Dwarf Galaxies and the Dark Web in Scientific American of March 2014

This document contains comments about the article Dwarf Galaxies and the Dark Web by Noam I. Libeskind In Scientific American of March 2014.
Small galaxies orbiting the Milky Way may have arrived via dark matter superhighways stretching across the universe. Two more articles are discussed about the same subject:
  1. Dwarf Galaxy Planes: the discovery of symmetric structures in the Local Group
  2. The rotationally stabilized VPOS and predicted proper motions of the Milky Waysatellite galaxies
  3. Reflection

"Nonsense! Hot air! Balderdash!"

Most galaxies like the Milky Way are surrounded by dozens of small galaxies that orbit around them
But these dwarf satelite galaxies do not just fly around. Instead they all sit on a thin plane, seen edge on.
This alignment comes as a surprise. Computer simulations that model how galaxies evolve have predicted that every direction in the sky should contain rouhly the same number of satelite galaxies.
A computer simulation that simulates for example the Local Cluster ie The Andomeda Galaxy and the Milky Way including Dwarf galaxies is extremely sensitive about the initial conditions.
Next we read:
Such a spherical arrangement was long thought to be a natural consequence of dark matter.
Both types of arrangements ie flat and spherical can be simulated without dark matter.
Astronomers believe dark matter pervades the univerese and plays key role in galaxy formation and expansion of the cosmos.
Astronomers think that non-baryonic matter is required to describe the Cosmic Microwave Background Radiation. Astronomers also think that non-baryonic matter is required to explain flat galaxy rotation curves. This non baryonic dark matter should than be in a halo or sphere located around the disc. The problem is when large amounts of (dark) matter are positioned in the disc than it becomes much more difficult to perform a simulation such that dwarf galaxies are also aligned in a certain direction.
Yet the puzzle of dwarf galaxy alignment has been so vexing that it has some astronomers, including Kroupa, to question whether dark matter really exists.
The issue is if you need dark matter to simulate flat galaxy rotation curves and if you include dark matter it should not be in confict with other observations.
IMO Kroupa is correct with his objections.
I was presenting a view that attempts to explain to explain the peculiar alignment of satellites by pointing to cosmic structures of darkmatter that are far larger than our Milky Way.
The problem with non-baryonic is that hugh amounts are required in the Universe at large. When you position all that non-baryonic matter at the same locations as baryonic matter than you make a rather adhoc assumption.

Missing matter

Zwicky in 1930 concluded that the coma cluster must be filled with additional unseen matter.
The problem of Zwicky in 1930 was that he assumed that galaxy masses were lower as they really are. If you increase those masses than almost no extra mass is required to make stable clusters.
in our own Milky way astronomers infer its existence from the motion of the stars on the galaxy's outskirts.
Galaxy rotation curves are flat. The primary solution is baryonic matter in planet sized objects.
Like the galaxies in the Coma cluster, these stars move too quickly to be held in by all the matter that we see.
To calculate galaxy rotation curves based what we see is shortsighted.
One way to study this evolution is through the use of computer models.
In principle correct, but should be handled with care.
Iterate this process for 13 billion years.
Don't expect you will observe anything that resembles our local universe.
Computer simulations of the cosmos have been an incredible useful way to investigate individual galaxies but they have created some notable puzzles.
Computer simulations of individual galaxies versus the cosmos are something completely different.
Computer models conclude that the pervasive dark matter in the so called halo that surrounds the Milky way should pull gas into individual clumps which should contract forming stars and dwarf galaxies ie thousands.
The problem is that dark matter is non-baryonic matter and gas baryonic matter.
The failure to find them was first identified in the 1990's and is known as the missing satellites problem
One more reason to assume that the whole problem of dark matter should be reavaluated and maybe cancelled.
Second even if small dark matter clumps do create stars those stars maybe too faint for our telescopes to see.
What is the chemical process to convert non-baryonic matter into baryonic matter?
Indeed, in the past seven years the number of stelites known to be orbiting the Milky Way has doubled.
Implying more baryonic matter, decreasing the necesity for non-baryonic mattter.
In addition the disk of the Milky Way could be blocking our view of satellite galaxies.
An argument which is in disfavour of the non-baryonic dark matter issue.
Taken together, those arguments largely settled the missing satelitte problem for most astrophysicists and saved the idea of datk matter from one of the most serious observational challenges.
It is completely the other way around. The more satellites are observed ie baryonic matter, the larger the non-baryonic dark matter problem becomes ie the less non-baryonic matter is required to make stable galaxies.

Return of the dwarf threat

For one, the stars in the satellites of the Milky way are moving far too quickly to be held together by ordinary matter alone.
It would be interesting to know how much non-baryonic is required to make theese satellites stable.
Dark matter must be holding them together just as it holds the Milky Way together.
There exists no prove for this statement. In reality the amount of missing matter in the Milky Way is small. The solution could be all available in the form of baryonic matter. Infact the more dwarf galaxies are found the amount of non-baryonic matter required decreases.

The Dark Web

Instead the computer was predicting the formation of a plane of satellites that was very close to what astronomers observe.
Such a simulation has a lot of merit. The details are interesting. How much non-baryonic matter was assumed?
"Why don't you trace the satellites back in time and see where they came from" Frenk proposed.
Such a proposal has a very low predicting value because you have to include a huge amount of dark matter which position is a gamble.
If after such a simulation the composition of the universe drastically changes you know you are on the wrong route.
If a simulation with almost no dark matter does not cause this drawback than you have made progress.
Because the Milky Way lies at a node where filaments intersect, the dwarf galaxies travel through the filaments that birthed them as they accelerated in our direction.
Next we read:
Filaments in other words serve as cosmic superhighways of dark matter.
It is the other way around: They serve as highways for baryonic matter.

Dwarf Galaxy Planes: the discovery of symmetric structures in the Local Group

By: Marcel S. Pawlowski, Pavel Kroupa, Helmut Jerjen
For a copy of this document select: http://arxiv.org/abs/1307.6210
At page 2 of this document we can read:
Under this assumption, Kroupa, modelled dark matter free MW satellite galaxies. One of these models, when compared to the Hercules satellite galaxy discovered later, turned out to be one of the few successful predictions concerning satellite galaxies
This result is very important because this implies when you perform simulations without extra matter you can imitate the reality.
Next we read:
However, later studies have focussed on comparing the Milky Way satellite galaxies to the expectations for primordial dwarf galaxies residing in dark matter sub-haloes, revealing a number of unsuccessful predictions of the Lambda CDM model.
These include the predicted central dark matter peak, the large predicted total number of satellites, the predicted existence of very concentrated, massive satellites (missing bright satellites or too big to fail problem), and the predicted internal dark matter distribution
This result is also important because it highlights how difficult it is when extra matter is included to imitate the reality.
It should be emphasised that in order to be in agreement with the state of the art 80% of all matter should be dark matter ie. non-baryonic.

The rotationally stabilized VPOS and predicted proper motions of the Milky Way satellite galaxies

By: Marcel S. Pawlowski, Pavel Kroupa
(Submitted on 4 Sep 2013)
For a copy of this document select: http://arxiv.org/abs/1309.1159
At page 2 of this document we can read:
The formation of such ancient tidal dwarf galaxies (TDGs) appears to be a most natural scenario for generating thin, planar distributions of co-orbiting dwarf galaxies etc
However, TDGs are not expected to contain significant amounts of dark matter.
TDG's contain visible baryonic matter. The question is first how much invisible baryonic matter they contain (which is difficult to answer).
However, the determination of M/L is based on the assumptions that the satellites are bound, virialized systems which is not necessarily the case, that the measured velocity dispersions are correct, and that the underlying dynamics is Newtonian which is also sometimes questioned.
The issue is partly how much gas there is within these satellites. You have to include that to determine stability investigations.
At page 9 we read:
The orbital pole distributions of dark matter sub-haloes are unable to naturally reproduce the observed clustering.
The likelihoods to reproduce the observed clustering with orbital poles drawn from tidal debris remain very high. Compared to the sub-halo hypothesis, where the likelihood drops by about an order of magnitude when updating the analysis with the higher-quality PM data, the tidal models are unaffected. This provides further support for the scenario in which the MW satellites have been born as TDGs in a past galaxy encounter.
At page 10 we read:
These comparisons indicate that the observed distribution of the orbital poles of the Milky Way satellite galaxies is extremely unlikely if they are dark matter sub-haloes as modelled in Lambda CDM simulations.
Within the observed orbital pole uncertainties it is by now rather certain that this hypothe- sis is already ruled out. More precise PM (Proper Motion) measurements, in particular for the satellite galaxies Sextans and Carina, will help to cement this verdict.
IMO this indirectly implies that the solution of flat galaxy simulations can not be found in massive non-baryonic halo's
At page 16 (Conclusion) we read:
Our analysis of the orbital poles therefore exacerbated the numerous problems which the ?CDM model has in reproducing the observed MW satellite galaxy system


In the Scientific American article Kroupa doubts if dark matter really exits after all.
In the two other documents by Kroupa et al the message is that galaxy simulations are difficult when the halo contains dwarf galaxies. The difficulty stems from two sources: To solve this conflict IMO the concept of an halo containing non-baryonic matter should be criticaly reviewed and maybe banned.
The original reason behind this halo was to simulate flat galaxy rotation curves ie. the missing matter problem. A much simpler solution for the missing matter problem is to assume, first of all, more baryonic matter in the disc.

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Created: 25 Februari 2014

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