# Are SNe Ia Standard Candles?

1. Feb 5, 2007

### Garth

R. G. Vishwakarma has replaced his paper Recent Supernovae Ia observations tend to rule out all the cosmologies? with the accepted version. He does not say accepted by whom.
(Emphasis mine)

Does the high-z SNe Ia data record the evolution of Dark Energy, i.e. $\omega$, or the evolution of the SNe Ia?

Garth

Last edited: Feb 5, 2007
2. Feb 7, 2007

### Locrian

Well, how exactly could our understanding of Ia sn be wrong. . . as a function of distance?

3. Feb 7, 2007

### turbo

Arp, the Burbidges, Narlikar and others believe that at least some component of an object's redshift is intrinsic - that is, it is not due to the peculiar motion of the object, nor is it attributable to the Hubble relation. Theirs is one cosmology that may be supported by the SNe Ia data. Here is why:

If galaxies have intrinsic redshifts, the distances to nearby galaxies will be overestimated because all of the redshift is attributed to the Hubble redshift-distance relationship. The redshifts of more distant galaxies will be less contaminated by intrinsic redshift as a percentage of the total, and therefore, their calculated distances (as estimated by the Hubble redshift-distance relationship) will actually be more accurate than the distances of local galaxies. If this is true, the question becomes not "Why are the absolute luminosities of distant SNe Ias fainter than local ones?" but "Why are the absolute luminosities of local SNe Ia brighter than their more distant counterparts?" In the Arp-Burbidge-Narlikar cosmology, the answer is that local galaxies are closer than we think because we have attributed all their redshift to the Hubble relationship and we have failed to recognize that intrinsic redshifts are adding to the cosmological redshift. It may very well be that distant SNe Ia are good standard candles and the over-luminosity of local SNe Ia are a measure of the error in our distances to local galaxies.

The SNe Ia data are not ruling out all cosmologies, but they are supportive of a cosmology that is not very popular or widely-accepted.

4. Feb 7, 2007

### Garth

Simply, because it is assumed that the intrinsic luminosity of the SNe Ia is thought to be well known, and 'on average' does not change over cosmological time or distance.

It is from their apparent magnitude and the luminosity function that their distance is calculated, and that distance compared with their red shift.

This distance-red shift relationship gives a 'handle' on how the universe is expanding and, as the distant SNe Ia are observed to be fainter than previously expected, the universe is consequently thought to be accelerating in its expansion.

This SNe Ia data set is one part of the bedrock of the standard $\Lambda$CDM model.

However if the intrinsic luminosity is not 'on average' constant then that 'bedrock' becomes 'shifting sand'.....

Garth

Last edited: Feb 8, 2007
5. Feb 7, 2007

### matt.o

And at which redshift does a galaxy cease to be local?

6. Feb 7, 2007

### turbo

There is not a border, but a reduction in the contamination of intrinsic redshift that shrinks with increasing distance.

7. Feb 8, 2007

### Garth

Note: I didn't intend this thread to be primarily a discusion about other cosmologies, just the OP question arising from the OP link paper, i.e. Does the present data support the concept that SNe Ia are standard candles or not?

Garth

8. Feb 8, 2007

### SpaceTiger

Staff Emeritus
Garth gave the correct answer. It is very difficult to constrain the properties of supernovae at high redshift, so we often assume that their properties are similar to those at low redshift. However, there are a number of perfectly good reasons (such as evolving chemical content) to think that their properties might change with redshift, so the question of systematics will always hang over the heads of anyone doing cosmological measurements with SNe Ia.

The initial measurements of the accelerating universe were made with SNe Ia and were greeted with much skepticism for this very reason. However, a number of independent cosmological probes have since lent support to the cosmological model suggested by these SNe measurements, so it's likely that the systematics are not sizable at moderate redshifts (z <~ 1).

9. Feb 9, 2007

### Garth

I agree ST, however does Vishwakarma's paper in the OP link seriously challenge this conclusion?

He claims:
The standard model he claims is ruled out at the 96.6% confidence level and
quoting various papers from which "fairly high" is referring to over the 90% confidence level.

His conclusion seems to be that systematic errors in the SNe Ia analysis are important at z > 0.5

There is also the question of a correct model for SNe Ia as questioned in John Middleditch's eprint (Report-no: LAUR 06-5685): Core-collapse, GRBs, Type Ia Supernovae, and Cosmology
(emphasis mine)

Now I am not advocating Middleditch's model in particular, just using it to show that we do not actually know what SNe Ia are for certain, only that they exhibit weak hydrogen lines (therefore Type I - stripped hydrogen envelope progenitors?) and a strong Si II line with other intermediate 'metals': Nickel-56 through Cobalt-56 to Iron-56, (accreting white dwarf detonation?) and the local ones have very similar absolute luminosity profiles suggesting their role as 'standard candles'.

However, they could also be the result of stellar mergers as proposed in the Middleditch paper. In which case their luminosity may be a function of directionality as well.

Other systematics may also be involved, such as chemical evolution with cosmological age as ST mentioned, or possibly a selection effect whereby there may be a delay in detecting the more distant and fainter SN until later on in their light curve when the luminosity has died down somewhat.

As an example of chemical evolution: the radio-active decay of the Nickel–56 is responsible for the brightest part of the SNe Ia luminosity curve, so a Nickel deficiency in early high-z SNe Ia progenitors could also explain their relative faintness.

Garth

Last edited: Feb 9, 2007
10. Feb 9, 2007

### oldman

Statistical sophistry

When this kind of data is simply plotted (as in Fig 10.7 of Kirschner's Extravagent Universe), rather than statistically analysed, it is difficult to ignore its considerable scatter and become convinced that it is of model-deciding significance.

Small effects based on statistical analyses often dissolve as observations and/or analysis improve. Weber's original claims to have observed gravitational waves are one ancient example I can think of.

11. Feb 9, 2007

### Locrian

Well obbviously we understand IaSN at least well enough such that we aren't getting wild fluctuations that prevent us from making a plot at all. It seems clear to me they are some sort of standard candle - all one can say is that we're misreading them, which to me is more specific. In reference to changing chemistry - is there any reason to believe that all objects that go IaSN have the same chemistry? I mean, is the variation in chemistry over the distance of low to high z SN greater than random variation between Ia dwarfs of the same z?

Last edited: Feb 9, 2007
12. Feb 9, 2007

### Locrian

That's very interesting. However, I don't think it has any value until this "intrinsic" redshift has been measured separately. I'm sorry for not doing the research on my own - do they argue this has been independently measured?

13. Feb 9, 2007

### Locrian

Thanks for mentioning this, I will look into it.

14. Feb 9, 2007

### matt.o

Ok, I'll re-phrase: Where should the effects of the intrinsic redshift be most prevalent? Or, how much does this intrinsic redshift contribute to the observed redshift and is the intrinsic redshift the same for each galaxy?

I think it is important to note that whilst SNIa evolution is an ongoing research subject (it isn't being swept under the rug; just do an author search for 'salvo' on adsabs.harvard.edu), I think it is also important to note that other studies such as baryon acoustic ocillations and WMAP all show convergence to a dark energy dominated universe. Hopefully in the near future the error bars will be tightened and there will be better constraints.

15. Feb 10, 2007

### Garth

Hi matt.o.
But this analysis is model dependent, and the OP link paper suggested that no model could be made to fit if the SNe Ia were standard candles. What should we make of this strong assertion?

Garth

Last edited: Feb 10, 2007
16. Feb 15, 2007

### Garth

In Tuesday's ArXiv, Mazzali, Ropke, Benetti and Hillebrandt's paper (Journal-ref: Science 315, 825 (2007) DOI: 10.1126/science.1136259): A Common Explosion Mechanism for Type Ia Supernovae.
(emphasis mine)
These progenitors were of the same mass and were all 'nearby'.
But how can we be sure that at further distances z ~ 1 the masses of the progenitors and/or the N-56 abundance are the same as the nearby ones?

Garth

Last edited: Feb 16, 2007
17. Feb 28, 2007

### Garth

There may also be two separate populations of SNe Ia Two populations of progenitors for type Ia SNe?.

Furthermore, the Fe abundance seems to be evolving over cosmological history: On the evolution of the Fe abundance and of the Type Ia SN rate in clusters of galaxies. Note this is an example of chemical evolution over cosmological time. The Ni-56 is produced from Carbon and Oxygen burning. Evolution of one element, Iron, might also signify evolution of these SNe Ia fuels thus affecting the amount of Ni-56 and the intrinisic maximum of the luminosity curve.

Garth

Last edited: Feb 28, 2007
18. Jun 1, 2007

### Garth

From today's ArXiv:

SN 2005hj: Evidence for Two Classes of Normal-Bright SNe Ia and Implications for Cosmology by Robert Quimby, Peter Höflich & J. Craig Wheeler., accepted for publication in Ap.J.
Which highlights uncertainties in the modelling of the SNe Ia.

Garth

Last edited: Jun 1, 2007
19. Jun 3, 2007

### Chronos

Not terribly discordant. The physics behind SNe 1a are fairly well understood, so the candle model is pretty robust. What is not well understood is extinction effects.

20. Dec 6, 2007

### Garth

A recent paper accepted for publication in a special edition of General Relativity and Gravitation by Professor Sarkar (Oxford University) Is the evidence for dark energy secure? suggests alternative explanations for the standard interpretation of cosmological data, including SNe Ia, which normally support the hypothesis of DE.

He says:
He continues:
(Emphasis mine)

Garth