An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The phenomenon wherein the → quarks within a → hadron get closer together, the force of containment gets weaker so that it asymptotically approaches zero for close confinement. According to → quantum chromodynamics, the quarks in close confinement are completely free to move about. On the contrary, the further we try to force the quarks apart, the greater the force of containment. The 2004 Nobel Prize in Physics was awarded to David Gross, Frank Wilczek, and David Politzer for their discovery of asymptotic freedom. This discovery established quantum chromodynamics as the correct theory of the → strong interaction.

→ asymptotic; → freedom.

A transition in which a bound electron is liberated. → free-bound emission; → free-free emission.

Bound, p.p. of → bind; → free.

Of a → mechanical system, the number of → independent variables needed to describe its configuration.

→ degree; → freedom.

The condition in a plasma when the → Lorentz force is zero, that is when the electric current flows along the magnetic field. Force-free magnetic fields are encountered in astrophysical plasmas with negligible gas pressure. The solar corona is the best available example of such fields in action in a plasma.

→ force; → free; → magnetic; → field.

Not physically bound by something.
→ free atmosphere, → free body, → free charge, → free electron, → free expansion phase, → free fall, → free flow, → free occurrence, → free oscillation, → free radical, → free system, → free-bound emission, → free-fall time, → free-floating object, → free-free emission, → freedom, → bound-free transition, → force-free magnetic field, → Gibbs free energy, → Helmholtz free energy, → mean free path, → universality of free fall.

From M.E. fre, O.E. freo "free, exempt from," also "noble, joyful;" cf. Ger. frei, Du. vrij; ultimately from PIE *prijos "dear, beloved;" cf. Av. frāy- "to satisfy, propitiate," friθa- "beloved; dear," friθô.tara- "more beloved," Mod.Pers. fari "happy, fortunate, blessed; pleasing, good," Skt. priyá- "beloved, wished for;" Gk. praos "mild, gentle."

Âzâd "free," from Mid.Pers. âzât "free, noble;" Av. āzāta- "high-born, noble," from zan- "to bear, give birth to a child, be born," infinitive zazāite, zāta- "born," āsna- "innate, natural;" cf. Skt. janati "begets, bears;" Gk. gignesthai "to become, happen," genes "born;" L. gignere "to beget;" PIE base *gen- "to give birth, beget."

That part of the atmosphere where the effects of the ground on the → turbulence conditions are negligible.

→ free, → atmosphere.

A → rigid body not constrained with other bodies and which from any given position can be displaced in any direction in space. Opposite of → constrained body.

→ free; → body.

An electric charge which is not held by another charge, in contrast to a → bound charge.

→ free; → charge.

An electron that is not attached to an → atom, → molecule, or → ion and is free to move under the influence of a present electric or magnetic field.

→ free; → electron.

The first phase of → supernova remnant (SNR) evolution in which the surrounding → interstellar medium (ISM) has no influence on the expansion of the → shock wave, and the pressure of the interstellar gas is negligible. The shock wave created by the → supernova explosion moves outward into the interstellar gas at highly → supersonic speed. Assuming that most of the → supernova energy  E_SN is transformed into → kinetic energy of the ejected gas, the ejection velocity v_e can be estimated from E_SN by using E_SN = (1/2) M_ev_e², which leads to v_e = (2E_SN / M_e)^(1/2), where M_e is the ejected mass. The schematic structure of the SNR at this phase can be described as follows: behind the strong → shock front which moves outward into the ISM, compressed interstellar gas accumulates forming a → shell of interstellar gas. This shell of swept-up material in front of shock does not represent a significant increase in the mass of the system. After some time the accumulated mass equals the ejected mass of stellar material, and it will start to affect the expansion of the SNR. By definition, this is the end of the free expansion phase, and the corresponding radius of the SNR, called → sweep-up radius, R_SW, is defined by M_e = (4π/3) R_SW³ρ₀, that is R_SW = (3M_e / 4πρ₀)^(1/3), where ρ₀ is the initial density of the ISM. This radius is reached at the sweep-up time t_SW = R_SW/v_e. The free expansion phase lasts some 100-200 years until the mass of the material swept up by the shock wave exceeds the mass of the ejected material. Then the following → snowplow phase starts.

→ free; → expansion; → phase.

The motion of a body under the influence of → gravity alone. See also → free-fall time.

→ free; → fall.

A fluid flow which develops when density differences within the fluid are the only driving forces. See also → forced flow.

→ free; → flow.

An → occurrence of a → variable in a → wff, → iff it is not a → bound occurrence.

→ bound; → occurrence.

Oscillation of any system in stable equilibrium under the influence of internal forces only, or of a constant force originating outside the system, or of both.

→ free; → oscillation.

A chemical radical that can exist independently from atoms or group of atoms.

→ free; → radical.

A → mechanical system if all of its constituent particles or bodies can occupy arbitrary points in space or have arbitrary velocities. Otherwise, it is called a → constrained system.

→ free; → system.

The radiation emitted when a → free electron is captured by an → ion. See also: → free-free emission; → bound-free transition.

→ free; → bound; → emission.

The characteristic time it would take a body to collapse under its own → gravitational attraction, if no other forces existed to oppose the collapse. It is given by: t_ff = (3π/32 ρ₀ G)^1/2, where ρ₀ denotes the initial density and G the → gravitational constant. Free-fall time is independent of the starting radius. Also known as → dynamical time scale.

→ free fall; → time.

A population of → substellar objects which are not bound to stars; they are detected in young star clusters. Their masses, estimated from their fluxes, is several Jupiter masses, lower than those of → brown dwarfs. Their formation is not yet explained. Among the envisaged possibilities: 1) These objects form like stars, from protostellar core collapse and subsequent accretion; 2) they form as low-mass members of small groups, and are ejected from the group; 3) they form like planets within circumstellar disks of higher-mass objects, but are ejected either due to internal dynamics or external interactions.

→ free; floating, from M.E. float, from O.E. flotian "to float" (cf. O.N. flota, M.Du. vloten); → object.

Barâxt, → object; šenâvar "that swims, floats," from šenâ "swimming;" Mid.Pers. šnâz "swim," šnâzidan "to swim;" Av. snā- "to wash, swim;" cf. Skt. snā- "to bathe, to wash;" L. nare, natare "to swim" (Fr. nage, nager, natation; Sp.nadar, natacion).

→ Electromagnetic radiation produced in a → plasma by → free electrons scattering off → ions without being captured. The electrons are free before the interaction and remain free afterward.

→ free; → emission.