# Thread: Simple 'Universal' DM 'halo' calculations

1. LaurieAG,

2. Originally Posted by Shaula
It also uses dark matter. It is about missing baryons, not dark matter. Do the math - it has a universe made of 69% dark energy, 5% baryonic matter. What's missing? It explicitly states several times that it uses the Planck15 cosmology.
The paper uses DM for 'dispersion measures' and there is only one reference to dark matter 'These models approximate halos as retaining their gas in a manner that traces the dark matter above some mass threshold' to 'span the likely range of possible feedback scenarios'. They studiously avoid the use of the term 'dark matter' and instead use matter and dark energy in the paper.

More than three quarters of the baryonic content of the Universe resides in a highly diffuse state that is difficult to observe, with only a small fraction directly observed in galaxies and galaxy clusters. Censuses of the nearby Universe have used absorption line spectroscopy to observe these invisible baryons, but these measurements rely on large and uncertain corrections and are insensitive to the majority of the volume, and likely mass.

3. https://forum.cosmoquest.org/showthr...97#post2513697
https://forum.cosmoquest.org/showthr...36#post2513536

HD 140283 is 190LY away from us and, according to Wikipedia, the Milky way radius is approximately 100kLY for the baryonic matter and approximately 1,000kLY for the dM halo radius. Observations of max reddening of something at the other side of our galaxy would require 1/500 of the reddening (to HD 140283) to get max while observing a star at a similar distance in the halo would require 1/5000 of the reddening (to HD 140283) to get max. I checked your post and note you did not put the 'reddening' text within a quote.

Originally Posted by Reality Check
The missing baryon problem was that we had only detected half of the 4.85% of the universe that is the baryons of visible matter. This was resolved in 2017 by finding more intergalactic matter from the Sunyaev-Zel'dovich effect. The irrelevant to this thread A census of baryons in the Universe from localized fast radio bursts paper is a way of directly detecting the baryons.
We seem to have an excess of baryons if only half were missing. From the paper.

More than three quarters of the baryonic content of the Universe resides in a highly diffuse state that is difficult to observe, with only a small fraction directly observed in galaxies and galaxy clusters. Censuses of the nearby Universe have used absorption line spectroscopy to observe these invisible baryons, but these measurements rely on large and uncertain corrections and are insensitive to the majority of the volume, and likely mass.

4. Order of Kilopi
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Originally Posted by LaurieAG
The paper uses DM for 'dispersion measures' and there is only one reference to dark matter 'These models approximate halos as retaining their gas in a manner that traces the dark matter above some mass threshold' to 'span the likely range of possible feedback scenarios'. They studiously avoid the use of the term 'dark matter' and instead use matter and dark energy in the paper.
I know what they use DM for in the paper. I also know that they use the Planck15 cosmology, as they say several times, and that they have a universe of 5% baryonic matter and 69% dark energy. So the rest must be .... Well, not dark energy and not baryonic matter. And not something that interacts electromagnetically as that would affect the dispersion measure. And something that is part of the Planck15 cosmology. I wonder what that remaining stuff could be? Gosh, so many candidates.

The paper doesn't support your nebulous, untestable ideas that solve no problems and answer no questions. This is a pointless discussion as it is not relevant to your original post. Even if you could show that this paper doesn't use dark matter (it does) that would not advance anything you have claimed. As I said before - you've consistently dodged most questions put to you and replied much as you have above. A series of sometimes correct but usually irrelevant statements.

5. Order of Kilopi
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Originally Posted by LaurieAG
HD 140283 is 190LY away from us ....
An irrelevant post about HD 140283 and reddening of light from stars on the far side of the Milky Way.

Then a "We seem to have an excess of baryons" fantasy and an irrelevant quote that does not state that more than half of the baryons were missing. It is the statement that 3/4 ths of the mass in the universe is not in galaxies and galaxy clusters. It is the statement that trying to detect the gas between galaxies and galaxy clusters using absorption line spectroscopy does not detect that mass.
Read the source that was cited, LaurieAG: Missing baryon problem
The missing baryon problem was a problem related to the fact that the observed amount of baryonic matter did not match theoretical predictions. The density of baryons can be constrained according to Big Bang nucleosynthesis and the cosmic microwave background. Observations by the Planck spacecraft in 2015, yielded a theoretical value for baryonic matter of 4.85% of the contents of the Universe.[1] However, directly adding up all the known baryonic matter produces a baryonic density slightly less than half of this.[2] The missing baryon problem is distinct from the dark matter problem, which is mainly non-baryonic in nature.[3]
The resolution is "hot strands between galaxy pairs" and their density is "the exact amount needed to solve the problem". That detection used the Sunyaev–Zeldovich effect, thus no issues with absorption line spectroscopy.

6. I'd like to thank everybody who has contributed and, as I can't please everybody (this is ATM after all), this will be my final post in this thread.

I use the simple halo model presented in the OP to get a better understanding of the ΛCDM model ratios and the Virial theorem as used in galaxies for comparison purposes and to gain insights into how these mechanisms work.

The OP model is scaled on the basis of dark matter having the same density of baryonic matter and the resulting radii are calculated on this basis. In the Milky Way, according to the figures from Wikipedia, the dark matter halo radius is 10 times the baryonic matter radius so the total galaxy volume is 1000 times larger (10^3 vs 1^3) than the baryonic volume and the average density of the dark matter component is roughly 1/200th (≈ 5/1000) or 0.5% of the baryonic matter component for equal volumes.

It seems obvious that Δc, the critical overdensity constant, used in the Virial theorem for galaxies is a multiple (i.e. 200) appled to the dark matter density to match the current baryonic density and get the ratios determined by ΛCDM. On this same basis the dark matter density in ΛCDM should be roughly 1/100 (≈ 5/500) or 1.0% of the baryonic matter density with a calculated overdensity constant of ≈ 100 with the same ratio between the dark matter component and the baryonic matter component. With respect to the universal halo model presented in the OP, the dark matter radius should be 7.94 based on the Δc from the ΛCDM model or 10 for the Milky Way virial model.

The only difference between the ΛCDM model (at the CMB) and the Milky Way virial model (NOW), as shown in a simple halo model based on a constant ratio of the dark matter component to the baryonic matter component, is the volume of the dark matter component doubles while its density halves over the intervening period.

A simplification of the ΛCDM model ratios is contained in the image below. This can be used as a guide to see if results are compliant with the ΛCDM model regardless of the density.

7. Thread closed per OP's stated intent to cease participating.

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