- #36
Garth
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wabbit said:
Agreed
wabbit said:In any case, as I understand it if different channels estimated separately then yield the same distance/redshift curve this would corroborate the existing (LCDM) model, while different curves for different channels would require some explanation.
And my point was that the naivete appears only when we expect an overly broad class of objects to be standard candles, when in fact it is only the appropriate subgroups that are standard candles. The trick is to have enough observed features to tell which standard candle they are. I'm interpreting the new information as saying you cannot any more just go with the light curve in one passband, or maybe even the light curve in all available passbands, you need more complete spectral information. So the question for now is, if we throw out all the observations that are not sufficiently constrained to be used as standard candles, do enough datapoints remain to still see evidence for acceleration, and is the acceleration still consistent with a cosmological constant equation of state? Or is it impossible to cull the subgroups, and all we can do is estimate and correct for their relative populations hidden in the data, and then can we still conclude the results are consistent with a cosmological constant? That would seem to be possible to address with current data, because if the answer is "we don't yet have a dataset like that, we need new observations that can constrain these subgroups", then it would seem the recent claims of "precision cosmology", and the Nobel prize associated with it, are all premature.Garth said:My point has always been that the simple assumption that Type 1a SNe are standard candles over cosmological time scales (z=1 and beyond) is naive.
What is especially disturbing is that even armed with the knowledge that there are different species of Type 1a SNe that produce different absolute magnitudes, nobody seems to care. There are currently 6,513 supernovae listed in Harvard's database, and the Type 1a SNe discovered after 2007 were identified using SNID software developed by Stéphane Blondin and John L. Tonry, which used the correlation techniques published in 1979. So the software will not be able to distinguish between a sub-Chandrasekhar, a Chandrasekhar, and a super-Chandrasekhar Type 1a SNe, yet it continues to be used.Garth said:Yes, as we have yet to do that analysis of the SNe 1a spectral classes and compare them with the gold data set, then the present assumption that they are standard candles, and hence the deduction about the amount of DE, is naive.
The situation hasn't changed since 1998 when DE, and the [itex]\Lambda[/itex]CDM model, based on them being standard candles was introduced, although a lot more information has come to light
Garth
It is certainly not negligence in any of the published studies before the different types of Type 1a SNe were known. They were written with the best information available at the time. However, that changed after 2006.wabbit said:@|Glitch| - This seems quite serious, if I understand correctly what you are saying, this would seem to imply at best serious negligence in a lot of published studies. Am I misunderstanding you ?
To clarify, could you confirm whether and how you see the issue you refer to applying for instance in following :
The Hubble Space Telescope Cluster Supernova Survey: V. Improving the Dark Energy Constraints Above z>1 and Building an Early-Type-Hosted Supernova Sample, Suzuki & al.
- or in other specific cases ?
Thanks
The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star.
The accelerating expansion of the Universe, and the need for dark energy, were inferred from observations of type Ia supernovae. There is a consensus that type Ia supernovae are thermonuclear explosions that destroy carbon-oxygen white dwarf stars that have accreted matter from a companion star, although the nature of this companion remains uncertain. These supernovae are thought to be reliable distance indicators because they have a standard amount of fuel and a uniform trigger: they are predicted to explode when the mass of the white dwarf nears the Chandrasekhar mass of 1.4 solar masses (M(o)). Here we show that the high-redshift supernova SNLS-03D3bb has an exceptionally high luminosity and low kinetic energy that both imply a super-Chandrasekhar-mass progenitor. Super-Chandrasekhar-mass supernovae should occur preferentially in a young stellar population, so this may provide an explanation for the observed trend that overluminous type Ia supernovae occur only in 'young' environments. As this supernova does not obey the relations that allow type Ia supernovae to be calibrated as standard candles, and as no counterparts have been found at low redshift, future cosmology studies will have to consider possible contamination from such events.
At z > ~0.9, any SN bright enough to be detected is overwhelmingly likely to be Type Ia due to the faintness of core-collapse SNe relative to SNe Ia (e.g., Dahlen et al. 2004; Li et al. 2011; Meyers et al. 2011). Furthermore, while “probable” candidates are not as certain as “secure” candidates, this is still a fairly high-confidence type determination: A “probable” SN Ia means that a SN Ia light curve template has a χ2 P-value that is 103 times larger than any SN CC value.
The data they are collecting I am sure is "solid." I have no reason to doubt any of the data being presented. The problem is that they are not collecting enough data to be able to distinguish between sub-Chandrasekhar, Chandrasekhar, and super-Chandrasekhar Type 1a SNe. Until that changes, there is no such thing as a "standard candle" in cosmology.Chronos said:The original supernova data still look solid to me. There is no evidence of faults in the data, or error bars. Science is constrained by data, not fairies. While that does not eliminate the possibility of error, it does limit the parameter space.
The paper I am referring to is from 2011.|Glitch| said:It is certainly not negligence in any of the published studies before the different types of Type 1a SNe were known. They were written with the best information available at the time. However, that changed after 2006.
So either these distinctions are inconsequential for the specific results this study obtains, or you are in fact saying that this 2011 paper ignores well known and relevant results and uses wrong assumptions.The paper in which you refer merely assumes that all SNe z > ~0.9 are Type 1a. An erroneous assumption at that. They should have known that they could be including super-Chandrasekhar Type 1a SNe in their data and taken measures to ensure that was not the case.
The 2011 paper was before the new classification of Type 1ax was created in 2013, so they had no reason to determine the blue-shift of the ejecta because they could not have known at the time there was a distinction. Hence, the data is incomplete which had absolutely nothing to do with negligence. However, they should have been aware that Type 1a SNe at z > ~1 may include super-Chandrasekhar Type 1a SNe and take steps to ensure those SNe did not contaminate their data, since the paper that identified the problem was published 5 years earlier.wabbit said:The paper I am referring to is from 2011.
So either these distinctions are inconsequential for the specific results this study obtains, or you are in fact saying that this 2011 paper ignores well known and relevant results and uses wrong assumptions.
I do not have the expertise to evaluate your claims, but given their very strong nature I would think they should require strong evidence as well. I was unaware there was such doubt about the results of this and other collaborations.
Edit: to clarify - as I understand it, the existence of several types of supernova within the initial broad standard candle class is not in question, and is discussed in several of these studies. The issue is whether they disregarded known and relevant distinctions. Your last post appears to make the much less controversial claim that some distinctions could not be corrected with the existing data (up to now, not just from 2006) despite all best efforts to do so. This is very different and not what I refer to as your strong claims.