CDM Cosmology (was formation of dwarf galaxies in CDM cosmology)

"Jonathan Thornburg" schreef in bericht
...
From: "Jonathan Thornburg [remove -animal to reply]"

Subject: formation of dwarf galaxies in CDM cosmology
Newsgroups: sci.astro.research

Robert L. Oldershaw wrote:
In the Jan. 14th issue of Nature is a paper that claims to resolve a
serious problem that has plagued the CDM cosmology for a long time.

For the benefit of others, the paper in question is this one:

F. Governato, C. Brook, L. Mayer, A. Brooks, G. Rhee, J. Wadsley,
P. Jonsson, B. Willman, G. Stinson, T. Quinn & P. Madau
"Bulgeless dwarf galaxies and dark matter cores
from supernova-driven outflows"
Abstract:
For almost two decades the properties of `dwarf' galaxies have
challenged the cold dark matter (CDM) model of galaxy formation1.
Most observed dwarf galaxies consist of a rotating stellar disk2
embedded in a massive dark-matter halo with a near-constant-density
core3. Models based on the dominance of CDM, however, invariably
form galaxies with dense spheroidal stellar bulges and steep central
dark-matter profiles4, 5, 6, because low-angular-momentum baryons
and dark matter sink to the centres of galaxies through accretion
and repeated mergers7. Processes that decrease the central density
of CDM halos8 have been identified, but have not yet reconciled
theory with observations of present-day dwarfs. This failure is
potentially catastrophic for the CDM model, possibly requiring a
different dark-matter particle candidate9. Here we report
hydrodynamical
simulations (in a framework10 assuming the presence of CDM and a
cosmological constant) in which the inhomogeneous interstellar
medium is resolved. Strong outflows from supernovae remove
low-angular-momentum gas, which inhibits the formation of bulges
and decreases the dark-matter density to less than half of what it
would otherwise be within the central kiloparsec. The analogues of
dwarf galaxies-bulgeless and with shallow central dark-matter
profiles-arise naturally in these simulations.
Nature volume 463, number 7278, pages 203-206 (14 Jan 2010)
http://www.nature.com/nature/journal...ture08640.html
doi:10.1038/nature08640
preprint (open-access!) at http://arxiv.org/abs/0911.2237

Nature also has an "Editor's summary" and a "News and Views" article
about this work,
Marla Geha
"Galaxy formation: Gone with the wind?"
Nature volume 463, number 7278, pages 167-168 (14 Jan 2010)
http://www.nature.com/nature/journal...l/463167a.html
doi:10.1038/463167a


What is CDM and why do we need this ?
Accordingly to the Book "The Big Bang" by Joseph Silk
At page 182 we read:
"The dark matter responds to gravity, and initial density fluctuations
grow in contrast, just as they do with ordinary matter"
That means the behaviour dark matter can be described by Newton's
Law, but it is different from ordinary matter i.e. dark matter is not
described by the chemical elements of the periodic table,
which are the building blocks of the Sun and the Earth.
If you combine those chemical elements in small quantities you get
small pieces (grains) of ordinary matter, which are all dark and cold.
Those pieces only become visible if they grow in size and become as
large as the size of the Earth and if the temperature increases
to more than 2000 degrees C at the outside! (There are exceptions)
What important is that those small pieces (objects) of cool ordinary
matter are impossible to detect.

This raises for me the question:
Why introducing CDM which consists of nonbaryonic particles.
See: http://en.wikipedia.org/wiki/Dark_matter
The answer is partly because the observed rotation curves
of galaxies don't match the calculated rotation curves based
on the observed(visible) values of ordinary matter.
One specific discrepancy is on the right side where the rotation
curve assumes high speeds of something while outside that region
(away from the bulge) no (visible) mass can be detected.
The solution is to invent the concept of (invisible) dark matter
(in a halo) which behaves mathematical the same as ordinary matter
but physical not. There exists no inter exchange.
I 'am astonished by this reasoning. Why not introducing ordinary
matter in small quantities (inside the disc) ? This is a much simpler
concept which allows for a free mixing (colliding) environment.

At page 167 at the above mentioned document we can read:
"Yet despite this uncertainty (hypothesized particle) the prevailing
model of galaxy formation based on CDM is tremendously
successful, predicting a vast range of observational data"
What I would like to know which data CDM predicts correct and
why a model only based on ordinary matter would fail based on
the same circumstances.
I think to describe the evolution in galaxy formation only using
ordinary matter is much simpler.
CDM models require supernova in order to move dark matter
outwards. Ordinary matter models are less strict.
The whole issue is how fast small objects form larger objects
which form stars at the same time converting invisible matter
into visible matter. This whole process depends about the initial
density of the original grain clouds.

Page 167 shows one image of a real galaxy (right) and one
simulation image of a galaxy. The right image shows ordinary
visible matter (stars). However this is only a part of the total
ordinary mass of that galaxy. What is not shown is a type of
small objects in the plane of the disc (like the Kuiper Belt)
and a type of Oord cloud within and surrounding the galaxy

Page 205 shows two galaxy rotation curves: The real one and
a simulation using CDM.
IMO simulating the same galaxy rotation using only ordinary
matter is not more difficult. In fact the total galaxy rotation curve
is much larger and stretches far into the Kuiper Belt.

Nicolaas Vroom
http://users.pandora.be/nicvroom

[Somewhat sorry for chopping unneeded attributions of the top
of this.]

Robert L. Oldershaw wrote:

In the Jan. 14th issue of Nature is a paper that
claims to resolve a serious problem that has
plagued the CDM cosmology for a long time.

I emphasize here the word "claims". As far as I
know, the situation is "resolves", full stop.

People who can't or won't do the math before
commenting shouldn't be casting aspersions on the
writings of those who can and do.

This is the tip of the iceberg of a larger problem.

This unaccepted resolution of a problem in an
existing theory brings to mind a failure (within my
knowledge) of the system of scientific journals in
general, which affects discussions here.

To show first how an alternative system works...

The Request for Comments series of Internet
Engineering Task Force papers,

http://rfc-editor.org/rfc-index.html

which are in many cases pretty much the law,
despite the mildness of the series title, for
how the Internet will work, are comprised of
papers submitted by interested participants and
reviewed and maintained available by the IETF
working body.

Each, in the above index, carries with it, among
other possible annotations, "updates", "is
updated by", "obsoletes", and "is obsoleted by".

This makes it possible to navigate easily to the
most current information.

Thus, one is not tempted to cite papers overcome
by events as if they were the current
understanding of matters.

This avoids the endless rounds of rediscussions of
already visited subjects based on superseded
information that is so prevalent in
sci.astro.research, one among several myriad of
similarly afflicted discussion forums, and many
instances of which have come on display here in the
weeks recently passed.

In part, this problem exists simply because there is
not a mechanism such as the one above for RFCs to
annotate a list of "all the journal articles since
the inventtion of writing", that update or obsolete
earlier articles, despite, say, that the later
article may be published in some obscure journal
with little reputation and the former article may
have been published in a journal with great
prestige.

It can far too often be the case that an article
suggesting, correctly, that some deeply entrenched
folk wisdom of science is just flatly wrong has to
go begging to the most mediocre of journals for page
space, at best. [In times past, the situation was
certainly even worse, as persecutions of scientists
for correctly opposing church dogma document.]

Is there any hope for a way to be put forward by
someone participating here (not by me, my knowledge
is insufficient, as are my political skills), or
adopted from elsewhere, to shed the endless rounds
of bickering, based entirely on superseded
information, which eat up so much of the meme-space
here?

I'd really like to read much more about interesting
new research here, and much less from long simmering
interpersonal feuds, science repudiated by
convincing evidence (even if not convincing to its
proponent) or kook science unsupported by evidence
convincingly (beyond the mind of the originator)
differentiating its validity from accepted science
and in its favor.

The internet already has endless venues for kook
science, one of them founded by a participant here,
and for interminable arguments (29 of them on
Usenet attributable to me).

IMWTK

xanthian.

A similar situation prevails here where persons
introducing themselves as having little knowledge,
ask questions and then spend endless rounds
of postings quarreling with or ignoring in their
responses answers furnished to their questions by
experts, while making no attempt to consult
recommended reference material.

Sigh.


[Mod. note: however accurate it may be, further meta-discussion of the
standards of posting to the group is discouraged. I can only say that
if s.a.r. was filled with professional astronomers talking to each
other about genuine research issues, nobody would be happier than
your humble servant -- mjh]

Thus spake Kent Paul Dolan
[Somewhat sorry for chopping unneeded attributions of the top
of this.]

Robert L. Oldershaw wrote:

In the Jan. 14th issue of Nature is a paper that
claims to resolve a serious problem that has
plagued the CDM cosmology for a long time.

I emphasize here the word "claims". As far as I
know, the situation is "resolves", full stop.

People who can't or won't do the math before
commenting shouldn't be casting aspersions on the
writings of those who can and do.

In this case you are wrong. The math has been done, in the form of
simulations on supercomputers (don't ask individuals to do that kind of
math), and this inconsistency in CDM is well known). It is you who
should understand the situation before making claims that it has been
resolved.

[Mod. note: perhaps references would prevent this discussion from
degenerating into contradiction -- mjh]


This is the tip of the iceberg of a larger problem.

It is indeed. A hypothesis is presented, and becomes accepted as de
facto scientific knowledge siimply because it is the first idea which
gains currency. Then problems with that hypothesis are ignored, and
alternative hypothesis are dismissed as overspeculative, although in
fact they may be no more speculative and less problematic than the first
hypothesis.

Your post is a case in point. You want to suppress discussion, although
the situation with CDM is very far from resolved.

Is there any hope for a way to be put forward by
someone participating here (not by me, my knowledge
is insufficient, as are my political skills), or
adopted from elsewhere, to shed the endless rounds
of bickering, based entirely on superseded
information, which eat up so much of the meme-space
here?


A similar situation prevails here where persons
introducing themselves as having little knowledge,
ask questions and then spend endless rounds
of postings quarreling with or ignoring in their
responses answers furnished to their questions by
experts, while making no attempt to consult
recommended reference material.

I cannot help but remark on the conflict between these two paragraphs.
You yourself profess insufficient knowledge in the one, and yet you then
take the very role which you criticise in the second.

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.rqgravity.net

"Oh No" schreef in bericht
...

In this case you are wrong. The math has been done, in the form of
simulations on supercomputers.

That is correct. However all of this is very complicated
and very difficult to evaluate if it is done correctly.

To get an idea about the software being used read this:
http://www.mpa-garching.mpg.de/galfo...get2-paper.pdf
"The cosmological simulation code GADGET-2" by Volker Springel
The above software also takes supernovae into account.
The details are at page 1109.
SPH = Smoothed Particle Hydrodynamics

For a general document about SPH simulations read this:
http://arxiv.org/PS_cache/arxiv/pdf/...001.3115v1.pdf
"Gas cooling in semi-analytic models and SPH simulations: are
results consistent?"
Specific read the introduction.
Here we read:
"In fact, lacking a 'complete theory' of star formation (as well
as of almost all the physical processes at play), we are currently not
in the position to model galaxy formation from first principles"

For a detailed document using Gadget 2 read this:
http://arxiv.org/PS_cache/arxiv/pdf/...909.0664v1.pdf
"Simulating the effect of AGN feedback on the metal enrichment of
galaxy clusters"

IMO there are two types of simulations:
1. N body simulations. A typical application is the merger of two galaxies.
2. Physical simulations. A typical application is one supernova.
Of course you can combine those two.
The problem is they are extremely complex.
For example: to study metal enrichment in a galaxy.
The easy part is that you can test your simulation because this simulation
belongs to the visible realm.
What IMO is also important that this is some sort of mixing process
i.e. the leftovers from the supernova are the building blocks
for the next generation of "heavier" stars.

In the simulation under discussion:
"Bulgeless dwarf galaxies and dark matter cores from
supernova-driven outflows" the physics involved is totally different:
the underlying concept is gas removal.
The question now becomes:
How does CDM responds to a supernova ?
Will it stay within or will it be removed from ?
IMO the simplest is a mixing process.
A removal process which results in a halo (NFW profile)
is much more complex.
See also:
http://en.wikipedia.org/wiki/Navarro...3White_profile
The extra complication is that this whole process which
involves dark matter is invisible.

For more comments see:
http://users.telenet.be/nicvroom/nat...Jan%202010.htm

Regards

--
Charles Francis

http://www.rqgravity.net

Nicolaas Vroom