LCDM and rotation of DM

Obvious questions, regarding other threads he

Does LCDM++ predict rotation of the DM regions or
is DM movement almost rotation free?

Would there be any way to observe rotation curves
of the DM? (Like for ordinary M, where we can see
the mass distribution but also the rotation curves?
It seems for DM not much more than the distribution
is known, correct?)

And if not directly observable, what could be the
indirect effects if DM was so to speak very
turbulent at large scales?

--
Jos

In article , Jos Bergervoet
writes:

Does LCDM++ predict rotation of the DM regions or
is DM movement almost rotation free?

The whole idea of DM is that it interacts mainly gravitationally.
Purely gravitational interactions have been studied for a long time. I
see no reason why it wouldn't rotate.

Would there be any way to observe rotation curves
of the DM?

Another whole idea of DM is that it is dark, i.e. by definition we
cannot observe it. ("Dark" is intended to indicate that it doesn't
glow, i.e. doesn't interact electromagnetically, but to many probably
implies that it is opaque, which WOULD imply an electromagnetic
interaction. "Transparent" would be a better term. "Cosmic" and "TM"
probably conjures up images of Maharishi Mahesh Yogi, though. :-) )

It seems for DM not much more than the distribution
is known, correct?

Right. And that only roughly.

In article ,
Jos Bergervoet writes:
Does LCDM++ predict rotation of the DM regions or
is DM movement almost rotation free?

The simulation movies I've seen show rotation as far as I can tell.

Would there be any way to observe rotation curves
of the DM?

I can't think how it would be possible, but lots of people are
cleverer than I am.

And if not directly observable, what could be the
indirect effects if DM was so to speak very
turbulent at large scales?

More at small scales, I think. Over large scales, angular momentum
should be near zero. Either way, dark matter motion is supposed to
be taken into account in simulations, but as I wrote in a different
thread, the physics of going from dark-matter haloes to observable
galaxies is difficult. If that physics were understood, simulations
should predict galaxy mass functions and their time evolution. I
wouldn't expect those to come out right if halo rotation is wrong,
but I'm no expert on this.

There has been quite a lot of progress on both the observational and
theoretical sides of galaxy evolution in the last 5-10 years, and I
expect we'll see a lot more in the next decade.

--
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Le 29/07/2014 09:04, Jos Bergervoet a écrit :
Obvious questions, regarding other threads he

Does LCDM++ predict rotation of the DM regions or
is DM movement almost rotation free?


Since we have NO OBSERVATIONS of this "dark matter"
there is no way to know!

Would there be any way to observe rotation curves
of the DM?

Since dark matter has never been observed, all its characteristics are
unkknown, including but not limited to, its rotation, its form, etc.

Note this:

Originally it was observed that the rotation speed in the galaxy plane
wasn't what plain gravity would predict. Dark matter would "explain" this.

But now, it has been discovered that this plane goes much further from
the galaxy center than ANYONE has ever imagined. Andromeda has a million
light year plane!

Then we have to admit that nobody knows what a galaxy is!

On 7/30/14, 1:49 AM, Phillip Helbig---undress to reply wrote:
Another whole idea of DM is that it is dark, i.e. by definition we
cannot observe it.
Wouldn't it be better to say
that we cannot observe DM with present methods
(other than gravitationally).
We cannot fall into the trap of limiting DM by our definitions.
The electromagnetic spectrum is vast(infinite).
We may be looking in the wrong place.

Richard D Saam

On 7/31/2014 10:08 AM, jacob navia wrote:
Le 29/07/2014 09:04, Jos Bergervoet a ecrit :
...
Would there be any way to observe rotation curves
of the DM?

Since dark matter has never been observed,

It has been observed gravitationally. If it
weren't for that observation, we would not
consider its existence.

.. all its characteristics are unkknown,

Its mass is known (from the above observation)
and (more indirectly) we can say its temperature
is known to be within certain limits (if you
believe the evidence for *cold* dark matter).

including but not limited to, its rotation, its form, etc.

Its rotation could (in theory) of course also
be observed gravitationally (Lense-Thirring)
but that method would not be very efficient..

... Dark matter would "explain" this.
But now, it has been discovered that this plane goes much further from
the galaxy center than ANYONE has ever imagined.

So you do admit that observations are being
made of it! (And even reliable enough ones to
force people to change previous theories.)

Andromeda has a million
light year plane!

Then we have to admit that nobody knows what a galaxy is!

Indeed, we only know 4% of it! This notion goes
with the concepts of DM and DE: there is a lot
we do not know. Perhaps you would prefer that
those two black sheep would not exist and that
we would know almost everything?

--
Jos

On Thu, 31 Jul 14, Jos Bergervoet wrote:
Indeed, we only know 4% of it! This notion goes with the concepts
of DM and DE: there is a lot we do not know. Perhaps you would
prefer that those two black sheep would not exist and that we
would know almost everything?

I think you've hit on the true definitions of DM and DE: they are
simply quantifications of how much we don't know.

Eric

Op donderdag 31 juli 2014 10:08:15 UTC+2 schreef jacob navia:
Le 29/07/2014 09:04, Jos Bergervoet a ecrit :


Would there be any way to observe rotation curves
of the DM?
IMO this a purely academic subject because galaxies completely based
on non-baryonic matter do not exist. And if they exist they are invisible

Since dark matter has never been observed, all its characteristics are
unknown, including but not limited to, its rotation, its form, etc.

One issue to explain galaxy rotation is the balance between baryonic
and non-baryonic matter.

The general argument is that if we cannot observe it (being visible)
than it should be non-baryonic.
This argument can easily be wrong because a lot of mass in a galaxy can
be baryonic and invisible. Our Earth is one example.

Note this:

Originally it was observed that the rotation speed in the galaxy plane
wasn't what plain gravity would predict. Dark matter would "explain" this.

The original idea was to explain the galaxy rotation strictly based on
what was visible. Including the observed size of the disc. As a consequence
there is a rather large discrepancy between the observed galaxy rotation
curve (based on speed/red shift) and the calculated curve based on visible
baryonic mass, which (assumed that that is all) is estimated too low.

But now, it has been discovered that this plane goes much further from
the galaxy center than ANYONE has ever imagined. Andromeda has a million
light year plane!

Do you have a reference?
When the Andromeda galaxy is much larger as previous assumed the necessity
for non-baryonic matter decreases.

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

Le 05/08/2014 07:42, Nicolaas Vroom a ecrit :
But now, it has been discovered that this plane goes much further from
the galaxy center than ANYONE has ever imagined. Andromeda has a million
light year plane!
Do you have a reference?

http://arxiv.org/abs/1301.0446
A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda
Galaxy

From the abstract:
"The structure is vast: at least 400 kpc in diameter, but also extremely
thin, with a perpendicular scatter 14.1 kpc (99% confidence)."

400 000 parsecs -- * 3.26 -- 1 304 000 light years

Le 07/08/2014 08:14, jacob navia a écrit :
Le 05/08/2014 07:42, Nicolaas Vroom a ecrit :
But now, it has been discovered that this plane goes much further from
the galaxy center than ANYONE has ever imagined. Andromeda has a million
light year plane!
Do you have a reference?

http://arxiv.org/abs/1301.0446
A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda
Galaxy

From the abstract:
"The structure is vast: at least 400 kpc in diameter, but also extremely
thin, with a perpendicular scatter 14.1 kpc (99% confidence)."

400 000 parsecs -- * 3.26 -- 1 304 000 light years


How can this thin disk have formed?

Note that the satellite galaxies at 150 Kpc have a rotation period of 5
Gy! Five BILLION years for just 1 period.

To made a such thin disk MANY rotation periods are needed, much more
than the ~2.7 periods BB theory postulates as the "Age of the Universe"
(13.7 Gy).

[Mod. note: please try to justify statements like this -- mjh]

Besides, the geometry of that plane and the Milky Way plane (that is
also huge) are almost perpendicular (83 degrees). Is this a coincidence?

A group of astronomers have used the Sloan Survey to find out that
thousands of galaxies have this pattern and that the Milky Way and
Andromeda are NOT exceptions but they show us a rule! See for a reference:

Neil G. Ibata, Rodrigo A. Ibata, Benoit Famaey, Geraint F. Lewis.
Velocity anti-correlation of diametrically opposed galaxy satellites in
the low-redshift Universe. Nature, 2014; DOI: 10.1038/nature13481

also available at http://xxx.lanl.gov/abs/1407.8178

In the abstract, the authors say:

Recent work has shown that both the Milky Way and the Andromeda galaxies
possess the unexpected property that their dwarf satellite galaxies are
aligned in thin and kinematically coherent planar structures. It is now
important to evaluate the incidence of such planar structures in the
larger galactic population, since the Local Group may not be a
sufficiently representative environment. Here we report that the
measurement of the velocity of pairs of diametrically opposed galaxy
satellites provides a means to determine statistically the prevalence of
kinematically coherent planar alignments. In the local universe
(redshift z0.05), we find that such satellite pairs out to a
galactocentric distance of 150 kpc are preferentially anti-correlated in
their velocities (99.994% confidence level), and that the distribution
of galaxies in the larger scale environment (beyond 150 kpc and up to ~2
Mpc) is strongly elongated along the axis joining the inner satellite
pair (7sigma confidence). Our finding may indicate that co-rotating
planes of satellites, similar to that seen around the Andromeda galaxy,
are ubiquitous in nature, while their coherent motion also suggests that
they are a significant repository of angular momentum on ~100 kpc scales.