Type Ia Supernovae: Implications for Cosmology

[wolram]

http://arxiv.org/abs/astro-ph/0608324

Cosmological Implications of the Second Parameter of Type Ia Supernovae
Authors: Philipp Podsiadlowski (Oxford), Paolo A. Mazzali (MPA, Munich; Trieste), Pierre Lesaffre (Oxford, Cambridge, Paris), Christian Wolf (Oxford), Francisco Forster (Oxford)
Comments: 10 pages, 6 figures, constructive comments welcome

Theoretical models predict that the initial metallicity of the progenitor of a Type Ia supernova (SN Ia) affects the peak of the supernova light curve. This can cause a deviation from the standard light curve calibration employed when using SNe Ia as standardizable distance candles and, if there is a systematic evolution of the metallicity of SN Ia progenitors, could affect the determination of cosmological parameters. Here we show that this metallicity effect can be substantially larger than has been estimated previously, when the neutronisation in the immediate pre-explosion phase in the CO white dwarf is taken into account, and quantitatively assess the importance of metallicity evolution for determining cosmological parameters. We show that, in principle, a moderate and plausible amount of metallicity evolution could mimic a lambda-dominated, flat Universe in an open, lambda-free Universe. However, the effect of metallicity evolution appears not large enough to explain the high-z SN Ia data in a flat Universe, for which there is strong independent evidence, without a cosmological constant. We also estimate the systematic uncertainties introduced by metallicity evolution in a lambda-dominated, flat Universe. We find that metallicity evolution may limit the precision with which Omega_m and w can be measured and that it will be difficult to distinguish evolution of the equation of state of dark energy from metallicity evolution, at least from SN Ia data alone.

May be not much, just another question mark.

 

[wolram]

Double edged sword.

http://arxiv.org/abs/astro-ph/0608351

The impact of neutrino masses on the determination of dark energy properties
Authors: Axel De La Macorra, Alessandro Melchiorri, Paolo Serra, Rachel Bean
Comments: 4 pages, 2 figures

Recently, the Heidelberg-Moscow double beta decay experiment has claimed a detection for a neutrino mass with high significance. Here we consider the impact of this measurement on the determination of the dark energy equation of state. By combining the Heidelberg-Moscow result with the WMAP 3-years data and other cosmological datasets we constrain the equation of state to -1.67< w <-1.05 at 95% c.l., ruling out a cosmological constant at more than 95% c.l.. Interestingly enough, coupled neutrino-dark energy models may be consistent with such equation of state. While future data are certainly needed for a confirmation of the controversial Heildelberg-Moscow claim, our result shows that future laboratory searches for neutrino masses may play a crucial role in the determination of the dark energy properties.

 

[wolram]

No acceleration

http://arxiv.org/abs/astro-ph/0608386

On the Absence of Cosmic Acceleration
Authors: John Middleditch
Comments: 12 pages
Report-no: LAUR 06-5685

Type Ia Supernovae (SNe) have been used by many to argue for an accelerated expansion of the universe. However, high velocity and polarized features in all nearby SNe Ia, show that the paradigm for Type Ia SNe is drastically and catastrophically invalid. By now it is also clear that an extreme version of the axisymmetry seen in SN 1987A is the correct paradigm for SNe Ia and Ic. A Ia/c is produced from the merger of two degenerate cores of common envelope WR stars, or of two CO white dwarfs. Its polar blowouts produce the observed high velocity and polarized spectral features in Ia's, and its equatorial bulge is much brighter in Ia's, due to the greater fraction of 56 Ni contained within it. These become classified as Ia's when viewed from the merger equator, and Ic's when viewed from the poles. Thus cosmology determined strictly from Ia's alone is flawed at its very foundation: the local sample is selectively biased. The problem arose with the more distant supernovae, when the high velocity polar blowout features, which initially obscure part of the Ia/c equatorial bulge, expose a greater fraction of it, particularly when viewed off the equator, during the interval when Delta m_15 is measured, leading to a smaller decrease in observed luminosity. The width-luminosity correction was thus too small, and the result was a distant SN Ia which appeared to be too faint for its redshift. When the errors introduced by this process and others are taken into account, there may be no cosmic acceleration effect in distant SNe.

 

[Garth]

These papers may indicate the confidence placed in the standard
$\Lambda$CDM model may be misplaced.

Garth

 

[wolram]

These papers may indicate the confidence placed in the standard
$\Lambda$CDM model may be misplaced.

Garth

I am not going to say anything Garth, i will just post any thing that seems interesting in this thread, unless anyone has objections.

 

[Garth]

I am not going to say anything Garth, i will just post any thing that seems interesting in this thread, unless anyone has objections.

The point is: Are these 'SN Ia' standard candles?

Such a lot in the standard model hangs on the assumption that they are.

Yet the evidence that their luminosities are known depends only on those nearby, and therefore recent, ones that are able to be calibrated. As we go back into cosmological history metallicity may be expected to change, and as your links imply this may alter their expected luminosities and call into question the conclusions based on them.

Garth

 

[wolram]

The point is: Are these 'SN Ia' standard candles?

Such a lot in the standard model hangs on the assumption that they are.

Yet the evidence that their luminosities are known depends only on those nearby, and therefore recent, ones that are able to be calibrated. As we go back into cosmological history metallicity may be expected to change, and as your links imply this may alter their expected luminosities and call into question the conclusions based on them.

Garth

May be i should ask you what is standard in cosmology, is there a standard galaxy ,star, planet, moon, if not it is difficult to understand how there can be a (standard) body in the U.

 

[Garth]

The concept of a standard candle is simply a luminous object of which we think we know the Absolute Magnitude. (Such as the Cepheid Variables)

The object's distance can then be calculated from the distance modulus.

Garth

 

[matt.o]

I think Wolram was asking a deeper question here, Garth. He is pointing out the differences in other observed phenomena such as galaxies and then questioning how there can be standard candles if things are so different.

I would just like to say that as scientists, we generally like to have a few more cards up our sleeves, hence there are other tests which point to a dark energy density of ~.7 independant of the SN1a results. Such studies include the CMB, baryon acoustic fluctuations, galaxy cluster mass function etc.

 

[SpaceTiger]

The point is: Are these 'SN Ia' standard candles?

Such a lot in the standard model hangs on the assumption that they are.

That hasn't been true for some time. Pretty much everything we infer from Type Ia SNe (so far) has been checked with other methods (e.g. CMB, LSS). In fact, it would be very strange if the results were found to be invalid after having already been found consistent with these more reliable measurements.

 

[wolram]

I think Wolram was asking a deeper question here, Garth. He is pointing out the differences in other observed phenomena such as galaxies and then questioning how there can be standard candles if things are so different.

I would just like to say that as scientists, we generally like to have a few more cards up our sleeves, hence there are other tests which point to a dark energy density of ~.7 independant of the SN1a results. Such studies include the CMB, baryon acoustic fluctuations, galaxy cluster mass function etc.

Thankyou, Matt.o,

i do not know about (baryon acoustic fluctuations) i will have to look up the
subject.

 

[Garth]

The point is: Are these 'SN Ia' standard candles?

Such a lot in the standard model hangs on the assumption that they are.

That hasn't been true for some time. Pretty much everything we infer from Type Ia SNe (so far) has been checked with other methods (e.g. CMB, LSS). In fact, it would be very strange if the results were found to be invalid after having already been found consistent with these more reliable measurements.

ST - what do you think about the OP link paper?

If SN Ia are not standard candles and the universe is not accelerating would that not alter the interpretation of the CMB and LSS data?

Garth

 

[matt.o]

Thankyou, Matt.o,

i do not know about (baryon acoustic fluctuations) i will have to look up the
subject.

Actually, I don't think baryon acoustic fluctuations have been used by themselves (yet) to constrain dark energy. The current galaxy redshift surveys don't cover enough volume. They have certainly been used in conjunction with WMAP data to constrain cosmological parameters http://arxiv.org/abs/astro-ph/0507583" paper by Chris Blake and Karl Glazebrook.

I do know of galaxy redshift surveys that are going to attempt to estimate the equation of state of the dark energy, but they are a little while off yet. There are also planned missions to survey for clusters and measure the dark energy equation of state using the cluster mass function.

 

[SpaceTiger]

ST - what do you think about the OP link paper?

The paper in the OP says the following:

We show that, in principle, a moderate and plausible amount of metallicity evolution could mimic a lambda-dominated, flat Universe in an open, lambda-free Universe. However, the effect of metallicity evolution appears not large enough to explain the high-z SN Ia data in a flat Universe, for which there is strong independent evidence, without a cosmological constant.

This doesn't suggest to me that the SN Ia results have been invalidated.

As for the Middleditch paper, I took a quick look at it and it sounds very crankish. I doubt it will make any waves.

If SN Ia are not standard candles and the universe is not accelerating would that not alter the interpretation of the CMB and LSS data?

If SNe Ia were not standard candles, why would you infer that the universe was not accelerating? The former statement would simply mean that they couldn't be used as distance indicators.

 

[Tzemach]

There are still some big holes in our understanding, maybe if we collect enough details of anomolies we will be able to figure out just what is going on out there.
Here are a couple for the collection'

APM 8279+5255 the red shift of the quasar, a vibrant galaxy with a bright central region and massive central black hole, revealed that it contained much more iron than it should for its age. The amount of iron present is greater than the amount found in our own solar system. At a fraction of the age of the solar system this quasar should contain the lower percentage of iron.

Fossil cluster RX J1416.4+2315 Current projections state that the fossil group should not have had enough time to form given the age of the universe.

 

[Garth]

If SNe Ia were not standard candles, why would you infer that the universe was not accelerating? The former statement would simply mean that they couldn't be used as distance indicators.

I was simply reverting back to the pre-'cosmic acceleration' understanding.

The acceleration or non-acceleration of the universe determined from SNe Ia at varing high z is an important handle on the behaviour and therefore nature of DE.

The consequences of them not being standard candles would therefore be rather significant. Tzemach has highlighted again the Age problem question, I think there is a degeneracy in the interpretation of the data that may be resolved by attention to these anomalies.

Is there an age problem at high z?
Are SNe Ia standard candles?
Is there a genuine deficiency at low-l mode in the WMAP anisotropy power spectrum?
Just a few questions to chew over...

Garth

 

[SpaceTiger]

I was simply reverting back to the pre-'cosmic acceleration' understanding.

The acceleration or non-acceleration of the universe determined from SNe Ia at varing high z is an important handle on the behaviour and therefore nature of DE.

The consequences of them not being standard candles would therefore be rather significant.

It's not clear to me that your above statements really make that case. It would have made a big difference historically, but with the high-precision CMB and LSS measurements we have now, I don't think you'd see many people jumping ship from standard cosmology.

 

[Garth]

It's not clear to me that your above statements really make that case. It would have made a big difference historically, but with the high-precision CMB and LSS measurements we have now, I don't think you'd see many people jumping ship from standard cosmology.

Well ST, surely a project such as Destiny

Destiny is a simple, direct, low cost mission to determine the properties of dark energy by obtaining a cosmologically deep supernova (SN) type Ia Hubble diagram. Operated at L2, its science instrument is a 1.65m space telescope, featuring a grism-fed near-infrared (NIR) (0.85-1.7micron) survey camera/spectrometer with a 0.12 square degree field of view. During its two-year primary mission, Destiny will detect, observe, and characterize ~3000 SN Ia events over the redshift interval 0.4<z<1.7 within a 3 square degree survey area. In conjunction with ongoing ground-based SN Ia surveys for z<0.8, Destiny mission data will be used to construct a high-precision Hubble diagram and thereby constrain the dark energy equation of state from a time when it was strongly matter-dominated to the present when dark energy dominates.

depends on the assumption that SNe Ia are standard candles?

Are you saying that if, for the sake of argument, they prove to be intrinsically fainter (say) at high z, then the interpretation of the high precision WMAP and LSS data would not be affected?

Or do you think that WMAP, LSS, etc. have so proved cosmic acceleration independently of SNe Ia that the there is no question about it, and consequently SNe Ia have been verified to be standard candles?

Garth

 

[SpaceTiger]

Are you saying that if, for the sake of argument, they prove to be intrinsically fainter (say) at high z, then the interpretation of the high precision WMAP and LSS data would not be affected?

Again, this depends crucially on the distinction between them not being standard candles and them being renormalized. If they were renormalized and subsequently showed no acceleration, then that would be a serious problem for mainstream cosmology in general. That alone likely wouldn't be enough to convince folks (after all, it would also demonstrate the unreliability of supernovae). However, if subsequent measurements with other distance indicators gave the same result, the mainstream model would have to be changed.

If the supernovae were just shown to be unreliable as standard candles, then yes, I'm saying the interpretation would likely remain the same. Your choice of words in the above doesn't make it clear which case you're referring to.

Or do you think that WMAP, LSS, etc. have so proved cosmic acceleration independently of SNe Ia that the there is no question about it, and consequently SNe Ia have been verified to be standard candles?

Those data sets do not directly prove acceleration, but they do suggest it. Believe it or not, $\Lambda CDM$ was under serious consideration even prior to the supernova results because of COBE CMB measurements.

 

[matt.o]

Those data sets do not directly prove acceleration, but they do suggest it. Believe it or not, $\Lambda CDM$ was under serious consideration even prior to the supernova results because of COBE CMB measurements.

Exactly. From COBE, it was known we live in an $$\Omega$$ = 1 Universe, but the observed matter density only made up ~.3 of the total density. People were considering a cosmological constant to make up the rest of the energy density and along came the SN 1a results!

 

[Garth]

Exactly. From COBE, it was known we live in an $$\Omega$$ = 1 Universe, but the observed matter density only made up ~.3 of the total density. People were considering a cosmological constant to make up the rest of the energy density and along came the SN 1a results!

But the conclusion that we live in a spatially flat universe is not proven by COBE or WMAP, as I have emphasised many times the CMB data is angular in nature, and as conformal transforms are angle preserving (by definition), the data only establishes that we live in a conformally flat universe, of which $$\Omega_{total}$$ = 1 is only one option.

Garth

 

[SpaceTiger]

But the conclusion that we live in a spatially flat universe is not proven by COBE or WMAP, as I have emphasised many times the CMB data is angular in nature, and as conformal transforms are angle preserving (by definition), the data only establishes that we live in a conformally flat universe, of which $$\Omega_{total}$$ = 1 is only one option.

AFAIK, WMAP data is only consistent with a (nearly) spatially flat FRW model. If one wishes to abandon GR or the cosmological principle, there are probably other solutions, but you should know as well as anyone that it will take more than the breakdown of SNe as standard candles to make that happen.

 

[Garth]

AFAIK, WMAP data is only consistent with a (nearly) spatially flat FRW model. If one wishes to abandon GR or the cosmological principle, there are probably other solutions, but you should know as well as anyone that it will take more than the breakdown of SNe as standard candles to make that happen.

Indeed, but an indication that SNe Ia are not standard candles may be a sign, along with the other questions posed above, that an open mind is the best policy!

Garth

 

[Garth]

However, if subsequent measurements with other distance indicators gave the same result, the mainstream model would have to be changed.

Such as indicated by this podcast report in Scientific American?

In this episode, Scientific American editor George Musser explains recent research that could mean that the entire universe is 15 percent bigger and about two billion years older than previously thought.

ie. H₀ = 63 km/sec/Mpsc.

Garth

 

[matt.o]

You really like to pick and choose, don't you Garth? How about http://arxiv.org/abs/astro-ph/0512349" one? It has more than on data point too!

 

[Garth]

Agreed, I was just pointing out that all observations do not yet agree on a 'precision cosmology', and that some systematic error may be at work!

Garth

 

[matt.o]

Agreed, I have been thinking about this systematics issue with SN1a's and I think a good way to test for subtle differences in types of SN1a's (possibly voiding the SN1a as an accurate distance indicator) is to look for galaxies with multiple SN1a's and test to see if the measured distances are the same. Or possibly use clusters of galaxies to study multiple SN1a's in different galaxies within the cluster, hence at the same distance (within ~2Mpc). This may have already been done, but if there were different species of SN1a, there should be some significant variance in the distances measured.

 

[SpaceTiger]

Such as indicated by this podcast report in Scientific American?

No, I'm referring to measurements of acceleration. The Hubble constant can shift without the need for a new paradigm.

 

[franznietzsche]

Agreed, I have been thinking about this systematics issue with SN1a's and I think a good way to test for subtle differences in types of SN1a's (possibly voiding the SN1a as an accurate distance indicator) is to look for galaxies with multiple SN1a's and test to see if the measured distances are the same. Or possibly use clusters of galaxies to study multiple SN1a's in different galaxies within the cluster, hence at the same distance (within ~2Mpc). This may have already been done, but if there were different species of SN1a, there should be some significant variance in the distances measured.

Not if the variance was based on local properties--like composition. Supernovae in the same region would date to similar times and see similar composition effects.

 

[matt.o]

Not if the variance was based on local properties--like composition. Supernovae in the same region would date to similar times and see similar composition effects.

This is true, but I think it is still a worthwhile experiment. Besides, you would expect the composition of galaxies within a cluster to vary since we can observe many different types of galaxies within a few Mpc radius at a similar distance.

 

[franznietzsche]

This is true, but I think it is still a worthwhile experiment. Besides, you would expect the composition of galaxies within a cluster to vary since we can observe many different types of galaxies within a few Mpc radius at a similar distance.

Different types of galaxies does not necessarily mean different types of compositions. Unless we can directly measure the composition (we can barely do that well for stars in our own galaxy, even for the sun). However, I do agree it would be worthwhile. If supernovae in the same region were found to differ significantly, that would be very important. But finding that they don't differ wouldn't tell you a whole lot--thats all I'm saying.

 

[matt.o]

Different types of galaxies does not necessarily mean different types of compositions. Unless we can directly measure the composition (we can barely do that well for stars in our own galaxy, even for the sun). However, I do agree it would be worthwhile. If supernovae in the same region were found to differ significantly, that would be very important. But finding that they don't differ wouldn't tell you a whole lot--thats all I'm saying.

In fact, galaxies with high rates of star formation are known to have higher obscuration (ie. metallicity) - it depends on how you define a galaxy as different. It is easy to measure the metallicity from a galaxy spectra and hence composition, in fact this has already been studied to correlate with SN1a brightness http://arxiv.org/abs/astro-ph/0508180" . We just talk about 'composition' in a more broad sense when discussing galaxies. It is also well known that metallicity varies from point to point in a galaxy, radial gradients are seen in metallicities especially in spirals.

 

[franznietzsche]

In fact, galaxies with high rates of star formation are known to have higher obscuration (ie. metallicity) - it depends on how you define a galaxy as different. It is easy to measure the metallicity from a galaxy spectra and hence composition, in fact this has already been studied to correlate with SN1a brightness http://arxiv.org/abs/astro-ph/0508180" . We just talk about 'composition' in a more broad sense when discussing galaxies. It is also well known that metallicity varies from point to point in a galaxy, radial gradients are seen in metallicities especially in spirals.

A couple of things:

1) We're talking about galaxies at very high red shifts, low metallicities should be universal (on the other hand, relative variations should be higher in early stars as well).
2) SNIa are caused by white dwarfs in a binary pair with another star. The dwarfs accumulate the envelope material of the other star before exploding.

To be honest, we do not clearly understand how the envelope composition will differ from the overall composition of the stars--this is in fact loosely related to the work I am doing in Los Alamos currently.

It is not easy to measure metallicity accurately--at least not to the degree of accuracy needed in asteroseismology. One of the major problems in helioseismology right now is that the solar metallicity is apparently much lower than previously thought (factor of 1.5)--and our models no longer agree as closely. Of course, I'm talking about disagreements between prediction and measurement of something like 1.5% (compared to less than .5% previously) which greatly exceeds the error bars on the measurements. Accurately determining metallicities is difficult, because you have to make many assumptions. In the case of the new solar metallicities, using 3-D hydro simulations to deduce them from the observed spectral lines resulted in the new values. Its all a question of error bars, and how sensitive the supernovae yields may be to composition.

 

[matt.o]

Oh, ok. We have our wires crossed on the definition of composition. I was using the term loosely to describe the larger scale metallicities in a galaxy, hence I misinterpreted your post #31. Being a galaxy/LSS person, local to me means not very local to you!

In any case, my post #27 still stands. A large sample of distances derived from multiple SN1a's in the same galaxys/galaxy clusters should give us a good idea as to the systematics at play.

 

[franznietzsche]

Oh, ok. We have our wires crossed on the definition of composition. I was using the term loosely to describe the larger scale metallicities in a galaxy, hence I misinterpreted your post #31. Being a galaxy/LSS person, local to me means not very local to you!

Ah, ok.

In any case, my post #27 still stands. A large sample of distances derived from multiple SN1a's in the same galaxys/galaxy clusters should give us a good idea as to the systematics at play.

I don't disagree, with the principle, but I think its not as useful as you described (perhaps because I'm overestimating your confidence in the measurement?). If such a measurement found significant variations in the derived distances from SN1a's in the same galaxy, that would be important. However, I don't think that a finding of no major variation means in anyway that there aren't potentially significant systematic variations in power output.