Epsilon mechanism

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The epsilon mechanism is an astrophysical process that leads to vibrations in stars .

The mechanism is caused by the fact that the energy release ε ( epsilon ) through thermonuclear reactions in the core of a star (or in a shell around it ) depends on the pressure and on the temperature (as well as on the chemical composition).

Suspected occurrence

Pulsations due to the epsilon mechanism are assumed for:

Basics

In general there is a hydrostatic equilibrium in a star between the gravitation , which tries to contract the star, and the gas pressure and the radiation pressure , which is created by the nuclear fusion inside. Deviations from this equilibrium can cause the star to pulsate.

description

The epsilon mechanism works as follows:

  • The material in that zone of the star in which nuclear fusion takes place heats up or increases its density .
  • This increases the rate of nuclear fusion , which further increases pressure and temperature.
  • The radius of the star no longer corresponds to the new state of equilibrium: the pressure exceeds the forces that act on the layer of the star through gravity, and expansion occurs.
  • Due to the inertia , the zone expands beyond the equilibrium point .
  • Due to the expansion, there is a cooling of the zone and a decrease in density.
  • The gravitational forces exceed the pressure, the star compresses, again beyond the desired equilibrium.
  • After the equilibrium of forces has been exceeded, the density and temperature in the nuclear fusion zone rise again and the cycle starts all over again. An oscillation is created , the star pulsates.

In principle, the epsilon mechanism works like a compression-ignition diesel engine .

No evidence so far

In contrast to the kappa mechanism , in which a star pulsates due to temperature-dependent changes in opacity , the epsilon mechanism has not yet been proven beyond doubt. This is because the energy is generated deep inside the star and the oscillations caused by the epsilon mechanism are dampened by the layers above .

Individual evidence

  1. ↑ Rudolph Kippenhahn, A. Weigert: Stellar Structure and Evolution (Astronomy and Astrophysics Library) . Springer Verlag, Berlin 1994, ISBN 978-0-387-58013-5 .
  2. ↑ Marcelo M. Miller Bertolami, Alejandro H. Córsico, Xianfei Zhang, Leandro G. Althaus, C. Simon Jeffery: Pulsations driven by the epsilon mechanism in post-merger remnants: first results . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1210.0262 .
  3. ↑ Ehsan Moravveji, Andres Moya, and Edward F. Guinan: ASTEROSEISMOLOGY OF THE NEARBY SN-II PROGENITOR RIGEL PART II. EPSILON - MECHANISM TRIGGERING GRAVITY-MODE PULSATIONS? In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1202.1836 .
  4. ↑ C. Rodríguez-López, J. MacDonald, A. Moya: Pulsations in M ​​dwarf stars . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1108.1126 .
  5. ↑ Joyce A. Guzik and Catherine C. Lovekin: Pulsations and Hydrodynamics of Luminous Blue Variable Stars . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1402.0257 .
  6. ↑ H. Scheffler, H. Elsässer: Physics of the sun and the stars . Bibliographisches Institut, Mannheim 1990, ISBN 3-411-14172-7 .