viriel In thermodynamics, a generalized → equation of state obtained when the → compression factor Z is expanded in terms of a power series, e.g.: Z = 1 + B(T) / V_{m} + C(T) / V_{m}^{2} + ... → virial; → equation of state. |
virial equilibrium tarâzmandi-ye viriyâl Fr.: équilibre du viriel The condition of a physical system which obeys the → virial theorem. → virial; → equilibrium. |
virial mass jerm-e viriyâl Fr.: masse du viriel The mass of a cluster of stars or galaxies in statistical equilibrium derived by using the → virial theorem. |
virial parameter pârâmun-e viriyâl Fr.: paramètre du viriel A dimensionless parameter that measures the ratio of thermal plus kinetic energies to gravitational energy of a physical system, such as a molecular cloud. The virial parameter is expressed as: α_{vir} = 5σ^{2}R / GM, where R and M are the radius and mass of the cloud respectively, σ is the one-dimensional → velocity dispersion inside the cloud, and G the → gravitational constant. It indicates whether a cloud could be bound or not. For molecular clouds that are confined by their surface pressure and for which self-gravity is unimportant, α_{vir} is much larger than unity, whereas α_{vir} is ~ 1 when the gravitational energy of a clump becomes comparable to its kinetic energy. See, e.g., Bertoldi & McKee, 1992 (ApJ 395, 140). See also → virial theorem. |
virial radius šo'â'-e viriyâl Fr.: rayon du viriel The radius centered on a galaxy containing matter at 200 times the → critical density of the Universe. |
virial temperature damâ-ye viriyâl Fr.: température du viriel The mean temperature at which a gravitationally → bound system would satisfy the → virial theorem. For a system of mass M and radius R with constant density, the gravitational energy per unit mass is W = GM/R. The kinetic energy per unit mass is E = (3/2)kT_{vir}/μ, where k is → Boltzmann's constant and μ the mean molecular weight. According to the virial theorem, E = W/2, which leads to the virial temperature T_{vir} = (1/3)(GM/kR). → virial; → temperature. |
virial theorem farbin-e viriyâl Fr.: théorème du viriel A general equation applicable to a gravitationally → bound system of equal mass objects (stars, galaxies, etc.), which is stable against → dynamical disruption. It states that in such a system the average → gravitational potential energy (W_{vir}) is twice the average → kinetic energy (K_{vir}) of the system: W_{vir} = -2K_{vir}. This general proposition, first derived by Rudolf Clausius (1822-1888), has important applications in a variety of fields ranging from statistical mechanics to astrophysics. See also → virialization, → virial equilibrium, → virialized. |
virialization viriayleš Fr.: virialisation The process whereby a system of gravitationally interacting particles attains stability. The comparable mass components interact with each other, but the whole system does not expand or collapse. Virialization occurs when the → potential energy is twice the negative → kinetic energy: - W_{vir} = 2 K_{vir} (→ virial theorem). In the case of a → galaxy cluster, when the cluster is virialized the merging process and the collapse of matter have finished and the formation process of the galaxy cluster is considered to be done. A cluster has formed by → hierarchical clustering. Virialized clusters, in other words finished clusters, can be found by looking at their radius and density. A cluster is virialized when it satisfies the condition: R_{vir} ~ R_{max}/2, where R_{vir} is the radius when the cluster is virialized and R_{max} is the radius when the collapse starts. From this condition it follows that the object is 8 times denser at virialization than when the collapse started. Verbal noun of → virialize. |
virialize viriyâlidan Fr.: virialiser To undergo → virialization. |
virialized viriyâlidé Fr.: virialisé That has undergone → virialization. Past participle of → virialize. |