angular momentum problem پراسهی ِ جنباک ِ زاویهای parâse-ye jonbâk-e zâviye-yi Fr.: problème de moment angulaire The fact that the Sun, which contains 99.9% of the mass of the
→ solar system, accounts for about 2% of the total
→ angular momentum of the solar system. The problem of outward
→ angular momentum transfer has been a main topic of interest for
models attempting to explain the origin of the solar system.
More generally, in star formation studies, the question of the origin of the angular momentum
of a star and the evolution of its distribution during the early
history of a star. Consider a filamentary molecular cloud with a length of 10 pc and a
radius of 0.2 pc, rotating about its long axis with a typical
→ angular velocity of Ω = 10-15 s-1.
At a matter density of 20 cm-3,
the cloud is about 1 → solar mass.
The cloud collapses to form a star with
radius of 6 x 1010 cm. The conservation of angular momentum
(∝ ΩR2) requires that as the radius decreases from 0.2 pc to
the stellar value, a factor of 107, the value of Ω must increase by 14
orders of magnitude to 10-1 s-1. The star’s
rotational velocity will be 20% the speed of light and the ratio of
→ centrifugal force to gravity at the equator will be about
104. Observational data, however, indicate that the youngest
stars are in fact rotating quite slowly, with rotational velocities of
10% of the → break-up velocity. The angular momentum problem
was first studied in the context of single stars forming in isolation (L. Mestel,
1965, Quart. J. R. Astron. Soc. 6, 161). For more information see,
e.g., P. Bodenheimer, 1995, ARAA 33, 199; H. Zinnecker, 2004, RevMexAA 22, 77;
R. B. Larson, 2010, Rep. Prog. Phys. 73, 014901, and references therein.
See also: → angular; → momentum;
→ problem. |
