An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 3 Search : di-
Bondi-Hoyle accretion
  فربال ِ بوندی-هویل   
farbâl-e Bondi-Hoyle

Fr.: accrétion de Bondi-Hoyle   

The → accretion of mass by a star (assumed as point particle) moving at a steady speed through an infinite, uniform gas cloud. It is directly proportional to the star mass (M) and the medium density (ρ) and inversely proportional to the relative star/gas velocity (v). In its classical expression: 4πρ(G M)2 / v3, where G is the → gravitational constant. See Bondi & Hoyle (1944, MNRAS 104, 273) and Bondi (1952, MNRAS 112, 195). For a recent treatment of accretion in a turbulent medium see Krumholtz et al. 2006 (ApJ 638, 369).

Named after Hermann Bondi (1919-2005), an Anglo-Austrian mathematician and cosmologist and Fred Hoyle (1915-2001), British mathematician and astronomer best known as the foremost proponent and defender of the steady-state theory of the universe; → accretion.

Bondi-Hoyle accretion radius
  شعاع ِ فربال ِ بوندی-هویل   
šo'â'-e farbâl-e Bondi-Hoyle

Fr.: rayon de l'accrétion de Bondi-Hoyle   

In the → Bondi-Hoyle accretion process, the radius where the gravitational energy owing to star is larger than the kinetic energy and, therefore, at which material is bound to star. The Bondi-Hoyle accretion radius is given by RBH = 2 GM / (v2 + cs2) where G is the gravitational constant, M is the stellar mass, v the gas/star relative velocity, and cs is the sound speed.

Bondi-Hoyle accretion; → radius.

di-
  دو-، دی-   
do-, di-

Fr.: di-   

A prefix meaning "two; twice; double." → dimer, → diode, → dipole, → diproton.

L. di, from Gk., → two.