The Universe's Expansion May Be Slowing Down, Not Speeding Up ?

[TheVat]

am not sure where this progenitor factor came in. Is there consensus on it's significance?

AFAICT, spotting a progenitor (as has been done with RSG supernovae) is critical
to understanding explosion mechanisms and sound analysis of the light curve. Bear in mind that the 1a SN was considered to produce a fairly consistent peak luminosity because of the fixed critical mass at which it will explode (Chandrasekhar mass). So this mass issue does, imho, a lot of theoretical hod carrying for the whole standard candle system. The system is built on a white dwarf gradually accreting mass from a binary companion - it's a hypothesis that a white dwarf's core will reach the ignition temperature for carbon fusion as it approaches the Chandrasekhar mass. Within a few seconds of initiation of nuclear fusion, a substantial fraction of the matter in the white dwarf undergoes a runaway reaction and ka-boom. My point is how hypothetical this is, without us having ever seen a progenitor for this class of SN.

When you look at the diversity in supernova light curves, spectral features and explosion geometries, you see, to paraphrase Bill Clinton, "it's the progenitor, stupid." So mass, composition, stellar history (if that's the term?), binary interactions, etc. So how much, I ask, have we really known about these features of the 1a progenitors? Especially when age makes a difference.*

Killjoy's OP paper has sort of released some pent up irritation I had with the standard model.



* Younger white dwarf versus older white dwarf. So Peter Dinklage versus Kenny Baker, right?

 

[exchemist]

AFAICT, spotting a progenitor (as has been done with RSG supernovae) is critical
to understanding explosion mechanisms and sound analysis of the light curve. Bear in mind that the 1a SN was considered to produce a fairly consistent peak luminosity because of the fixed critical mass at which it will explode (Chandrasekhar mass). So this mass issue does, imho, a lot of theoretical hod carrying for the whole standard candle system. The system is built on a white dwarf gradually accreting mass from a binary companion - it's a hypothesis that a white dwarf's core will reach the ignition temperature for carbon fusion as it approaches the Chandrasekhar mass. Within a few seconds of initiation of nuclear fusion, a substantial fraction of the matter in the white dwarf undergoes a runaway reaction and ka-boom. My point is how hypothetical this is, without us having ever seen a progenitor for this class of SN.

When you look at the diversity in supernova light curves, spectral features and explosion geometries, you see, to paraphrase Bill Clinton, "it's the progenitor, stupid." So mass, composition, stellar history (if that's the term?), binary interactions, etc. So how much, I ask, have we really known about these features of the 1a progenitors? Especially when age makes a difference.*

Killjoy's OP paper has sort of released some pent up irritation I had with the standard model.



* Younger white dwarf versus older white dwarf. So Peter Dinklage versus Kenny Baker, right?

I've had a quick look into this and found a paper from 2 years ago that suggests modelling based on attenuation by galactic dust might account for why SN1a in older galaxies may be brighter than in younger ones: https://academic.oup.com/mnras/article/520/4/6214/7036804?login=false
But that would a galaxy effect rather than a progenitor star effect. The sources of potential variation look pretty complicated. Analysis seems to be based on collating observations rather than theoretical modelling of the physics of supernovae.

 

[Pinball1970]

I've had a quick look into this and found a paper from 2 years ago that suggests modelling based on attenuation by galactic dust might account for why SN1a in older galaxies may be brighter than in younger ones: https://academic.oup.com/mnras/article/520/4/6214/7036804?login=false
But that would a galaxy effect rather than a progenitor star effect. The sources of potential variation look pretty complicated. Analysis seems to be based on collating observations rather than theoretical modelling of the physics of supernovae.

Some info on the affect of binary systems.

FROM Ai

"Progenitor star system

• Binary system: A Type Ia supernova is widely agreed to originate from a binary star system, as a lone white dwarf requires a companion to trigger an explosion.
• White dwarf: The central component is a carbon-oxygen white dwarf that has run out of nuclear fuel.
• Accretion: The white dwarf accretes matter from a companion star, which can be either a non-degenerate star or another white dwarf. This process adds mass to the white dwarf.

Key models

• Single-degenerate (SD) model: The white dwarf accretes matter from a non-degenerate companion star, such as a red giant or main-sequence star.
• Double-degenerate (DD) model: Two white dwarfs in a binary system spiral inward due to gravitational wave radiation, eventually merging and exploding. "

A paper from 2006 here.

https://academic.oup.com/mnras/article/370/2/773/968117

 

[Pinball1970]

Ai part 2

"Impact of the progenitor system on the supernova
Explosion trigger: The companion's mass-transfer mechanism dictates how the white dwarf gains mass and whether it triggers a detonation or a deflagration.
Supernova characteristics: The progenitor system's properties can affect the supernova's observed light curve shape, color, and luminosity. For example, a massive amount of circumstellar matter from a WD+MS system can lead to a "Type IIn" subclass of supernova.
Population difference: The existence of different progenitor populations (e.g., younger vs. older stars) can explain the different rates of Type Ia supernovae in galaxies"

Me: The second part here, "Colour and luminosity." Feature in calculating the intensity and therefore distance.

 

[exchemist]

Ai part 2

"Impact of the progenitor system on the supernova
Explosion trigger: The companion's mass-transfer mechanism dictates how the white dwarf gains mass and whether it triggers a detonation or a deflagration.
Supernova characteristics: The progenitor system's properties can affect the supernova's observed light curve shape, color, and luminosity. For example, a massive amount of circumstellar matter from a WD+MS system can lead to a "Type IIn" subclass of supernova.
Population difference: The existence of different progenitor populations (e.g., younger vs. older stars) can explain the different rates of Type Ia supernovae in galaxies"

Me: The second part here, "Colour and luminosity." Feature in calculating the intensity and therefore distance.

But surely this is just about the types of supernova produced, not an explanation of what could make individual type 1a supernovae differ from one another, depending on the age of their progenitor? Or am I misreading it?

 

[TheVat]

But surely this is just about the types of supernova produced, not an explanation of what could make individual type 1a supernovae differ from one another, depending on the age of their progenitor? Or am I misreading it?

I guess some of my problem lies in how they are precisely classifying observed SNs and getting a reliable 1a rating, and also the metal content changes with stellar aging, and does so differently in different star classes. Maybe I'm wrong on this, but I see too many potential factors tweaking the luminosity to believe in that standard candle. And how do they rule out circumstellar matter in the 1a - spectroscopically, I guess? Without ever seeing a progenitor there seems to many effects in play that can't be pinned down better. And wife has to shut off wifi so I'm offline for a bit.

 

[exchemist]

I guess some of my problem lies in how they are precisely classifying observed SNs and getting a reliable 1a rating, and also the metal content changes with stellar aging, and does so differently in different star classes. Maybe I'm wrong on this, but I see too many potential factors tweaking the luminosity to believe in that standard candle. And how do they rule out circumstellar matter in the 1a - spectroscopically, I guess? Without ever seeing a progenitor there seems to many effects in play that can't be pinned down better. And wife has to shut off wifi so I'm offline for a bit.

I thought a white dwarf SN1a candidate had a composition determined by its inability to fuse carbon, so it wouldn’t have anything heavier in it, regardless of its age when it blew up.

 

[TheVat]

I thought a white dwarf SN1a candidate had a composition determined by its inability to fuse carbon, so it wouldn’t have anything heavier in it, regardless of its age when it blew up.

Well I'm starring from Chul Chung et al....

The researchers found with a 5.5 sigma confidence – beyond the gold standard threshold of science – that Type Ia supernova brightness depends on the age of their progenitor stars. This means that they have found with 99.9999999 percent confidence that supernovae from younger stellar populations appear systematically fainter, while those from older populations appear brighter.

So I'm looking at what's in play. Is some of it an effect of the host galaxy, and not the WD itself? Maybe. And maybe better resolved with more observation. When they talk of "mass step," that's fancy astrophysics talk for total mass of the host galaxy. Most of the host discussion in that paper is about how overall mass, metallicity, and so on of the galaxy have been ruled out by the data as having any significant effect.

Chung reports

They also found that two subgroups based on other host properties – such as stellar mass, metallicity, and dust content – exhibit only insignificant offsets in the WLR and CLR, suggesting that progenitor age is most likely the root cause of the reported correlations between host properties and HR.

So is he saying metallicity is not important in the host galaxy overall or is it also not important in the progenitor? I kept reading. It's unclear, and beyond the scope of that paper.

Metallicity does vary between white dwarfs, and the overall metal content of a host galaxy will affect that, due to accretion and so on. Younger galaxies would presumably have less metal, overall, and more of it light metals like lithium or beryllium. So we have 1a SNs that seem to be intrinsically fainter (lower absolute magnitude) in younger galaxies, and this is caused by something happening with the stage of stellar evolution where a WD can fuse carbon and oxygen and commence a runaway fusion. Are there metals in play, like lithium? Fuse it with a proton and you get beryllium 8. Could be negligible - I'm not up on that stuff. Could a white dwarf suck in a planet or accretion disk or siphon matter from a companion star and end up with more metals on hand when its degenerate core (see electron degeneracy pressure, if some of you are unfamiliar) is overcome by mass accretion?

 

[Pinball1970]

But surely this is just about the types of supernova produced, not an explanation of what could make individual type 1a supernovae differ from one another, depending on the age of their progenitor? Or am I misreading it?

Just to pull this back a bit because there have been a few posts since mine.
My understanding is that Type 1a SN are used as standard candles because they are all the same and they are very bright.
This means they can be seen across large cosmic distances and if one is dimmer than another it must be further away.

The system the SN happen to be in, has been factored in to the calculations in this paper.

The types of systems are outlined in post #23 but I have not read anything yet that explains exactly how the luminosity is affected.

Post 4 by Ibix in the thread below says paragraph two of my post above is wrong according to the paper.
They cannot be used as standard candles without factoring this other stuff in.

Thread 'Strong Progenitor Age Bias in Supernova Cosmology' https://www.physicsforums.com/threads/strong-progenitor-age-bias-in-supernova-cosmology.1082899/

 

[Pinball1970]

So is he saying metallicity is not important in the host galaxy overall or is it also not important in the progenitor? I kept reading. It's unclear, and beyond the scope of that paper.

I noted that and it makes the paper (more) difficult to read.

 

[Pinball1970]

"The first notable evidence of an age bias in the SN distance scale was presented based on high-precision, spectroscopic observations of early-type host galaxies. In this study, three different population synthesis models were applied, each producing consistent results showing that the post-standardization magnitudes of SNe from younger host galaxies are systematically fainter than those from older galaxies."

 

[Pinball1970]

Jesus that quote took about ten edits and five goes to post it.

Justification regarding including this fiddle factor. The studies went from 3 sigma to 5.5 sigma.
Frustratingly it does not say what it actually is, just that the age (of the galaxy/ progenitor) is significant and has to be factored in.

 

[Pinball1970]

Apologies that this is so fragmented, I'm having trouble this morning.
I will continue to look into this progenitor side of things, where is an astrophysicist when you need one? Jarek Duda
Since this paper will have an impact (huge) on Cosmology, we should expect follow up and push back.
One thing I did notice, Gupta is cited in the reference list, I will check if this is the same Gupta that proposed that the Universe is 26 billion years old in a paper 2023 ish.

 

[exchemist]

Well I'm starring from Chul Chung et al....



So I'm looking at what's in play. Is some of it an effect of the host galaxy, and not the WD itself? Maybe. And maybe better resolved with more observation. When they talk of "mass step," that's fancy astrophysics talk for total mass of the host galaxy. Most of the host discussion in that paper is about how overall mass, metallicity, and so on of the galaxy have been ruled out by the data as having any significant effect.

Chung reports


So is he saying metallicity is not important in the host galaxy overall or is it also not important in the progenitor? I kept reading. It's unclear, and beyond the scope of that paper.

Metallicity does vary between white dwarfs, and the overall metal content of a host galaxy will affect that, due to accretion and so on. Younger galaxies would presumably have less metal, overall, and more of it light metals like lithium or beryllium. So we have 1a SNs that seem to be intrinsically fainter (lower absolute magnitude) in younger galaxies, and this is caused by something happening with the stage of stellar evolution where a WD can fuse carbon and oxygen and commence a runaway fusion. Are there metals in play, like lithium? Fuse it with a proton and you get beryllium 8. Could be negligible - I'm not up on that stuff. Could a white dwarf suck in a planet or accretion disk or siphon matter from a companion star and end up with more metals on hand when its degenerate core (see electron degeneracy pressure, if some of you are unfamiliar) is overcome by mass accretion?

I took both papers - the new one and I one I found from 2 years ago - to be suggesting there is more dust in younger galaxies and the modelling in the new paper indicates this can just about account for the observed discrepancy in brightness, though they are not ruling out other contributing factors.

But perhaps I’d better read them again in the light of the thread from the physics forum that Pinball1970 has helpfully linked.

Whatever the reasons, this finding puts the cat among the cosmological pigeons regarding Dark Energy, which looks to me like a promising development.

 

[exchemist]

Apologies that this is so fragmented, I'm having trouble this morning.
I will continue to look into this progenitor side of things, where is an astrophysicist when you need one? Jarek Duda
Since this paper will have an impact (huge) on Cosmology, we should expect follow up and push back.
One thing I did notice, Gupta is cited in the reference list, I will check if this is the same Gupta that proposed that the Universe is 26 billion years old in a paper 2023 ish.

I don’t think we’ll get much out of him. He’s no astrophysicist and seems to have a one track fixation with white holes. Janus58 would be the man. But he’s only a very occasional visitor these days.

 

[Pinball1970]

I don’t think we’ll get much out of him. He’s no astrophysicist and seems to have a one track fixation with white holes. Janus58 would be the man. But he’s only a very occasional visitor these days.

Right Janus not Jarek. I think Janus is a PF member too.

It is strange that a paper like this, a potential game changer, holds little to no interest to posters like Jarek.
One quick irrelevant regurgitation of WH with a schematic and that's it.

 

[Jarek Duda]

This is discussion about Big Crunch, which is basically time reversed Big Bang - as after Big Bang there is tendency to form black holes, before Big Crunch there would be symmetric to form our white holes ... as very lone shining points.

 

[exchemist]

This is discussion about Big Crunch, which is basically time reversed Big Bang - as after Big Bang there is tendency to form black holes, before Big Crunch there would be symmetric to form our white holes ... as very lone shining points.

No it isn’t. At all.

 

[geordief]

No it isn’t. At all.

Is that because it could decelerate to a steady state w/o expansion or contraction ?

 

[exchemist]

Is that because it could decelerate to a steady state w/o expansion or contraction ?

This is all getting way ahead of the thread subject, surely? The implication of this work, if confirmed, is that the rate of expansion may not after all be accelerating. But it is still expanding.