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The dark matter crisis
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jacob navia
Apr 24, 2012, 2:10:19 PM4/24/12
to
Contrary to what I believed, the article of ESO that I pointed out last
week is by far not the only serious article that cast doubts in the very
existence of dark matter.
Another astronomer took a volume of 50Mpc around our galaxy, added all
the masses of galaxies in that volume and obtained that... well, dark
matter is missing. See:
http://arxiv.org/abs/1204.3377
Missing Dark Matter in the Local Universe
So, dark matter is not only missing near the sun, but it is also missing
near our galaxy. All evidence points to the same direction:
Dark matter doesn't exist.
I have this data from a very interesting blog entry:
http://www.scilogs.eu/en/blog/the-dark-matter-crisis
jacob
week is by far not the only serious article that cast doubts in the very
existence of dark matter.
Another astronomer took a volume of 50Mpc around our galaxy, added all
the masses of galaxies in that volume and obtained that... well, dark
matter is missing. See:
http://arxiv.org/abs/1204.3377
Missing Dark Matter in the Local Universe
So, dark matter is not only missing near the sun, but it is also missing
near our galaxy. All evidence points to the same direction:
Dark matter doesn't exist.
I have this data from a very interesting blog entry:
http://www.scilogs.eu/en/blog/the-dark-matter-crisis
jacob
Phillip Helbig---undress to reply
Apr 25, 2012, 2:37:55 AM4/25/12
to
In article <mt2.0-400-...@hydra.herts.ac.uk>, jacob navia
The average density of matter in this volume, Omega_m,loc=0.08+-0.02,
turns out to be much lower than the global cosmic density Omega_m,
glob=0.28+-0.03.
It has been known for a long time that the apparent value of Omega
increases with scale up to about 0.3 or so. Basically, any dynamical
test cannot detect mass which is smooth on a scale larger than that
examined. However, even Omega=0.08 implies non-baryonic dark matter.
We discuss three possible explanations of this paradox: 1) galaxy
groups and clusters are surrounded by extended dark halos, the major
part of the mass of which is located outside their virial radii; 2)
the considered local volume of the Universe is not representative,
being situated inside a giant void; and 3) the bulk of matter in the
Universe is not related to clusters and groups, but is rather
distributed between them in the form of massive dark clumps. Some
arguments in favor of the latter assumption are presented.
Note that ALL THREE of these possible explanations do not reject the
idea of dark matter.
<ja...@spamsink.net> writes:
> Contrary to what I believed, the article of ESO that I pointed out last
> week is by far not the only serious article that cast doubts in the very
> existence of dark matter.
>
> Another astronomer took a volume of 50Mpc around our galaxy, added all
> the masses of galaxies in that volume and obtained that... well, dark
> matter is missing. See:
>
> http://arxiv.org/abs/1204.3377
> Missing Dark Matter in the Local Universe
Quoting from the abstract:
> Contrary to what I believed, the article of ESO that I pointed out last
> week is by far not the only serious article that cast doubts in the very
> existence of dark matter.
>
> Another astronomer took a volume of 50Mpc around our galaxy, added all
> the masses of galaxies in that volume and obtained that... well, dark
> matter is missing. See:
>
> http://arxiv.org/abs/1204.3377
> Missing Dark Matter in the Local Universe
The average density of matter in this volume, Omega_m,loc=0.08+-0.02,
turns out to be much lower than the global cosmic density Omega_m,
glob=0.28+-0.03.
It has been known for a long time that the apparent value of Omega
increases with scale up to about 0.3 or so. Basically, any dynamical
test cannot detect mass which is smooth on a scale larger than that
examined. However, even Omega=0.08 implies non-baryonic dark matter.
We discuss three possible explanations of this paradox: 1) galaxy
groups and clusters are surrounded by extended dark halos, the major
part of the mass of which is located outside their virial radii; 2)
the considered local volume of the Universe is not representative,
being situated inside a giant void; and 3) the bulk of matter in the
Universe is not related to clusters and groups, but is rather
distributed between them in the form of massive dark clumps. Some
arguments in favor of the latter assumption are presented.
Note that ALL THREE of these possible explanations do not reject the
idea of dark matter.
jacob navia
Apr 25, 2012, 5:56:33 AM4/25/12
to
Le 25/04/12 08:37, Phillip Helbig---undress to reply a écrit :
<quote>
The idea is as simple as it is brilliant: cosmology has precise
predictions as to what is the content of our universe. In particular, it
predicts the density of matter to be Ωm,glob = 0.28 +- 0.03 (83 per cent
of this in dark, 17 per cent in luminous matter). Now, to test this, all
you have to do is to sum up all the mass within a certain volume of
space, and you can estimate the actual density of mass within that
volume. To be sure that your volume is representative, it needs to be
large. If you only sum over, say, a sphere of 100 kpc in diameter, the
density strongly depends on whether you have a galaxy in this volume or
not. Karachentsev chose to use a volume of 50 Mpc around the MW. On this
size-scale, the density is expected to fluctuate by only 10 percent, a
reasonably low value in astronomy. The scale can thus be assumed to be
representative and you should observe the mass density predicted by LCDM.
Except that you do not.
Karachentsev reports that the average mass density is only Ωm,loc = 0.08
+- 0.02, a factor of 3-4 lower than predicted and can not be explained
by the uncertainties in the data or prediction. As most of the
mass-content in the Universe is supposed to be dark matter, this means
that most dark matter is missing in this volume.
<end quote>
> We discuss three possible explanations of this paradox: 1) galaxy
> groups and clusters are surrounded by extended dark halos, the major
> part of the mass of which is located outside their virial radii; 2)
> the considered local volume of the Universe is not representative,
> being situated inside a giant void; and 3) the bulk of matter in the
> Universe is not related to clusters and groups, but is rather
> distributed between them in the form of massive dark clumps. Some
> arguments in favor of the latter assumption are presented.
>
> Note that ALL THREE of these possible explanations do not reject the
> idea of dark matter.
Yes, but that leads to further problems, as they explain in that blog:
<quote>
It is not straight-forward to interpret this result, except that it
might be a serious problem for LCDM. In the paper three solutions within
the framework of standard dark matter cosmology are suggested. First of
all, we might resort to the unsatisfying claim that the local Universe
is exceptionally non-representative of the Universe as a whole. We would
then sit in a local void, a very large under-dense region of the
Universe. Unfortunately, as Karachentsev states in his paper, this is in
contradiction to observations. The other two suggested solutions are
based on the idea that maybe not all mass is counted. Dark matter is
defined to be an elusive thing, after all. Dark halos might be more
extended than predicted in the models, pushing it outside the virial
radius of a halo, the region in which observations can indirectly
'measure' it from the dynamics. However, taking this as a solution to
the observed mass-deficit 'clearly contradicts the existing
observational data', as Karachentsev states in his work. But maybe much
of the dark matter is hiding somewhere else? Karachentsev suggests it to
be in massive dark clumps not filled with galaxies (he calls them 'dark
attractors'), and thus is invisible to us when looking for galaxies
only. But how could these dark clumps, with masses of galaxy-clusters,
remain dark? You would need to separate the baryonic, luminous matter
from a large bunch of dark matter to make sure no galaxies from in the
dark attractor.
In any case, these suggestions require modifications to the behavior of
dark matter because their processes are not predicted in current models.
None of these possibilities seem very attractive, leaving us with the
conclusion that, assuming we live in a LCDM universe, a large fraction
of the dark matter is gone missing.
> In article<mt2.0-400-...@hydra.herts.ac.uk>, jacob navia
> <ja...@spamsink.net> writes:
>
>> Contrary to what I believed, the article of ESO that I pointed out last
>> week is by far not the only serious article that cast doubts in the very
>> existence of dark matter.
>>
>> Another astronomer took a volume of 50Mpc around our galaxy, added all
>> the masses of galaxies in that volume and obtained that... well, dark
>> matter is missing. See:
>>
>> http://arxiv.org/abs/1204.3377
>> Missing Dark Matter in the Local Universe
>
> Quoting from the abstract:
>
> The average density of matter in this volume, Omega_m,loc=0.08+-0.02,
> turns out to be much lower than the global cosmic density Omega_m,
> glob=0.28+-0.03.
>
> It has been known for a long time that the apparent value of Omega
> increases with scale up to about 0.3 or so. Basically, any dynamical
> test cannot detect mass which is smooth on a scale larger than that
> examined. However, even Omega=0.08 implies non-baryonic dark matter.
>
Look, that is discussed in the cited blog entry. They say:
> <ja...@spamsink.net> writes:
>
>> Contrary to what I believed, the article of ESO that I pointed out last
>> week is by far not the only serious article that cast doubts in the very
>> existence of dark matter.
>>
>> Another astronomer took a volume of 50Mpc around our galaxy, added all
>> the masses of galaxies in that volume and obtained that... well, dark
>> matter is missing. See:
>>
>> http://arxiv.org/abs/1204.3377
>> Missing Dark Matter in the Local Universe
>
> Quoting from the abstract:
>
> The average density of matter in this volume, Omega_m,loc=0.08+-0.02,
> turns out to be much lower than the global cosmic density Omega_m,
> glob=0.28+-0.03.
>
> It has been known for a long time that the apparent value of Omega
> increases with scale up to about 0.3 or so. Basically, any dynamical
> test cannot detect mass which is smooth on a scale larger than that
> examined. However, even Omega=0.08 implies non-baryonic dark matter.
>
<quote>
The idea is as simple as it is brilliant: cosmology has precise
predictions as to what is the content of our universe. In particular, it
predicts the density of matter to be Ωm,glob = 0.28 +- 0.03 (83 per cent
of this in dark, 17 per cent in luminous matter). Now, to test this, all
you have to do is to sum up all the mass within a certain volume of
space, and you can estimate the actual density of mass within that
volume. To be sure that your volume is representative, it needs to be
large. If you only sum over, say, a sphere of 100 kpc in diameter, the
density strongly depends on whether you have a galaxy in this volume or
not. Karachentsev chose to use a volume of 50 Mpc around the MW. On this
size-scale, the density is expected to fluctuate by only 10 percent, a
reasonably low value in astronomy. The scale can thus be assumed to be
representative and you should observe the mass density predicted by LCDM.
Except that you do not.
Karachentsev reports that the average mass density is only Ωm,loc = 0.08
+- 0.02, a factor of 3-4 lower than predicted and can not be explained
by the uncertainties in the data or prediction. As most of the
mass-content in the Universe is supposed to be dark matter, this means
that most dark matter is missing in this volume.
<end quote>
> We discuss three possible explanations of this paradox: 1) galaxy
> groups and clusters are surrounded by extended dark halos, the major
> part of the mass of which is located outside their virial radii; 2)
> the considered local volume of the Universe is not representative,
> being situated inside a giant void; and 3) the bulk of matter in the
> Universe is not related to clusters and groups, but is rather
> distributed between them in the form of massive dark clumps. Some
> arguments in favor of the latter assumption are presented.
>
> Note that ALL THREE of these possible explanations do not reject the
> idea of dark matter.
<quote>
It is not straight-forward to interpret this result, except that it
might be a serious problem for LCDM. In the paper three solutions within
the framework of standard dark matter cosmology are suggested. First of
all, we might resort to the unsatisfying claim that the local Universe
is exceptionally non-representative of the Universe as a whole. We would
then sit in a local void, a very large under-dense region of the
Universe. Unfortunately, as Karachentsev states in his paper, this is in
contradiction to observations. The other two suggested solutions are
based on the idea that maybe not all mass is counted. Dark matter is
defined to be an elusive thing, after all. Dark halos might be more
extended than predicted in the models, pushing it outside the virial
radius of a halo, the region in which observations can indirectly
'measure' it from the dynamics. However, taking this as a solution to
the observed mass-deficit 'clearly contradicts the existing
observational data', as Karachentsev states in his work. But maybe much
of the dark matter is hiding somewhere else? Karachentsev suggests it to
be in massive dark clumps not filled with galaxies (he calls them 'dark
attractors'), and thus is invisible to us when looking for galaxies
only. But how could these dark clumps, with masses of galaxy-clusters,
remain dark? You would need to separate the baryonic, luminous matter
from a large bunch of dark matter to make sure no galaxies from in the
dark attractor.
In any case, these suggestions require modifications to the behavior of
dark matter because their processes are not predicted in current models.
None of these possibilities seem very attractive, leaving us with the
conclusion that, assuming we live in a LCDM universe, a large fraction
of the dark matter is gone missing.
Phillip Helbig---undress to reply
Apr 26, 2012, 4:33:45 AM4/26/12
to
In article <mt2.0-29923...@hydra.herts.ac.uk>, jacob navia
have to estimate it by its dynamical effects. However, these are
produced by gradients in mass distributions. Any dark matter smoothly
distributed on the scale surveyed is not detectable by dynamical
methods.
Actually, the idea of dark matter arose because when one "sums up all
the mass" of visible matter, one needs more matter to explain dynamic
effects (e.g. flat rotation curves of galaxies). So, this is not a new
idea. WE DON'T KNOW WHAT THE DARK MATTER IS. Assuming that the
cosmological value of 0.28 is correct, we don't know at what scale
that is reached.
> To be sure that your volume is representative, it needs to be
> large. If you only sum over, say, a sphere of 100 kpc in diameter, the
> density strongly depends on whether you have a galaxy in this volume or
> not. Karachentsev chose to use a volume of 50 Mpc around the MW. On this
> size-scale, the density is expected to fluctuate by only 10 percent, a
> reasonably low value in astronomy. The scale can thus be assumed to be
> representative and you should observe the mass density predicted by LCDM.
But if one doesn't know what the dark matter is, how secure is the
assumption that it is expected to fluctuate by only 10 percent?
> Dark halos might be more
> extended than predicted in the models, pushing it outside the virial
> radius of a halo, the region in which observations can indirectly
> 'measure' it from the dynamics. However, taking this as a solution to
> the observed mass-deficit 'clearly contradicts the existing
> observational data', as Karachentsev states in his work.
His conclusion also contradicts other observational data. By this
logic, he should rule out his own conclusion. As he notes, dark haloes
might be more extended than in the MODELS. No-one knows the actual
distribution.
> But maybe much
> of the dark matter is hiding somewhere else? Karachentsev suggests it to
> be in massive dark clumps not filled with galaxies (he calls them 'dark
> attractors'), and thus is invisible to us when looking for galaxies
> only. But how could these dark clumps, with masses of galaxy-clusters,
> remain dark?
Why do they have the masses of galaxy clusters? All he can conclude is
that they must contain some total mass. Where does the assumption come
from that the concentrations have the mass of galaxy clusters?
> You would need to separate the baryonic, luminous matter
> from a large bunch of dark matter to make sure no galaxies from in the
> dark attractor.
This is an old idea, known as biased galaxy formation. He makes it
sound like something strange. The idea is that baryonic matter collects
in the larger concentrations of dark matter, leading to an enrichment
there. This is perfectly plausible.
> In any case, these suggestions require modifications to the behavior of
> dark matter because their processes are not predicted in current models.
Again, no-one knows what the dark matter is. Maybe some hypotheses,
models, are ruled out, but not the whole idea.
> None of these possibilities seem very attractive,
Why not?
<ja...@spamsink.net> writes:
> The idea is as simple as it is brilliant: cosmology has precise
> predictions as to what is the content of our universe. In particular, it
> predicts the density of matter to be Ωm,glob = 0.28 +- 0.03 (83 per cent
> of this in dark, 17 per cent in luminous matter). Now, to test this, all
> you have to do is to sum up all the mass within a certain volume of
> space, and you can estimate the actual density of mass within that
> volume.
Right, but how do you "sum up all the mass"? If you can't see it, you
> The idea is as simple as it is brilliant: cosmology has precise
> predictions as to what is the content of our universe. In particular, it
> predicts the density of matter to be Ωm,glob = 0.28 +- 0.03 (83 per cent
> of this in dark, 17 per cent in luminous matter). Now, to test this, all
> you have to do is to sum up all the mass within a certain volume of
> space, and you can estimate the actual density of mass within that
> volume.
have to estimate it by its dynamical effects. However, these are
produced by gradients in mass distributions. Any dark matter smoothly
distributed on the scale surveyed is not detectable by dynamical
methods.
Actually, the idea of dark matter arose because when one "sums up all
the mass" of visible matter, one needs more matter to explain dynamic
effects (e.g. flat rotation curves of galaxies). So, this is not a new
idea. WE DON'T KNOW WHAT THE DARK MATTER IS. Assuming that the
cosmological value of 0.28 is correct, we don't know at what scale
that is reached.
> To be sure that your volume is representative, it needs to be
> large. If you only sum over, say, a sphere of 100 kpc in diameter, the
> density strongly depends on whether you have a galaxy in this volume or
> not. Karachentsev chose to use a volume of 50 Mpc around the MW. On this
> size-scale, the density is expected to fluctuate by only 10 percent, a
> reasonably low value in astronomy. The scale can thus be assumed to be
> representative and you should observe the mass density predicted by LCDM.
assumption that it is expected to fluctuate by only 10 percent?
> Dark halos might be more
> extended than predicted in the models, pushing it outside the virial
> radius of a halo, the region in which observations can indirectly
> 'measure' it from the dynamics. However, taking this as a solution to
> the observed mass-deficit 'clearly contradicts the existing
> observational data', as Karachentsev states in his work.
logic, he should rule out his own conclusion. As he notes, dark haloes
might be more extended than in the MODELS. No-one knows the actual
distribution.
> But maybe much
> of the dark matter is hiding somewhere else? Karachentsev suggests it to
> be in massive dark clumps not filled with galaxies (he calls them 'dark
> attractors'), and thus is invisible to us when looking for galaxies
> only. But how could these dark clumps, with masses of galaxy-clusters,
> remain dark?
that they must contain some total mass. Where does the assumption come
from that the concentrations have the mass of galaxy clusters?
> You would need to separate the baryonic, luminous matter
> from a large bunch of dark matter to make sure no galaxies from in the
> dark attractor.
sound like something strange. The idea is that baryonic matter collects
in the larger concentrations of dark matter, leading to an enrichment
there. This is perfectly plausible.
> In any case, these suggestions require modifications to the behavior of
> dark matter because their processes are not predicted in current models.
models, are ruled out, but not the whole idea.
> None of these possibilities seem very attractive,
eric gisse
Apr 26, 2012, 7:10:24 AM4/26/12
to
jacob navia <ja...@spamsink.net> wrote in
news:mt2.0-29923...@hydra.herts.ac.uk:
[...]
Expected by whom?
http://www.deus-consortium.org/wp-
content/uploads/2012/03/fur_halos_web1.jpg
The relevant part of the picture is on the right.
It'd probably be reasonably interesting to repeat this kind of calculation
around several different points to see what actual level of fluctuations
are seen.
[snip rest of blog copypaste]
news:mt2.0-29923...@hydra.herts.ac.uk:
[...]
> Karachentsev chose to use a
> volume of 50 Mpc around the MW. On this size-scale, the density is
> expected to fluctuate by only 10 percent
[...]
> volume of 50 Mpc around the MW. On this size-scale, the density is
> expected to fluctuate by only 10 percent
Expected by whom?
http://www.deus-consortium.org/wp-
content/uploads/2012/03/fur_halos_web1.jpg
The relevant part of the picture is on the right.
It'd probably be reasonably interesting to repeat this kind of calculation
around several different points to see what actual level of fluctuations
are seen.
[snip rest of blog copypaste]
eric gisse
Apr 26, 2012, 7:11:18 AM4/26/12
to
jacob navia <ja...@spamsink.net> wrote in
news:mt2.0-400-...@hydra.herts.ac.uk:
> Contrary to what I believed, the article of ESO that I pointed out
> last week is by far not the only serious article that cast doubts in
> the very existence of dark matter.
we believe dark matter exists.
You seem to have missed the resultant technical discussion as well.
>
> Another astronomer took a volume of 50Mpc around our galaxy, added all
> the masses of galaxies in that volume and obtained that... well, dark
> matter is missing. See:
>
> http://arxiv.org/abs/1204.3377
> Missing Dark Matter in the Local Universe
>
> So, dark matter is not only missing near the sun, but it is also
> missing near our galaxy. All evidence points to the same direction:
>
> Dark matter doesn't exist.
several kiloparsecs wide in a location that is nearly FIVE THOUSAND
LIGHTYEARS above our current position in the galactic disk.
As far as that article is concerned...I have an extremely large volume
of skepticism regarding the result.
Lets take the result at face value first, that the local matter density
is a factor of 3 or so smaller than the global value. Why is that a
problem?
The universe is already known to be inhomogeneus and we have repeatedly
seen that there are spots (the great void for example) in the universe
quite a bit bigger than the locally surveyed volume which have even less
"stuff".
Repeating this observation within the void would get what result do you
imagine?
Plus there's the fact that this paper cited other observations that
_are_ consistent with the global value, which leads me to think there is
a nontrivial volume of systematic errors in the observation. Which
really should be a surprise to nobody if the notion is considered.
Now lets look at the actual methodology...
The most basic notion seems to be that if we count the galaxies, obtain
their luminosities, account for clustering, and abuse the Tully-Fisher
relation we can get an estimate of the local mass density. Emphasis on
"local" - a region 150 million light years wide isn't that big in the
scheme of things.
I see a few problems with this.
1) The method is akin to us surveying the local solar system to
determine the density of matter in the galaxy, or just the local
stellar neighborhood. Its' poor sampling no matter how you spin it.
2) Dark energy and messes up mass estimates.
First, dark energy was already commented on. But its' not clear how they
handled it at all because it was touched on for one sentence then
literally not discussed again.
Dark energy adds energy to systems, driving them apart. So in order to
accurately handle this you need to have an accurate model of how much
dark energy there is in the universe, which in turn comes from the exact
same sources that determine the cosmological amount of dark matter.
Plus, of course, it isn't clear at all how dark energy was accounted for
in this paper. The effect does _not_ get smaller as you increase the
scale. I see a discussion of clustering and how it tinkers with the mass
to luminosity ratio but the discussion seems to be relegated to the
references...
brad
Apr 26, 2012, 7:12:25 AM4/26/12
to
On Apr 25, 5:56 am, jacob navia <ja...@spamsink.net> wrote:
>
> In any case, these suggestions require modifications to the behavior of
> dark matter because their processes are not predicted in current models.
> None of these possibilities seem very attractive, leaving us with the
> conclusion that, assuming we live in a LCDM universe, a large fraction
> of the dark matter is gone missing.
A simple geometrical model can be formulated by postulating that the
>
> In any case, these suggestions require modifications to the behavior of
> dark matter because their processes are not predicted in current models.
> None of these possibilities seem very attractive, leaving us with the
> conclusion that, assuming we live in a LCDM universe, a large fraction
> of the dark matter is gone missing.
interface between the expanding space of the Voids and the bound space
of the filaments is actually the the intersection of two different
spacetime regimes with each possessing its own characteristic
geometry. An interface where two differing spacetime densities give
rise to a pseudo-gravitational field; via an increased spacetime
density. (as the expansion cannot enter the bound systems).
Brad
[Mod. note: 'citation needed' -- mjh]
jacob navia
Apr 26, 2012, 8:12:14 AM4/26/12
to
Le 26/04/12 13:11, eric gisse a écrit :
postulating dark matter remain. I never discussed that. What I wanted to
emphasize is that dark matter itself isn't detected, i.e. there are
strong reasons to believe it doesn't exist. There must be a different
explanation for the "missing mass" then and the problem is posed again
since "dark matter" can't be an explanation.
> You seem to have missed the resultant technical discussion as well.
>
Mr Helbig presented a viewpoint that is contrary to mine. My objective
was precisely to start a discussion, not to present a "new theory" of
something. I did not miss any discussion, and have followed all replies.
> As far as that article is concerned...I have an extremely large volume
> of skepticism regarding the result.
>
> Lets take the result at face value first, that the local matter density
> is a factor of 3 or so smaller than the global value. Why is that a
> problem?
>
> The universe is already known to be inhomogeneus and we have repeatedly
> seen that there are spots (the great void for example) in the universe
> quite a bit bigger than the locally surveyed volume which have even less
> "stuff".
>
> Repeating this observation within the void would get what result do you
> imagine?
>
In other terms you postulate that the astronomer making that survey hit
a "void" of dark matter by chance.
Great. That is a possible explanation but is it a plausible one?
> jacob navia<ja...@spamsink.net> wrote in
> news:mt2.0-400-...@hydra.herts.ac.uk:
>
>> Contrary to what I believed, the article of ESO that I pointed out
>> last week is by far not the only serious article that cast doubts in
>> the very existence of dark matter.
>
> The article you posted last week has literally no bearing on the reasons
> we believe dark matter exists.
>
Yes, because (as I have repeated several times) the reasons for
> news:mt2.0-400-...@hydra.herts.ac.uk:
>
>> Contrary to what I believed, the article of ESO that I pointed out
>> last week is by far not the only serious article that cast doubts in
>> the very existence of dark matter.
>
> The article you posted last week has literally no bearing on the reasons
> we believe dark matter exists.
>
postulating dark matter remain. I never discussed that. What I wanted to
emphasize is that dark matter itself isn't detected, i.e. there are
strong reasons to believe it doesn't exist. There must be a different
explanation for the "missing mass" then and the problem is posed again
since "dark matter" can't be an explanation.
> You seem to have missed the resultant technical discussion as well.
>
was precisely to start a discussion, not to present a "new theory" of
something. I did not miss any discussion, and have followed all replies.
> As far as that article is concerned...I have an extremely large volume
> of skepticism regarding the result.
>
> Lets take the result at face value first, that the local matter density
> is a factor of 3 or so smaller than the global value. Why is that a
> problem?
>
> The universe is already known to be inhomogeneus and we have repeatedly
> seen that there are spots (the great void for example) in the universe
> quite a bit bigger than the locally surveyed volume which have even less
> "stuff".
>
> Repeating this observation within the void would get what result do you
> imagine?
>
a "void" of dark matter by chance.
Great. That is a possible explanation but is it a plausible one?
eric gisse
Apr 26, 2012, 4:34:27 PM4/26/12
to
jacob navia <ja...@spamsink.net> wrote in news:mt2.0-13168-1335442334
@hydra.herts.ac.uk:
> Le 26/04/12 13:11, eric gisse a écrit :
>> jacob navia<ja...@spamsink.net> wrote in
>> news:mt2.0-400-...@hydra.herts.ac.uk:
>>
>>> Contrary to what I believed, the article of ESO that I pointed out
>>> last week is by far not the only serious article that cast doubts in
>>> the very existence of dark matter.
>>
>> The article you posted last week has literally no bearing on the
reasons
>> we believe dark matter exists.
>>
>
> Yes, because (as I have repeated several times) the reasons for
> postulating dark matter remain. I never discussed that. What I wanted
to
> emphasize is that dark matter itself isn't detected, i.e. there are
> strong reasons to believe it doesn't exist. There must be a different
> explanation for the "missing mass" then and the problem is posed again
> since "dark matter" can't be an explanation.
And why can't dark matter be an explanation? These two current issues
don't put a real dent in the theory.
Plus I had two technical arguments against the paper but they were
ignored.
You really need to read the papers you cite a bit more carefully.
[...]
> In other terms you postulate that the astronomer making that survey hit
> a "void" of dark matter by chance.
No, that is not what I'm saying.
What I am saying, again, is that there are locations that we know of in
the universe that if one were to repeat this exact same observation in
the void, you are going to get a very tiny amount of matter.
@hydra.herts.ac.uk:
> Le 26/04/12 13:11, eric gisse a écrit :
>> jacob navia<ja...@spamsink.net> wrote in
>> news:mt2.0-400-...@hydra.herts.ac.uk:
>>
>>> Contrary to what I believed, the article of ESO that I pointed out
>>> last week is by far not the only serious article that cast doubts in
>>> the very existence of dark matter.
>>
>> The article you posted last week has literally no bearing on the
reasons
>> we believe dark matter exists.
>>
>
> Yes, because (as I have repeated several times) the reasons for
> postulating dark matter remain. I never discussed that. What I wanted
to
> emphasize is that dark matter itself isn't detected, i.e. there are
> strong reasons to believe it doesn't exist. There must be a different
> explanation for the "missing mass" then and the problem is posed again
> since "dark matter" can't be an explanation.
don't put a real dent in the theory.
Plus I had two technical arguments against the paper but they were
ignored.
You really need to read the papers you cite a bit more carefully.
[...]
> In other terms you postulate that the astronomer making that survey hit
> a "void" of dark matter by chance.
What I am saying, again, is that there are locations that we know of in
the universe that if one were to repeat this exact same observation in
the void, you are going to get a very tiny amount of matter.
jacob navia
Apr 27, 2012, 2:51:57 AM4/27/12
to
Le 24/04/12 20:10, jacob navia a écrit :
http://www.sciencedaily.com/releases/2012/04/120425094352.htm
The scientific paper is here:
http://arxiv.org/abs/1204.5176
I cite the abstract:
<quote>
It has been known for a long time that the satellite galaxies of the
Milky Way (MW) show a significant amount of phase-space correlation,
they are distributed in a highly inclined Disc of Satellites (DoS). We
have extended the previous studies on the DoS by analysing for the first
time the orientations of streams of stars and gas, and the distributions
of globular clusters within the halo of the MW.
It is shown that the spatial distribution of MW globular clusters
classified as young halo clusters (YH GC) is very similar to the DoS,
while 7 of the 14 analysed streams align with the DoS. The probability
to find the observed clustering of streams is only 0.3 per cent when
assuming isotropy. The MW thus is surrounded by a vast polar structure
(VPOS) of subsystems (satellite galaxies, globular clusters and
streams), spreading from Galactocentric distances as small as 10 kpc out
to 250 kpc. These findings demonstrate that a near-isotropic infall of
cosmological sub-structure components onto the MW is essentially ruled
out because a large number of infalling objects would have had to be
highly correlated, to a degree not natural for dark matter
sub-structures. The majority of satellites, streams and YH GCs had to be
formed as a correlated population. This is possible in tidal tails
consisting of material expelled from interacting galaxies. We discuss
the tidal scenario for the formation of the VPOS, including successes
and possible challenges. The potential consequences of the MW satellites
being tidal dwarf galaxies are severe. If all the satellite galaxies and
YH GCs have been formed in an encounter between the young MW and another
gas-rich galaxy about 10-11 Gyr ago, then the MW does not have any
luminous dark-matter substructures and the missing satellites problem
becomes a catastrophic failure of the standard cosmological model.
<end quote>
<A catastrophic failure of the standard cosmological model>
Well, these authors do not hide any more behind "technical terms"...
They discovered that a HUGE disk perpendicular to the Milky Way exists
that can't be explained with the dark matter accretion models since it
proves that those satellite galaxies are NOT just in random positions
but in a plane.
> Contrary to what I believed, the article of ESO that I pointed out last
> week is by far not the only serious article that cast doubts in the very
> existence of dark matter.
>
Another one appeared yesterday in "Science daily":
> week is by far not the only serious article that cast doubts in the very
> existence of dark matter.
>
http://www.sciencedaily.com/releases/2012/04/120425094352.htm
The scientific paper is here:
http://arxiv.org/abs/1204.5176
I cite the abstract:
<quote>
It has been known for a long time that the satellite galaxies of the
Milky Way (MW) show a significant amount of phase-space correlation,
they are distributed in a highly inclined Disc of Satellites (DoS). We
have extended the previous studies on the DoS by analysing for the first
time the orientations of streams of stars and gas, and the distributions
of globular clusters within the halo of the MW.
It is shown that the spatial distribution of MW globular clusters
classified as young halo clusters (YH GC) is very similar to the DoS,
while 7 of the 14 analysed streams align with the DoS. The probability
to find the observed clustering of streams is only 0.3 per cent when
assuming isotropy. The MW thus is surrounded by a vast polar structure
(VPOS) of subsystems (satellite galaxies, globular clusters and
streams), spreading from Galactocentric distances as small as 10 kpc out
to 250 kpc. These findings demonstrate that a near-isotropic infall of
cosmological sub-structure components onto the MW is essentially ruled
out because a large number of infalling objects would have had to be
highly correlated, to a degree not natural for dark matter
sub-structures. The majority of satellites, streams and YH GCs had to be
formed as a correlated population. This is possible in tidal tails
consisting of material expelled from interacting galaxies. We discuss
the tidal scenario for the formation of the VPOS, including successes
and possible challenges. The potential consequences of the MW satellites
being tidal dwarf galaxies are severe. If all the satellite galaxies and
YH GCs have been formed in an encounter between the young MW and another
gas-rich galaxy about 10-11 Gyr ago, then the MW does not have any
luminous dark-matter substructures and the missing satellites problem
becomes a catastrophic failure of the standard cosmological model.
<end quote>
<A catastrophic failure of the standard cosmological model>
Well, these authors do not hide any more behind "technical terms"...
They discovered that a HUGE disk perpendicular to the Milky Way exists
that can't be explained with the dark matter accretion models since it
proves that those satellite galaxies are NOT just in random positions
but in a plane.
Phillip Helbig---undress to reply
Apr 27, 2012, 2:53:36 AM4/27/12
to
In article <mt2.0-13168...@hydra.herts.ac.uk>, jacob navia
idea of a neutrino (also a sort of missing mass in nuclear reactions)
and its detection---and in the case of neutrinos, we have very strong
sources. If dark matter is some sort of weakly interacting massive
particle, then it is no surprise that it is difficult to detect.
Absence of evidence is not evidence of absence. :-)
> In other terms you postulate that the astronomer making that survey hit
> a "void" of dark matter by chance.
>
> Great. That is a possible explanation but is it a plausible one?
Not necessarily a void. The neighbourhood of the Sun was explored.
Current ideas indicate less dark matter at the centre of galaxies and
much at the edges (the classic flat rotation curves are obseved much
farther out than the Sun). Since dark matter doesn't interact
electromagnetically (which is why it is dark), it can't clump by
radiating away energy like baryons can, so this distribution is not ad
hoc. However, we don't know what it exactly is.
<ja...@spamsink.net> writes:
> > The article you posted last week has literally no bearing on the reasons
> > we believe dark matter exists.
>
> Yes, because (as I have repeated several times) the reasons for
> postulating dark matter remain. I never discussed that. What I wanted to
> emphasize is that dark matter itself isn't detected, i.e. there are
> strong reasons to believe it doesn't exist. There must be a different
> explanation for the "missing mass" then and the problem is posed again
> since "dark matter" can't be an explanation.
This is a non-sequitur. It was several decades between the theoretical
> > The article you posted last week has literally no bearing on the reasons
> > we believe dark matter exists.
>
> Yes, because (as I have repeated several times) the reasons for
> postulating dark matter remain. I never discussed that. What I wanted to
> emphasize is that dark matter itself isn't detected, i.e. there are
> strong reasons to believe it doesn't exist. There must be a different
> explanation for the "missing mass" then and the problem is posed again
> since "dark matter" can't be an explanation.
idea of a neutrino (also a sort of missing mass in nuclear reactions)
and its detection---and in the case of neutrinos, we have very strong
sources. If dark matter is some sort of weakly interacting massive
particle, then it is no surprise that it is difficult to detect.
Absence of evidence is not evidence of absence. :-)
> In other terms you postulate that the astronomer making that survey hit
> a "void" of dark matter by chance.
>
> Great. That is a possible explanation but is it a plausible one?
Current ideas indicate less dark matter at the centre of galaxies and
much at the edges (the classic flat rotation curves are obseved much
farther out than the Sun). Since dark matter doesn't interact
electromagnetically (which is why it is dark), it can't clump by
radiating away energy like baryons can, so this distribution is not ad
hoc. However, we don't know what it exactly is.
Phillip Helbig---undress to reply
Apr 27, 2012, 3:46:12 AM4/27/12
to
In article <mt2.0-4367...@hydra.herts.ac.uk>, eric gisse
effects of dark energy are negligible. That's why there was no firm
evidence for it until high-redshift supernovae, the CMB etc were
observed in detail.
<jowr.pi...@gmail.com> writes:
> 2) Dark energy and messes up mass estimates.
>
> First, dark energy was already commented on. But its' not clear how they
> handled it at all because it was touched on for one sentence then
> literally not discussed again.
>
> Dark energy adds energy to systems, driving them apart. So in order to
> accurately handle this you need to have an accurate model of how much
> dark energy there is in the universe, which in turn comes from the exact
> same sources that determine the cosmological amount of dark matter.
>
> Plus, of course, it isn't clear at all how dark energy was accounted for
> in this paper. The effect does _not_ get smaller as you increase the
> scale. I see a discussion of clustering and how it tinkers with the mass
> to luminosity ratio but the discussion seems to be relegated to the
> references...
I agree with the stuff I didn't quote. :-) At the scales involved, the
> 2) Dark energy and messes up mass estimates.
>
> First, dark energy was already commented on. But its' not clear how they
> handled it at all because it was touched on for one sentence then
> literally not discussed again.
>
> Dark energy adds energy to systems, driving them apart. So in order to
> accurately handle this you need to have an accurate model of how much
> dark energy there is in the universe, which in turn comes from the exact
> same sources that determine the cosmological amount of dark matter.
>
> Plus, of course, it isn't clear at all how dark energy was accounted for
> in this paper. The effect does _not_ get smaller as you increase the
> scale. I see a discussion of clustering and how it tinkers with the mass
> to luminosity ratio but the discussion seems to be relegated to the
> references...
effects of dark energy are negligible. That's why there was no firm
evidence for it until high-redshift supernovae, the CMB etc were
observed in detail.
Nicolaas Vroom
Apr 29, 2012, 12:21:40 PM4/29/12
to
Op donderdag 26 april 2012 10:33:45 UTC+2 schreef Phillip Helbig---undress to reply het volgende:
See http://en.wikipedia.org/wiki/Friedmann_equations
"To test this" What do you mean ?
To test the # 0.28, or the numbers 83 and 17 ?
"To sum up ALL the mass" is not simple.
With mass do you mean all matter formed out of atoms
including all gas clouds ?
If this is the case than it is difficult, even impossible.
> Right, but how do you "sum up all the mass"? If you can't see it, you
> have to estimate it by its dynamical effects. However, these are
> produced by gradients in mass distributions. Any dark matter smoothly
> distributed on the scale surveyed is not detectable by dynamical
> methods.
>
> Actually, the idea of dark matter arose because when one "sums up all
> the mass" of visible matter, one needs more matter to explain dynamic
> effects (e.g. flat rotation curves of galaxies). So, this is not a new
> idea. WE DON'T KNOW WHAT THE DARK MATTER IS.
I think it is important here to make a distinction between:
1. visible matter (atoms), 2. invisible matter (atoms, gas clouds) and
3. dark matter (not atomair)
If you cannot explain a flat curve using type 1 than you can use in principle
any combination of type 2 and 3 to fill the gap.
However you must take care that first all matter of type 2 is included, before
type 3 can be included with confidence.
Telescopes are becoming better. This means the amount of type 1 observed
increases. This inturn indicates that there was more type 2 available and
indirectly limits the necessity of type 3 matter.
If you want to estimate the mass of a galaxy does the scientific community
agree that the disc size of a galaxy is larger than the size of the
observed galaxy rotation curve ?
If that is correct than this means that the disc size is larger and more
masif, making the necessity of a halo of matter smaller.
Nicolaas Vroom
http://users.pandora.be/nicvroom/
> In article <mt2.0-29923...@hydra.herts.ac.uk>, jacob navia
> <ja...@spamsink.net> writes:
>
> > The idea is as simple as it is brilliant: cosmology has precise
> > predictions as to what is the content of our universe. In particular, it
> > predicts the density of matter to be Ωm,glob = 0.28 +- 0.03 (83 per cent
> > of this in dark, 17 per cent in luminous matter). Now, to test this, all
> > you have to do is to sum up all the mass within a certain volume of
> > space, and you can estimate the actual density of mass within that
> > volume.
Omega m = rho m / rho c
> <ja...@spamsink.net> writes:
>
> > The idea is as simple as it is brilliant: cosmology has precise
> > predictions as to what is the content of our universe. In particular, it
> > predicts the density of matter to be Ωm,glob = 0.28 +- 0.03 (83 per cent
> > of this in dark, 17 per cent in luminous matter). Now, to test this, all
> > you have to do is to sum up all the mass within a certain volume of
> > space, and you can estimate the actual density of mass within that
> > volume.
See http://en.wikipedia.org/wiki/Friedmann_equations
"To test this" What do you mean ?
To test the # 0.28, or the numbers 83 and 17 ?
"To sum up ALL the mass" is not simple.
With mass do you mean all matter formed out of atoms
including all gas clouds ?
If this is the case than it is difficult, even impossible.
> Right, but how do you "sum up all the mass"? If you can't see it, you
> have to estimate it by its dynamical effects. However, these are
> produced by gradients in mass distributions. Any dark matter smoothly
> distributed on the scale surveyed is not detectable by dynamical
> methods.
>
> Actually, the idea of dark matter arose because when one "sums up all
> the mass" of visible matter, one needs more matter to explain dynamic
> effects (e.g. flat rotation curves of galaxies). So, this is not a new
> idea. WE DON'T KNOW WHAT THE DARK MATTER IS.
1. visible matter (atoms), 2. invisible matter (atoms, gas clouds) and
3. dark matter (not atomair)
If you cannot explain a flat curve using type 1 than you can use in principle
any combination of type 2 and 3 to fill the gap.
However you must take care that first all matter of type 2 is included, before
type 3 can be included with confidence.
Telescopes are becoming better. This means the amount of type 1 observed
increases. This inturn indicates that there was more type 2 available and
indirectly limits the necessity of type 3 matter.
If you want to estimate the mass of a galaxy does the scientific community
agree that the disc size of a galaxy is larger than the size of the
observed galaxy rotation curve ?
If that is correct than this means that the disc size is larger and more
masif, making the necessity of a halo of matter smaller.
Nicolaas Vroom
http://users.pandora.be/nicvroom/
Phillip Helbig---undress to reply
Apr 29, 2012, 3:35:28 PM4/29/12
to
In article <mt2.0-32514...@hydra.herts.ac.uk>, Nicolaas Vroom
1 is visible baryonic matter, 2 is invisible baryonic matter and 3 is
invisible non-baryonic matter.
> If you cannot explain a flat curve using type 1 than you can use in principle
> any combination of type 2 and 3 to fill the gap.
No, because we have a limit on the sum of 1 and 2 (i.e. on the baryonic
matter) from primordial nucleosynthesis.
> However you must take care that first all matter of type 2 is included,
> before type 3 can be included with confidence.
Even if the maximum amount of baryonic matter is included, then one
still needs type 3.
<nicolaa...@pandora.be> writes:
> I think it is important here to make a distinction between:
> 1. visible matter (atoms), 2. invisible matter (atoms, gas clouds) and
> 3. dark matter (not atomair)
1 and 2 are usually termed "baryonic matter" and 2 and 3 "dark matter".
> I think it is important here to make a distinction between:
> 1. visible matter (atoms), 2. invisible matter (atoms, gas clouds) and
> 3. dark matter (not atomair)
1 is visible baryonic matter, 2 is invisible baryonic matter and 3 is
invisible non-baryonic matter.
> If you cannot explain a flat curve using type 1 than you can use in principle
> any combination of type 2 and 3 to fill the gap.
matter) from primordial nucleosynthesis.
> However you must take care that first all matter of type 2 is included,
> before type 3 can be included with confidence.
still needs type 3.
Nicolaas Vroom
May 1, 2012, 12:12:53 PM5/1/12
to
Op zondag 29 april 2012 21:35:28 UTC+2 schreef Phillip Helbig---undress to reply het volgende:
> > If you cannot explain a flat curve using type 1 than you can use in principle
> > any combination of type 2 and 3 to fill the gap.
>
> No, because we have a limit on the sum of 1 and 2 (i.e. on the baryonic
> matter) from primordial nucleosynthesis.
What do you mean by limit ? A maximum limit of for example 80% ?
Or do you mean the amount of each in our Galaxy is already decided/fixed
during the Big Bang period ? (and stayed fixed thereafter ?)
> > However you must take care that first all matter of type 2 is included,
> > before type 3 can be included with confidence.
>
> Even if the maximum amount of baryonic matter is included, then one
> still needs type 3.
Almost the same question: why ?
If I understand you correct;
Suppose someone claims: "We have observed so much visible matter in the
Andromeda Galaxy that we do not need any dark matter type 3"
than your answer is: That is wrong.
Nicolaas Vroom
http://users.pandora.be/nicvroom/
> In article <mt2.0-32514...@hydra.herts.ac.uk>, Nicolaas Vroom
> <nicolaa...@pandora.be> writes:
>
> > I think it is important here to make a distinction between:
> > 1. visible matter (atoms), 2. invisible matter (atoms, gas clouds) and
> > 3. dark matter (not atomair)
>
> 1 and 2 are usually termed "baryonic matter" and 2 and 3 "dark matter".
> 1 is visible baryonic matter, 2 is invisible baryonic matter and 3 is
> invisible non-baryonic matter.
Agreed
> <nicolaa...@pandora.be> writes:
>
> > I think it is important here to make a distinction between:
> > 1. visible matter (atoms), 2. invisible matter (atoms, gas clouds) and
> > 3. dark matter (not atomair)
>
> 1 and 2 are usually termed "baryonic matter" and 2 and 3 "dark matter".
> 1 is visible baryonic matter, 2 is invisible baryonic matter and 3 is
> invisible non-baryonic matter.
> > If you cannot explain a flat curve using type 1 than you can use in principle
> > any combination of type 2 and 3 to fill the gap.
>
> No, because we have a limit on the sum of 1 and 2 (i.e. on the baryonic
> matter) from primordial nucleosynthesis.
Or do you mean the amount of each in our Galaxy is already decided/fixed
during the Big Bang period ? (and stayed fixed thereafter ?)
> > However you must take care that first all matter of type 2 is included,
> > before type 3 can be included with confidence.
>
> Even if the maximum amount of baryonic matter is included, then one
> still needs type 3.
If I understand you correct;
Suppose someone claims: "We have observed so much visible matter in the
Andromeda Galaxy that we do not need any dark matter type 3"
than your answer is: That is wrong.
Nicolaas Vroom
http://users.pandora.be/nicvroom/
Phillip Helbig---undress to reply
May 1, 2012, 2:58:52 PM5/1/12
to
In article <mt2.0-27225...@hydra.herts.ac.uk>, Nicolaas Vroom
is the Hubble constant, is fixed by big-bang nucleosynthesis. This
follows essentially from laboratory results from nuclear physics and the
temperature of the CMB. This is a robust result. We now know the
Hubble constant quite well, so we have a firm value for Omega_baryon
which is much less than the 0.28 for Omega_matter from cosmological
considerations and is even less than the matter associated with galaxies
based on dynamic measurements. Thus, most of the dark matter has to be
non-baryonic.
> Suppose someone claims: "We have observed so much visible matter in the
> Andromeda Galaxy that we do not need any dark matter type 3"
> than your answer is: That is wrong.
This has not been observed. If it were observed, it would imply that
more baryonic matter is observed than allowed by the nucleosynthesis
constraints. Of course, if someone actually observes this, then we will
have to think about it, but the dark-matter problem is that people
observe too LITTLE visible matter, not too much.
<nicolaa...@pandora.be> writes:
> > No, because we have a limit on the sum of 1 and 2 (i.e. on the baryonic
> > matter) from primordial nucleosynthesis.
>
> What do you mean by limit ? A maximum limit of for example 80% ?
> Or do you mean the amount of each in our Galaxy is already decided/fixed
> during the Big Bang period ? (and stayed fixed thereafter ?)
The baryon density, which is proportional to Omega_baryon*H^2, where H
> > No, because we have a limit on the sum of 1 and 2 (i.e. on the baryonic
> > matter) from primordial nucleosynthesis.
>
> What do you mean by limit ? A maximum limit of for example 80% ?
> Or do you mean the amount of each in our Galaxy is already decided/fixed
> during the Big Bang period ? (and stayed fixed thereafter ?)
is the Hubble constant, is fixed by big-bang nucleosynthesis. This
follows essentially from laboratory results from nuclear physics and the
temperature of the CMB. This is a robust result. We now know the
Hubble constant quite well, so we have a firm value for Omega_baryon
which is much less than the 0.28 for Omega_matter from cosmological
considerations and is even less than the matter associated with galaxies
based on dynamic measurements. Thus, most of the dark matter has to be
non-baryonic.
> Suppose someone claims: "We have observed so much visible matter in the
> Andromeda Galaxy that we do not need any dark matter type 3"
> than your answer is: That is wrong.
more baryonic matter is observed than allowed by the nucleosynthesis
constraints. Of course, if someone actually observes this, then we will
have to think about it, but the dark-matter problem is that people
observe too LITTLE visible matter, not too much.
Nicolaas Vroom
May 2, 2012, 8:41:14 AM5/2/12
to
Op dinsdag 1 mei 2012 20:58:52 UTC+2 schreef Phillip Helbig het volgende:
From the book Galactic Dynamics 1994 Chapter 10 "Dark matter and cosmology"
I get that Omega B is between 0.011 and 0.19. That means Omega dm is larger
than 0.09 ?
Assuming Omega 0 = 1 That means Omega (L or DE) = 1-0.28 = 0.72
It is important to make a clear difference what we are discussing:
The Universe or a single Galaxy.
At page 630 we read:
"Thus stellar remmants COULD supply all the dark mass in the solar neighborhood
but not all the dark mass in clusters of galaxies or the Virgo supercluster"
This implies that the amount of non-baryonic dark matter could be zero in our
galaxy.
The sentence before read:
"The density in such remnants should not exceed Omega 0 as 0.03 or else their
integrated light output etc"
IMO remnants should include planet sized objects.
> > Suppose someone claims: "We have observed so much visible matter in the
> > Andromeda Galaxy that we do not need any dark matter type 3"
> > than your answer is: That is wrong.
>
> This has not been observed. If it were observed, it would imply that
> more baryonic matter is observed than allowed by the nucleosynthesis
> constraints. Of course, if someone actually observes this, then we will
> have to think about it, but the dark-matter problem is that people
> observe too LITTLE visible matter, not too much.
The issue is the amount of baryonic dark matter in our Galaxy which
cannot be observed. In any simulation this must be included.
Part of the issue is the size (shape) of the disc. IMO you should take
into account that the size is larger than observed.
Nicolaas Vroom
http://users.pandora.be/nicvroom/
> In article <mt2.0-27225...@hydra.herts.ac.uk>, Nicolaas Vroom
> <nicolaa...@pandora.be> writes:
>
> > > No, because we have a limit on the sum of 1 and 2 (i.e. on the baryonic
> > > matter) from primordial nucleosynthesis.
> >
> > What do you mean by limit ? A maximum limit of for example 80% ?
> > Or do you mean the amount of each in our Galaxy is already decided/fixed
> > during the Big Bang period ? (and stayed fixed thereafter ?)
>
> The baryon density, which is proportional to Omega_baryon*H^2, where H
> is the Hubble constant, is fixed by big-bang nucleosynthesis.
> <nicolaa...@pandora.be> writes:
>
> > > No, because we have a limit on the sum of 1 and 2 (i.e. on the baryonic
> > > matter) from primordial nucleosynthesis.
> >
> > What do you mean by limit ? A maximum limit of for example 80% ?
> > Or do you mean the amount of each in our Galaxy is already decided/fixed
> > during the Big Bang period ? (and stayed fixed thereafter ?)
>
> The baryon density, which is proportional to Omega_baryon*H^2, where H
> is the Hubble constant, is fixed by big-bang nucleosynthesis.
> We now know the
> Hubble constant quite well, so we have a firm value for Omega_baryon
> which is much less than the 0.28 for Omega_matter from cosmological
> considerations and is even less than the matter associated with galaxies
> based on dynamic measurements. Thus, most of the dark matter has to be
> non-baryonic.
Do I understand you correct?
> Hubble constant quite well, so we have a firm value for Omega_baryon
> which is much less than the 0.28 for Omega_matter from cosmological
> considerations and is even less than the matter associated with galaxies
> based on dynamic measurements. Thus, most of the dark matter has to be
> non-baryonic.
From the book Galactic Dynamics 1994 Chapter 10 "Dark matter and cosmology"
I get that Omega B is between 0.011 and 0.19. That means Omega dm is larger
than 0.09 ?
Assuming Omega 0 = 1 That means Omega (L or DE) = 1-0.28 = 0.72
It is important to make a clear difference what we are discussing:
The Universe or a single Galaxy.
At page 630 we read:
"Thus stellar remmants COULD supply all the dark mass in the solar neighborhood
but not all the dark mass in clusters of galaxies or the Virgo supercluster"
This implies that the amount of non-baryonic dark matter could be zero in our
galaxy.
The sentence before read:
"The density in such remnants should not exceed Omega 0 as 0.03 or else their
integrated light output etc"
IMO remnants should include planet sized objects.
> > Suppose someone claims: "We have observed so much visible matter in the
> > Andromeda Galaxy that we do not need any dark matter type 3"
> > than your answer is: That is wrong.
>
> This has not been observed. If it were observed, it would imply that
> more baryonic matter is observed than allowed by the nucleosynthesis
> constraints. Of course, if someone actually observes this, then we will
> have to think about it, but the dark-matter problem is that people
> observe too LITTLE visible matter, not too much.
cannot be observed. In any simulation this must be included.
Part of the issue is the size (shape) of the disc. IMO you should take
into account that the size is larger than observed.
Nicolaas Vroom
http://users.pandora.be/nicvroom/
Phillip Helbig---undress to reply
May 3, 2012, 1:52:38 AM5/3/12
to
In article <mt2.0-27934...@hydra.herts.ac.uk>, Nicolaas Vroom
later.
> That means Omega dm is larger
> than 0.09 ?
Right, assuming 0.19 as an upper limit to Omega_B, which is probably an
overestimate.
> Assuming Omega 0 = 1 That means Omega (L or DE) = 1-0.28 = 0.72
Right.
> It is important to make a clear difference what we are discussing:
> The Universe or a single Galaxy.
In the former case, almost always the total Omega (excluding lambda) is
what is meant by 0.28.
> At page 630 we read:
> "Thus stellar remmants COULD supply all the dark mass in the solar neighborhood
> but not all the dark mass in clusters of galaxies or the Virgo supercluster"
Right.
> This implies that the amount of non-baryonic dark matter could be zero in our
> galaxy.
A lot has happened since 1994 (and presumably the book was actually
written even before that).
> The sentence before read:
> "The density in such remnants should not exceed Omega 0 as 0.03 or else their
> integrated light output etc"
> IMO remnants should include planet sized objects.
Yes, but you have to have a plausible scenario to make lots of planets
but not too many stars.
> The issue is the amount of baryonic dark matter in our Galaxy which
> cannot be observed. In any simulation this must be included.
> Part of the issue is the size (shape) of the disc. IMO you should take
> into account that the size is larger than observed.
I'm not sure what you mean here. How do you know it is larger than
observed?
<nicolaa...@pandora.be> writes:
> Do I understand you correct?
> From the book Galactic Dynamics 1994 Chapter 10 "Dark matter and cosmology"
> I get that Omega B is between 0.011 and 0.19.
I think the constraints are tighter than that now, almost 20 years
> Do I understand you correct?
> From the book Galactic Dynamics 1994 Chapter 10 "Dark matter and cosmology"
> I get that Omega B is between 0.011 and 0.19.
later.
> That means Omega dm is larger
> than 0.09 ?
overestimate.
> Assuming Omega 0 = 1 That means Omega (L or DE) = 1-0.28 = 0.72
> It is important to make a clear difference what we are discussing:
> The Universe or a single Galaxy.
what is meant by 0.28.
> At page 630 we read:
> "Thus stellar remmants COULD supply all the dark mass in the solar neighborhood
> but not all the dark mass in clusters of galaxies or the Virgo supercluster"
> This implies that the amount of non-baryonic dark matter could be zero in our
> galaxy.
written even before that).
> The sentence before read:
> "The density in such remnants should not exceed Omega 0 as 0.03 or else their
> integrated light output etc"
> IMO remnants should include planet sized objects.
but not too many stars.
> The issue is the amount of baryonic dark matter in our Galaxy which
> cannot be observed. In any simulation this must be included.
> Part of the issue is the size (shape) of the disc. IMO you should take
> into account that the size is larger than observed.
observed?
Nicolaas Vroom
May 4, 2012, 10:29:47 AM5/4/12
to
Op donderdag 3 mei 2012 07:52:38 UTC+2 schreef Phillip Helbig het volgende:
http://connection.ebscohost.com/c/articles/9301032385/grand-illusion
It claims: "Hot B,A and F stars along with cool giants G make up most of
the brightest stars (At top side of picture) but cool K dwarfs and red
dwarfs and hot but small white dwarfs account for 95% of all stars
(At bottom of the picture)"
B
AF
GGG
KKKKKKK
RRRRRWRRRRRRRRWRRR
RRRRRRRRRRRWRRRRRRRWRRRRRRRWRRRRRWRRRRWRRRRR
The question is how much baryonic mass 95% stars is.
However much more invisible mass should be considered:
the planet sized objects, asteroids and gas clouds.
> > The issue is the amount of baryonic dark matter in our Galaxy which
> > cannot be observed. In any simulation this must be included.
> > Part of the issue is the size (shape) of the disc. IMO you should take
> > into account that the size is larger than observed.
>
> I'm not sure what you mean here. How do you know it is larger than
> observed?
Consider: http://en.wikipedia.org/wiki/Milky_Way#Composition_and_structure
The visible radius of the Milky way is roughly (75000+30000)/2 = 50000 ly
However the real radius of the rotating galaxy is much larger. Maybe
100000 ly which contains baryonic invisible matter.
The text reads:
"Most of the matter of the Galaxy is thought to be darkmatter, which forms
a dark matter halo" etc.
I have no problem with the first if they mean baryonic matter.
You only have to consider a halo if the amount of baryonic matter
in bulge and disc (Visisble and invisible) is not enough
to simulate the galaxy rotation curve.
The article at page 48 IMO takes a much more common sense approach.
"These halos must consist of faint or invisible objects called dm etc
It could be faint stars, like red dwarfs and white dwarfs or it
could be subatomic particles etc"
Nicolaas Vroom
http://users.pandora.be/nicvroom/
> In article <mt2.0-27934...@hydra.herts.ac.uk>, Nicolaas Vroom
> <nicolaa...@pandora.be> writes:
>
> > The sentence before read:
> > "The density in such remnants should not exceed Omega 0 as 0.03 or else their
> > integrated light output etc"
> > IMO remnants should include planet sized objects.
>
> Yes, but you have to have a plausible scenario to make lots of planets
> but not too many stars.
One reason is this document from 1992:
> <nicolaa...@pandora.be> writes:
>
> > The sentence before read:
> > "The density in such remnants should not exceed Omega 0 as 0.03 or else their
> > integrated light output etc"
> > IMO remnants should include planet sized objects.
>
> Yes, but you have to have a plausible scenario to make lots of planets
> but not too many stars.
http://connection.ebscohost.com/c/articles/9301032385/grand-illusion
It claims: "Hot B,A and F stars along with cool giants G make up most of
the brightest stars (At top side of picture) but cool K dwarfs and red
dwarfs and hot but small white dwarfs account for 95% of all stars
(At bottom of the picture)"
B
AF
GGG
KKKKKKK
RRRRRWRRRRRRRRWRRR
RRRRRRRRRRRWRRRRRRRWRRRRRRRWRRRRRWRRRRWRRRRR
The question is how much baryonic mass 95% stars is.
However much more invisible mass should be considered:
the planet sized objects, asteroids and gas clouds.
> > The issue is the amount of baryonic dark matter in our Galaxy which
> > cannot be observed. In any simulation this must be included.
> > Part of the issue is the size (shape) of the disc. IMO you should take
> > into account that the size is larger than observed.
>
> I'm not sure what you mean here. How do you know it is larger than
> observed?
The visible radius of the Milky way is roughly (75000+30000)/2 = 50000 ly
However the real radius of the rotating galaxy is much larger. Maybe
100000 ly which contains baryonic invisible matter.
The text reads:
"Most of the matter of the Galaxy is thought to be darkmatter, which forms
a dark matter halo" etc.
I have no problem with the first if they mean baryonic matter.
You only have to consider a halo if the amount of baryonic matter
in bulge and disc (Visisble and invisible) is not enough
to simulate the galaxy rotation curve.
The article at page 48 IMO takes a much more common sense approach.
"These halos must consist of faint or invisible objects called dm etc
It could be faint stars, like red dwarfs and white dwarfs or it
could be subatomic particles etc"
Nicolaas Vroom
http://users.pandora.be/nicvroom/
Phillip Helbig---undress to reply
May 5, 2012, 4:06:52 PM5/5/12
to
In article <mt2.0-6862...@hydra.herts.ac.uk>, Nicolaas Vroom
In general, try to find more recent references. A lot has happened in
the last 20 years. Not all old stuff is wrong, of course.
> It claims: "Hot B,A and F stars along with cool giants G make up most of
> the brightest stars (At top side of picture) but cool K dwarfs and red
> dwarfs and hot but small white dwarfs account for 95% of all stars
> (At bottom of the picture)"
OK.
> The question is how much baryonic mass 95% stars is.
> However much more invisible mass should be considered:
> the planet sized objects, asteroids and gas clouds.
Yes, but they are so much less massive than stars that you would have to
have orders of magnitude more of these than stars exist.
> Consider: http://en.wikipedia.org/wiki/Milky_Way#Composition_and_structure
> The visible radius of the Milky way is roughly (75000+30000)/2 = 50000 ly
> However the real radius of the rotating galaxy is much larger. Maybe
> 100000 ly which contains baryonic invisible matter.
> The text reads:
> "Most of the matter of the Galaxy is thought to be darkmatter, which forms
> a dark matter halo" etc.
Yes, but no-one observed it. It's a hypothesis. I'm not saying it's
wrong, but on the one hand you seem to say "stick to observations" but
on the other hand assume something which comes out of theory.
In general, try to find more recent references. A lot has happened in
the last 20 years. Not all old stuff is wrong, of course.
> It claims: "Hot B,A and F stars along with cool giants G make up most of
> the brightest stars (At top side of picture) but cool K dwarfs and red
> dwarfs and hot but small white dwarfs account for 95% of all stars
> (At bottom of the picture)"
> The question is how much baryonic mass 95% stars is.
> However much more invisible mass should be considered:
> the planet sized objects, asteroids and gas clouds.
have orders of magnitude more of these than stars exist.
> Consider: http://en.wikipedia.org/wiki/Milky_Way#Composition_and_structure
> The visible radius of the Milky way is roughly (75000+30000)/2 = 50000 ly
> However the real radius of the rotating galaxy is much larger. Maybe
> 100000 ly which contains baryonic invisible matter.
> The text reads:
> "Most of the matter of the Galaxy is thought to be darkmatter, which forms
> a dark matter halo" etc.
wrong, but on the one hand you seem to say "stick to observations" but
on the other hand assume something which comes out of theory.
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