SN1a under fire as standard candles

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Discussion Overview

The discussion centers on the role of Type Ia supernovae (SN1a) as standard candles in cosmology, particularly in light of a paper proposing an alternative model for their progenitors. Participants explore the implications of this model, the challenges in measuring distances using SN1a, and the potential variability in their properties based on different formation channels.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants reference a paper discussing alternative models for SN1a progenitors and their observational predictions, suggesting that validation could have significant consequences for cosmology.
  • There is speculation about the detectability of quark novae as a new category of SN1a and their potential impact on distance measurements.
  • Participants note the difficulty of cross-checking distances for SN1a beyond 100 Mpc, while acknowledging that methods like the D–σ relation and Tully-Fisher relation exist, albeit with error margins.
  • One participant expresses skepticism about the ability to improve absolute brightness estimates of SN1a from their spectra, despite the potential for more accurate distance measurements.
  • Discussion includes the idea that if SN1a arise from different channels (single-degenerate, double-degenerate, and quark nova), there could be systematic variations in observed magnitudes over cosmological distances.
  • Some participants highlight the implications of non-standardizable SN1a and the expected evolution of the relative production rates of different channels over time.
  • Concerns are raised about the compatibility of unusual detonation paths with observational data, questioning the rarity of such supernovae.

Areas of Agreement / Disagreement

Participants express a range of views on the implications of the alternative model for SN1a progenitors, with no consensus reached on the impact of these findings on their reliability as standard candles. There is acknowledgment of the challenges in measuring distances and the potential for variability in SN1a properties, indicating ongoing debate.

Contextual Notes

Limitations include the uncertainty surrounding the error margins of various distance measurement methods and the dependence on the definitions of the different channels of SN1a formation.

Chronos
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This paper, http://arxiv.org/abs/1402.2717, discusses an alternative model for SN1a progenitors and offers observational predictions to test it based on SN2014J. If the model is validated it would have far reaching consequences for cosmology.
 
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Interesting paper, it would be interesting to see if a quark nova 1A is detectable according to this paper. Or if they are shown to exist.

Sounds to me though that this applies to certain white dwarfs going supernova, a new category so to speak.

Although if found to be true I don't think it will greatly influence too much on the distance ladder. Other than an increase in accuracy. May influence regions that we have no reliable cross check such as stellar parallax. I state this observation based on knowing that no one method of distance measure is truly relied upon as being an absolute. As far as I understand it every standard candle is cross checked with other means of determining distance. Provided a means of cross check is possible.
 
One of the problems with SN1a is their distance is very difficult to cross check beyond 100 Mpc [about z=.023].
 
Difficult yes, however there are methods for that range, although they also have a degree of error. I've read numerous references to the D–σ relation, SBF (surface brightness fluctuations)
and the Tully Fisher relation as being cross checks at those ranges. Mostly when I was studying the cosmic distance ladder. I couldn't tell you their margin of error lol. I only half remember what I self studied. Been a few months, if I recall though the D–σ relation is used at 100 MPC. Could be wrong, I can't recall any cross checks beyond 100 MPC though. However my memory is fuzzy on the subject

edit: by the way if anyone has good articles covering the methods above and other methods used in the cosmic distance scale, preferably with the technical details I would be interested. The papers I have only cover select ones.
 
Last edited:
Chronos said:
This paper, http://arxiv.org/abs/1402.2717, discusses an alternative model for SN1a progenitors and offers observational predictions to test it based on SN2014J. If the model is validated it would have far reaching consequences for cosmology.
Meh, I'm not too worried about SN1a's usefulness as standard candles. Their variance is cross-checked through observations, and the fact that SN1a measurements of expansion coincide with other measurements of expansion shows that they can't have a bias with redshift that is dramatic enough to really put the results into question.

However, if we gain a greater understanding of SN1a events, we may be able to better estimate their absolute brightness from their spectrum, resulting in more accurate estimates of expansion from the same data. I'm skeptical that this will be possible, but we'll see.
 
If there are three channels for the detonation of a White Dwarf; "the single-degenerate (SD) channel is the accretion onto the WD from a nondegenerate companion (Whelan & Iben 1973) and the double-degenerate (DD) channel provides the mass from the merger of two WDs (Iben & Tutukov 1994; Webbink 1984)." together with "the explosion of a companion neutron star (NS) as a Quark-Nova Ia (QN-Ia).", and the SN Ia step of distance ladder is an average of the combination of these three, then there could well be a systematic variation over cosmological distances in the observed magnitude, caused by a secular evolution and change in the relative number of these three species.

Garth
 
I found this intriguing "...Interestingly SNe-Ia formed through this channel are not standardizable using usual methods (Ouyed et al. 2013a) leading to profound implications for cosmology if the majority are formed in this way." It appears, even assuming this path to detonation is unusual, it could really muck things up.
 
Yes, and as the universe evolves it is to be expected that the relative number of SN Ia's produced by each channel would vary as it takes time for a star to become degenerate.

Therefore, for example, I would expect that the ratio between the single (SD) and double degenerate (DD) channel would decrease with cosmological time. (i.e. there would be relatively fewer DD's at an earlier epoch.)

Garth
 
Chronos said:
I found this intriguing "...Interestingly SNe-Ia formed through this channel are not standardizable using usual methods (Ouyed et al. 2013a) leading to profound implications for cosmology if the majority are formed in this way." It appears, even assuming this path to detonation is unusual, it could really muck things up.
Unless such supernovae are extremely rare, it's hard to see how that statement can match observations.
 

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