Core degenerate scenario

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The core-degenerate scenario is an alternative model for the explosion of a thermonuclear supernova of type Ia .

Type Ia supernovae are the standard candles for cosmic distances and, through the Phillips relationship, led to the discovery of the accelerated expansion of the universe . These supernovae are the sudden onset of thermonuclear reactions in the cores of white dwarfs after crossing the Chandrasekhar limit , in which carbon is burned and the compact star is completely destroyed. The standard models for the thermonuclear supernovae are the single and the doubly degenerate scenario. In the simply degenerate scenario, a white dwarf in a binary star system accretes matter from a companion after crossing the Roche limit and the white dwarf thus overcomes the Chandrasekhar limit mass. In the twofold degenerate scenario, two white dwarfs collide in a binary star system after the radiation of gravitational waves and merge into a supermassive white dwarf, which explodes as a type Ia supernova.

Both theoretical models are not confirmed by observations. In the case of the simply degenerate scenario, the mass donor companion should absorb large amounts of energy through the supernova explosion and not be in thermal equilibrium for a few thousand years after the supernova. The search for such former companion stars in and near supernova remnants has so far been unsuccessful. In the case of the doubly degenerate scenario, there should be a strong increase in X-rays before the explosion, as the lower-mass white dwarf is torn apart by tidal forces and forms a ring around the more massive white dwarf. By accretion from the ring to the white dwarf, a subspecies of the super-soft X-ray sources should form. Neither could X-rays be detected from the location of a type Ia supernova before the outbreak, nor is the number of Super Soft X-ray Sources sufficient to explain the observed frequency of this subspecies of supernovae.

The core degenerate scenario also describes the lack of interaction with circumstellar matter in supernovae such as SN 2011fe, which is expected in both the single and the double degenerate scenario. The core-degenerate scenario arises in a binary star system consisting of a white dwarf and a star that has left the main sequence and is already on the asymptotic giant branch . The red giant continues to expand until the white dwarf orbits the common center of gravity within the giant star's atmosphere . Due to the internal friction, the white dwarf is braked and reduces the distance to the core of the red giant until the two merge. This can create a white dwarf whose mass is above the Chandrasekhar limit and rotates extremely quickly. The rotation stabilizes the white dwarf against gravitational collapse . The former atmosphere of the red giant is thrown off during the common envelope phase in the form of a luminous red nova .

The rapidly rotating white dwarf loses its torque only slowly through an interaction between a stellar wind and the magnetic field of the compact star. As a result, delays between the Common Envelop phase and the explosion as a supernova of up to 10 billion years can occur if the rotational speed has been slowed down to such an extent that the gravitational collapse is no longer averted. The core-degenerate scenario produces white dwarf supernovae with masses between 1.4 and 1.48 solar masses , which supports the observed homogeneity of this type of supernova. However, according to rough estimates, the core-degenerate scenario can only be responsible for about 10 percent of the observed supernovarates and cannot explain either the Super Chandrasekhar supernovae or the Iax-type supernovae .

literature

  • Noam Soker, Enrique Garcia-Berro, Leandro G. Althaus: The explosion of supernova 2011fe in the frame of the core-degenerate scenario . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1309.0368v1 (English).
  • Marjan Ilkov, Noam Soker: The number of progenitors in the core - degenerate scenario for type Ia supernovae . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1208.0953v3 (English).
  • Noam Soker: The core-degenerate scenario for type Ia supernovae . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1109.4652v1 (English).
  • Marjan Ilkov, Noam Soker: Type IA supernovae from very long delayed explosion of core - WD merger . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1106.2027v3 (English).