Lambda-CDM theory - Woo or not?

[Michael Mozina]

Stellar physics is quite well understood. In particular, the relationship between the mass of a star and its luminosity is known (both from data and theory). So unless you want to invent some new physics that allows stars to have a different mass/luminosity relationship, you don't get to choose that. All you get to choose is the number of stars with any given mass, with the constraint that the total gives the total luminosity you're after.

If you invent some new physics that allows a new type of star, that's non-baryonic matter.

But I sometimes forget I'm talking to someone that believes the sun has a solid iron surface, despite the fact that its surface temperature is about 4 times the melting point of iron. I suppose someone willing to believe something that far out in lunatic wingnut land isn't going to be impressed by mass/luminosity relations of main sequence stars?

The only parts that are relevant in your post are the parts that I highlighted and the fact that I simply doubled the NUMBER of stars so the TOTAL is double.

Did you miss that part what I explained to Tim that I wasn't doubting that his method worked, I simply noted there are multiple ways to achieve the same effect?

Bashing the skeptic too sol? Really? I'm disappointed.

 

[sol invictus]

The only parts that are relevant in your post are the parts that I highlighted and the fact that I simply doubled the NUMBER of stars so the TOTAL is double.

OK - so your proposal is to simply double the star population in every galaxy?

First of all, I think that's almost certainly ruled out on the basis of observed total luminosity alone. Second, in the Milky way we can directly image lots of stars, so we know what the number density is at least in our vicinity. Are you just going to assume that the local density is 1/2 the average density for some reason? Third, doubling the number of stars does almost nothing to solve the missing mass problem. I'm not sure what the mass fraction of ordinary matter in stars is, but it's a small fraction of the total baryonic mass, and there's 5 or 6 times as much dark matter as there is baryonic matter. So you'd still be missing almost as much mass as you were before you doubled the number of stars. Fourth, none of the press releases you linked to make anything like such a proposal - for reasons related to those above, and probably for other reasons I didn't think of.

 

[Michael Mozina]

OK - so your proposal is to simply double the star population in every galaxy?

First of all, I think that's almost certainly ruled out on the basis of observed total luminosity alone.

I think you have that backwards. The total luminosity is known to be twice as high as first predicted. It's that very observation that makes it likely IMO.

Second, in the Milky way we can directly image lots of stars, so we know what the number density is at least in our vicinity.

That is just our vicinity however, and only in our own galaxy.

Are you just going to assume that the local density is 1/2 the average density for some reason?

No, we'll get to the next paper in a minute, but first things first....

Third, doubling the number of stars does almost nothing to solve the missing mass problem.

Well, from my perspective, any and all improvement in terms of pure empirical physics is a pretty good start.

I'm not denying that the fact that this doesn't resolve all the mass problems, I'm simply noting that there are ways to MINIMIZE the data or to MAXIMIZE the data in terms of identifying "missing mass". Shouldn't we be actively trying to close the gaps of our "missing mass" as much as possible and maximizing our assumptions in favor of "normal" matter?

 

[Tubbythin]

OK - so your proposal is to simply double the star population in every galaxy?

First of all, I think that's almost certainly ruled out on the basis of observed total luminosity alone. Second, in the Milky way we can directly image lots of stars, so we know what the number density is at least in our vicinity. Are you just going to assume that the local density is 1/2 the average density for some reason? Third, doubling the number of stars does almost nothing to solve the missing mass problem. I'm not sure what the mass fraction of ordinary matter in stars is, but it's a small fraction of the total baryonic mass, and there's 5 or 6 times as much dark matter as there is baryonic matter. So you'd still be missing almost as much mass as you were before you doubled the number of stars. Fourth, none of the press releases you linked to make anything like such a proposal - for reasons related to those above, and probably for other reasons I didn't think of.

Not been keeping up to date so apologies if I'm talking nonsense or repeating something already said or missing the argument from the last few posts but... doesn't adding more stars mean the universe require more dark matter? At least, I thought that was the case if the 'new' stars were placed in the same distribution as the known stars?

 

[sol invictus]

I think you have that backwards. The total luminosity is known to be twice as high as first predicted. It's that very observation that makes it likely IMO.

Nope. That observation makes it impossible.

I assume you're referring to this paper: http://iopscience.iop.org/1538-4357/678/2/L101/pdf/1538-4357_678_2_L101.pdf

Look at Fig. 4. The orange line is the observed luminosity of stars as a function of wavelength. The black line is the true (i.e. before being absorbed by dust) luminosity according to their model. Notice how they coincide almost perfectly once you get 2 micrometers or so? That's because dust hardly absorbs starlight at all at those longer wavelengths. But your proposal would double the luminosity at all wavelengths, which is not at all consistent with observation.

So what do you do instead? You change the mass function in some other way - and according to the authors of the paper, if you do it in a way consistent with data, it increases the total mass in stars by only about 20%.

That is just our vicinity however, and only in our own galaxy.

Which is more than adequate for detecting the gravitational effects of dark matter. And there is far less uncertainty in the observations, because things in our galaxy are relatively close.

 

[sol invictus]

Not been keeping up to date so apologies if I'm talking nonsense or repeating something already said or missing the argument from the last few posts but... doesn't adding more stars mean the universe require more dark matter? At least, I thought that was the case if the 'new' stars were placed in the same distribution as the known stars?

Maybe - I'm not sure which observations you have in mind or what you're holding fixed. I think if you just consider galactic rotation curves, adding more stars must reduce the amount of dark matter needed (because it increases the amount of mass interior to the orbit of every star, thereby making those orbits faster).

I guess if you doubled the number of stars and there was no other matter, it would increase the average orbital velocity of every star by a factor of root(2), but leave the shape of the rotation curve unchanged. Obviously that is totally inconsistent with observation, but it seems to me it requires less DM to fix.

 

[Tubbythin]

Maybe - I'm not sure which observations you have in mind or what you're holding fixed. I think if you just consider galactic rotation curves, adding more stars must reduce the amount of dark matter needed (because it increases the amount of mass interior to the orbit of every star, thereby making those orbits faster).

I guess if you doubled the number of stars and there was no other matter, it would increase the average orbital velocity of every star by a factor of root(2), but leave the shape of the rotation curve unchanged. Obviously that is totally inconsistent with observation, but it seems to me it requires less DM to fix.

I was thinking... if you have the matter distribution based on the observed luminosity distribution (central bulge plus extensive disc) you would expect rotation curves to drop off away from the central bulge. But they stay flatish. So a dark matter halo is proposed. From that I was thinking that if you just add more luminous matter in the known luminous distribution (central bulge plus disc) you don't solve the problem at all. And you would in fact need more dark matter in the halo to get the flat rotation curve.

 

[Reality Check]

Well, from my perspective, any and all improvement in terms of pure empirical physics is a pretty good start.

Well, from science's perspective, any and all improvement in terms of pure empirical physics is a pretty good start.
It is a pity that you are talking about stars and still cannot understand that they are a small % of the visible mass.
The distribution of galaxy luminosities, stellar and baryonic masses, and galaxy sizes from SDSS and 2MASS SEDs (2004)
Bell, E. F.; McIntosh, D. H.; Gyory, Z.; Trujillo, I.; Katz, N.; Weinberg, M. D.

We use a large sample of galaxies from the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to explore the distribution of galaxy luminosities, stellar and baryonic masses, and sizes in the local Universe. Assuming a universally-applicable stellar IMF, highlights include the following. i) The 'faint end slope' of the stellar mass function is steeper than -1.1, steeper than many recent estimates. ii) Between 1/2 and 3/4 of present-day stellar mass is in early-type galaxies. iii) Only 8 ± 4% of baryons are in stars or cold gas (< 104K) in galaxies, arguing for an overall low galaxy formation efficiency. iv) The width of the galaxy scale size distribution depends on passband, in the sense that the optical scale size distributions are narrower than those in the near-infrared.

Basically you are indulging in the fantasy that the mass in stars has been underestimated by a factor of 25 (2500%!), and of course that all of the mass is in the stars, e.g. the ICM (which has been measured to exist) does not exist!

 

[Reality Check]

Ya, including ordinary matter. I've yet to hear you folks address that "dust" in space revelation from a few years ago, or that revelation that galaxies are twice as bright as first thought, or that "stellar recount" data that that shows that small stars were underestimated by a factor of FOUR!

I will point out that your memory is abysmal.
You posted links to the 3 news articles on 21st May 2011 in this thread.
The comprehensive answer to the papers was posted by Tim Thompson on 21st May 2011: Science by Press Release Loses Again

...
All 3 of Mozina's links constitute no problem for dark matter cosmology, either individually or all together. As has been said many times, you can't do science by press release, or news reports. Mozina does not try to see beyond the press release, and so gets the science all wrong, seriously overestimating the effect on dark matter cosmology.

You have known since at last 21st May 2011 that these papers at most produce a small change in the visible mass of stars. It still leaves ~95% of the universe as invisble mass or energy.

ETA: We could go back to my reply on 21st August 2009 on one of the papers:

You misread the article.
The point is that these stars are not "highly visible" and so their numbers were estimated in the past. Current observation techniques have revealed that in some galaxies the smaller mass stars may be miscounted by a factor of 4.

They do have a "good handle" on the mass of the baryonic material in a galaxy. This new observation will allow more accurate estimates of galaxy masses.
A real astronomer could tell us the real error limit in galaxy mass calculations (50%?)

ETA: The actual journal article looks like "Evidence for a Nonuniform Initial Mass Function in the Local Universe".

 

[Michael Mozina]

Nope. That observation makes it impossible.

I assume you're referring to this paper: http://iopscience.iop.org/1538-4357/678/2/L101/pdf/1538-4357_678_2_L101.pdf

Look at Fig. 4. The orange line is the observed luminosity of stars as a function of wavelength. The black line is the true (i.e. before being absorbed by dust) luminosity according to their model. Notice how they coincide almost perfectly once you get 2 micrometers or so? That's because dust hardly absorbs starlight at all at those longer wavelengths. But your proposal would double the luminosity at all wavelengths, which is not at all consistent with observation.

FYI, thanks for that explanation. At least I now understand WHY you're choosing one option over another. You'll have to let me chew on that a bit before I respond any further. I'm not sure I agree that's why they come into alignment, but at least I understand your argument (finally). Thanks for that.

 

[Michael Mozina]

Look at Fig. 4. The orange line is the observed luminosity of stars as a function of wavelength. The black line is the true (i.e. before being absorbed by dust) luminosity according to their model. Notice how they coincide almost perfectly once you get 2 micrometers or so?

FYI, It's not clear to me yet that the lines actually coincide or if Baldry & Glazebrook's data set (orange) simply ends at that point the orange line terminates. Are you sure that their calculated data site goes beyond the 2 micrometer range?

 

[sol invictus]

FYI, It's not clear to me yet that the lines actually coincide or if Baldry & Glazebrook's data set (orange) simply ends at that point the orange line terminates. Are you sure that their calculated data site goes beyond the 2 micrometer range?

They mention 2.1 micrometer starlight in the abstract. Only a small fraction (13%+-3) is absorbed by dust, according to their model.

 

[Michael Mozina]

They mention 2.1 micrometer starlight in the abstract. Only a small fraction (13%+-3) is absorbed by dust, according to their model.

Based on the rest of the wavelengths in the graph and the limitations of the data, I'm having a hard time buying the argument. I suppose I'll have to spend some more time on it this afternoon. At least I think I understand your preference for one method of resolving the brightness problem over the other now and that was helpful. Thank you.

I'm not sure that I agree with your preference of one idea over the other mind you, but it's helpful to to at least understand the argument.

 

[Wangler]

They mention 2.1 micrometer starlight in the abstract. Only a small fraction (13%+-3) is absorbed by dust, according to their model.

Isn't that also where they stop their analysis, at the 2.1 µm (K-band) point? Regardless, a simple straight line extrapolation on Figure 3 shows that the escape fraction is 100% by the time you get to 3 µm.

How would the luminosity increase relate to stellar mass? While there clearly aren't twice the number of stars, how many more stars (and of what type and mass) would there have to be to almost double the energy output from 0.9x10³⁵ to 1.6x10³⁵ W Mpc^-1 as stated in the paper?

If we are trying to make up an energy gap at the shorter wavelengths, perhaps we have more bluer stars?

Perhaps we have fewer red stars than we think, and more bluer stars?

 

[sol invictus]

Perhaps we have fewer red stars than we think, and more bluer stars?

(Let me preface this by saying that I have not read the relevant papers carefully, nor am I particular knowledgeable on stellar astrophysics. So I may be pretty far off on something.)

I don't think there can be fewer red stars, but it does seem that they are proposing to increase the number of blue stars.

Looking here, it seems that more massive stars are both bluer and much more luminous. For example, stars with twice the mass of the sun are 25 times as luminous, and significantly bluer. Stars 16 times the mass of the sun are 30,000 times as luminous.

That shows that doubling the luminosity might only require a fairly minor increase in total mass. For instance, if for every 30,000 solar mass stars you added a single 16 solar mass star, you'd have doubled the luminosity of that population of stars, but only increased its total mass by 16/30,000 = .05%.

 

[Wangler]

Looking here, it seems that more massive stars are both bluer and much more luminous. For example, stars with twice the mass of the sun are 25 times as luminous, and significantly bluer. Stars 16 times the mass of the sun are 30,000 times as luminous.

That shows that doubling the luminosity might only require a fairly minor increase in total mass. For instance, if for every 30,000 solar mass stars you added a single 16 solar mass star, you'd have doubled the luminosity of that population of stars, but only increased its total mass by 16/30,000 = .05%.

In the paper (Figure 4), there are two peaks in the left side grey area, one at about 0.1 µm, the other at about 0.8 µm, corresponding to temperatures of ~29,000K and 3600K, respectively.

Looking at that nice spectral classification chart you linked, we are looking at stars with masses of 2.1 to 16 M_o and at least 25,000 times solar luminosity for the higher temp, and 0.45 M_o with 0.08 L_o at the lower temp.

For lots of additional mass, those Class M stars pack a lot of punch per unit of luminosity, but they also contribute a lot of energy at the wavelengths above at which point the shaded area disappears. So it seems like there can't be too many more red stars.

For the blue stars (Class B), the energy in their black body spectra is very close to zero when you get to the 2.1 µm point at which the energy surplus goes to zero (the grey disappears).

My simplistic analysis seems to agree with you Sol; there are a few more blue stars which contribute large amounts of energy but little mass, but not that many more red stars.

 

[Tim Thompson]

Stars and Baryonic Dark Matter IV

Isn't that also where they stop their analysis, at the 2.1 µm (K-band) point? Regardless, a simple straight line extrapolation on Figure 3 shows that the escape fraction is 100% by the time you get to 3 µm.

Dust opacity drops pretty sharply by 3 µm and beyond, but so does stellar emission. Dust opacity becomes large again around 10 µm because of silicate absorption features, and after that the opacity is a strong function of both wavelength and dust particle size (see, e.g., Optical Properties of Dust Grains in the Infrared: Our View on Cosmic Dust, M. Min; ASP Conference on "Cosmic Dust - Near and Far", 8-12 Sep 2008, published December 2009).

I worked with IRAC images out of the Spitzer Space Telescope, which has channels at 3.6 µm, 4.5 µm, 5.8 µm & 8.0 µm. The 3.6 µm channel is dominated by starlight, but stars are very weak at 4.5 µm and essentially invisible at 5.8 µm & 8.0 µm, and that's not due to dust opacity, it's due to the fact that there is essentially no starlight at wavelengths that long. But to get an idea of dust opacity that you can see, compare these two images:

1. Axel Mellinger's Milky Way Panorama 2.0
2. 2MASS Showcase: The Infrared Milky Way

Mellinger's panorama is a mosaic of about 3000 individual CCD images that is balanced for color & relative brightness to the human eye, which is most sensitive to light wavelengths where solar class stars are brightest, about 0.55 µm. In this image you can clearly see how well the dust concentrated along the plane of the Milky Way obscures the stars behind it.

The 2MASS ("2 Micron All Sky Survey") image is a composite all sky image where eyeball RGB corresponds to wavelengths in the infrared as 1.2 µm (blue), 1.6 µm (green) & 2.2 µm (red). The all sky orientation is the same as in Mellinger's image, so you can see & compare the same features in both images. The 2MASS image is all starlight & dust. As you can see, far more starlight is visible in the plane of the Milky Way in the 2MASS image than is the case in Mellinger's image.

In this case, the difference is due to far lower dust opacity at the infrared wavelengths. Starlight is far dimmer at the long 2MASS wavelengths, but the dust opacity is far lower than in visible wavelengths, and far more starlight directly escapes the galaxy at longer wavelengths. That's why Driver, et al., are not specific about how they model starlight beyond 2.1 µm, there simply is not enough of it left anymore to bother their cosmological starlight in any significant way.

How would the luminosity increase relate to stellar mass?

But just looking at the standard main sequence mass (M) - luminosity (L) relationship (L = M^3.5) I would guess that increasing the brightness by a factor of 2 would increase the implied mass by a smaller factor, about 1.2 (i.e., new stellar mass estimate = 1.2 x old stellar mass estimate).

The mass luminosity relationship for main sequence stars is extremely well established. The relationship is between the luminosity and the mass of the stars, not the number of stars. If I double L to 2L then I have to increase M by 1.2 so that M^3.5 will also double to 2(M^3.5) (a little diddling shows that a more precise number is 1.21903, close enough to 1.2 for the purpose of this discussion).

If you are talking in simple, general terms about mass & luminosity, that's it.

Looking here, it seems that more massive stars are both bluer and much more luminous. For example, stars with twice the mass of the sun are 25 times as luminous, and significantly bluer. Stars 16 times the mass of the sun are 30,000 times as luminous.

This is important in light of this ...

If the galaxies are twice as bright, you could just as easily double the number of large stars in a galaxy.

This is one of the points I was criticizing. If we are specific about the wavelength dependence of the apparent brightness, then we must be equally specific about the class of stars were are going to increase because of the strong effect mass has on the wavelengths of peak brightness for stellar classes. Increase the number of small red stars and you increase the number of long wavelength photons, whereas if you increase large high mass stars you really pump up the short wavelength ultraviolet (UV) photons big time. In the absence of any claim that there is too much UV emission, you just can't diddle the high mass stars like that. Furthermore, the direct empirical relationship we have to work with is between stellar luminosity and stellar mass, not stellar number counts. Stick with what you know and you can't go too far wrong. That's why I stick to the well known mass-luminosity relationship as a guide, and that's why I concentrate on lower mass stars, because I know there is no UV emission to justify the addition of high mass stars.

I will have more to say later but I have a chess tournament to get ready for now.

 

[Wangler]

That's why I stick to the well known mass-luminosity relationship as a guide, and that's why I concentrate on lower mass stars, because I know there is no UV emission to justify the addition of high mass stars.

But in the Driver, et. al. paper, they show a lot of the energy excess in the UV band.

 

[Michael Mozina]

But in the Driver, et. al. paper, they show a lot of the energy excess in the UV band.

 

[Wangler]

Remember, the higher mass stars each contribute whole bunches of luminosity, while changing the aggregate mass very much. At least, if I understand things correctly.

The lower mass stars give more unit mass per unit luminosity, but unfortunately the energy output of the lower mass stars is towards the longer wavelengths, where Driver, et. al. demonstrate there is not much if any missing energy.