Darwin instability

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The Darwin instability (after George Darwin ) is an unstable state in the distribution of angular momentum in binary systems .

Darwin instability occurs when the angular momentum in the rotation of the stars exceeds a threshold value of a third of the orbital angular momentum from the movement of the stars around their common center of gravity. As a result, the tidal forces can no longer synchronize the rotation of the heavy star with the period of orbit of the binary star system . The orbital speed is now greater than the speed of rotation of the primary star, and as a result, a rapid transfer of angular momentum to the primary star begins. This reacts with a flattening to the higher speed of rotation, which increases the friction of the atmosphere between the two stars. The friction leads to a spiral movement of the smaller star around the primary star until a rapidly rotating single star has emerged from the binary star system.

It is believed that the Darwin instability leads to the formation of blue stragglers from W Ursae Majoris stars . The eruption of the bright red Nova V1309 Sco observed in 2008 could also be the result of a Darwin instability.

literature

  • Lifang Li, Fenghui Zhang: The dynamical stability of W Ursae Majoris-type systems . In: Monthly Notices of the Royal Astronomical Society . tape 369 , no. 4 , July 11, 2006, p. 2001-2004 , doi : 10.1111 / j.1365-2966.2006.10462.x .
  • Frederic A. Rasio: The minimum mass ratio of W Ursae Majoris binaries . In: The Astrophysical Journal . tape 444 , no. 1 , May 1995, pp. L41-L43 , doi : 10.1086 / 187855 .
  • GH Darwin: On Figures of Equilibrium of Rotating Masses of Fluid. In: Royal Society of London Series I Proceedings . tape 42 , January 1887, p. 359-362 , doi : 10.1098 / rspl.1887.0078 .