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Type Ia Supernova are generally thought to be white dwarfs that, either by accretion of mass from a companion (single degenerate), or as a result of a merger with a white dwarf companion (double degenerate), approach and then exceed 99% of the Chandrasekhar limit of about 1.44 M☉, at which point the star begins a unstable process of carbon fusion that leads to complete deflagration and detonation of the star in a supernova.
Because the detonation mass is more or less fixed the SNe are all about the same luminosity and they can be used as standard candles. They do vary a little and the Phillips relationship has been derived by observation, which relates the peak luminosity to the speed of luminosity evolution after maximum light.
The characteristics of the Type 1a is that its spectrum is rich in carbon and oxygen and deficient in hydrogen. It is for this reason that they are thought to be the detonation of a carbon star, a white dwarf of ~ 1.4 M☉.
They are very bright and are the principal way of observing the effect of Dark Energy, and one pillar of the consensus standard [itex]\Lambda[/itex]CDM model of cosmology.
However an eprint Exploring an Alternative Channel of Evolution Towards SNa Ia Explosion (MNRAS accepted) has recently been published that would suggest they are not all standard candles.
The paper looks at hydrogen and helium contamination of the WD progenitor and finds that a very small amount of hydrogen or a greater amount of helium may cause premature detonation.
From #8 Conclusions:
My confusion is that such variation in SNe Ia luminosity should have already been observed in the "standard candle" calibration of these objects.
How would such a variation affect the 'Gold Standard' dataset of distant SNe Ia and the standard [itex]\Lambda[/itex]CDM model?
Garth
Because the detonation mass is more or less fixed the SNe are all about the same luminosity and they can be used as standard candles. They do vary a little and the Phillips relationship has been derived by observation, which relates the peak luminosity to the speed of luminosity evolution after maximum light.
The characteristics of the Type 1a is that its spectrum is rich in carbon and oxygen and deficient in hydrogen. It is for this reason that they are thought to be the detonation of a carbon star, a white dwarf of ~ 1.4 M☉.
They are very bright and are the principal way of observing the effect of Dark Energy, and one pillar of the consensus standard [itex]\Lambda[/itex]CDM model of cosmology.
However an eprint Exploring an Alternative Channel of Evolution Towards SNa Ia Explosion (MNRAS accepted) has recently been published that would suggest they are not all standard candles.
The paper looks at hydrogen and helium contamination of the WD progenitor and finds that a very small amount of hydrogen or a greater amount of helium may cause premature detonation.
From #8 Conclusions:
(Bold mine)The main results of the present study suggest that:
- The presence of hydrogen even in extremely low concentrations (from 10−16 to 10−21) can raise the pycno-nuclearreaction rates in density intervals from 107 to 108 g cm−3. The same is true for helium at somewhat higher threshold densities.
- In the case of hydrogen, the above density interval corresponds to WD masses from ≃ 0.85 to 1.2M⊙, well below the known limit of the Chandrasekhar mass.
- In WDs in this mass range, the energy released by pycno-nuclear reactions like 1H +12 C may trigger the ignition of CC-burning in a two steps process that we have named the fuse of C-ignition. The age at which this is expected to occur depends on the WD mass and abundance of residual hydrogen. The fuse-induced C-ignition is likely followed by thermal runaway according to the classical mechanisms.
- Even WDs with masses as low as 0.85 M⊙ may experience nuclear runaway.
Our results could in principle radically change not only the current understanding of the structure and evolution of WDs but also imply that single WDs may be progenitors of type Ia SNe.
......
If the results of our exploratory project are confirmed by further investigation, important implications for the currently accepted scenario for type Ia SNe will follow. The binary origin of type Ia SNa explosion would be no longer strictly necessary. Isolated WDs with masses well below the Chandrasekhar limit may reach the threshold for pycno-nuclear burning and consequent SNa explosion due to the survival of traces of light elements. These impurities may remain inactive for long periods of time and be activated only when the WDs reach the liquid-solid regime. Owing to the large range of WD masses that could be affected by the presence of impurities and undergo thermal runaway and consequent SNa explosion, the nature of standard candle so far attributed to type Ia SNe may not be true. Because of the far reaching implications, the whole subject deserves careful future investigation.
My confusion is that such variation in SNe Ia luminosity should have already been observed in the "standard candle" calibration of these objects.
How would such a variation affect the 'Gold Standard' dataset of distant SNe Ia and the standard [itex]\Lambda[/itex]CDM model?
Garth
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