Good current paper on mass / luminosity and rotation curves

http://arxiv.org/abs/1005.3154

Provides a lot of background into how Dark Matter is arrived at (as a
free parameter, whose spatial distribution is far from simple,
depending on the M/L modelled internal to the target galaxy).

David A. Smith

dlzc wrote:

http://arxiv.org/abs/1005.3154

Provides a lot of background into how Dark Matter is arrived at (as a
free parameter, whose spatial distribution is far from simple,
depending on the M/L modelled internal to the target galaxy).

David A. Smith

You do know that's not the only evidence for dark matter, right?

Dear eric gisse:

On Jun 30, 12:04*pm, eric gisse wrote:

dlzc wrote:
http://arxiv.org/abs/1005.3154

Provides a lot of background into how Dark Matter
is arrived at (as a free parameter, whose spatial
distribution is far from simple, depending on the
M/L modelled internal to the target galaxy).

You do know that's not the only evidence for dark
matter, right?

Lest we go through your list of "evidence", what you have supplied to
date can be done with simply normal matter. *If you have something
other than rotation curves (which this paper says uses M/L), or
gravitational lensing (which we both know matter alone can do, and
highly ionized "sparse" normal matter is Dark for visible light and
less energetic observations), I'd love to hear about it.

I expressed a desire to know "how it was done", and I found a paper
that describes that. *It neither agrees with me (even though it
describes an M/L-based model that needs no Dark Matter except outside
the visible disk), nor does it disagree with you. *It just drops
markers in the space I was interested in investigating. *I thought
*you* might be interested in knowing too.

As to Dark Matter:http://arxiv.org/abs/1005.4688
I wonder how you get "turbulence" with a strong Dark Matter component,
neutrinos or not?

David A. Smith

Dear eric gisse:

On Jun 30, 5:24*pm, eric gisse wrote:
dlzc wrote:
On Jun 30, 12:04 pm, eric gisse wrote:
dlzc wrote:
http://arxiv.org/abs/1005.3154

Provides a lot of background into how Dark Matter
is arrived at (as a free parameter, whose spatial
distribution is far from simple, depending on the
M/L modelled internal to the target galaxy).

You do know that's not the only evidence for dark
matter, right?

Lest we go through your list of "evidence", what you
have supplied to date can be done with simply normal
matter.

Not if you believe in electromagnetic theory. You require
some very special pleads to make bulk amounts of
hydrogen invisible, especially in *this* galaxy where radio
isn't redshifted into oblivion.

"Heliosheath". Plenty of bulk hydrogen available, and invisible until
it is braked. And we also (purportedly) are in a sparsely populated
portion of the galaxy...

If you have something
other than rotation curves (which this paper says uses M/L)

What the paper actually says is the following:

* * * * We assume that the rotation curve V(R) of the disk
galaxy, for *which we want to construct a mass model,
is known (i.e., it has *been ?observed?); as a
mathematical boundary condition, we assume that the
rotation curve remains flat at V_\infty out to infinite * * * *
* * * * radii.

They say a lot more than that. Like where they compare their results
to an actual galaxy.

Rotation curves are direct observables. The interpretation
does depend on mass to luminosity ratios, which are ALSO
observables. It isn't as if what the paper does is controversial
to your position.

It is the method used. Just as I told you.

You just have to explain how to fill in that rather substantial
amount of dark matter with normal matter while still playing
by the observed rules of electromagnetism and gravitation.

Done. Even described in that paper.

or gravitational lensing (which we both know matter alone
can do, and highly ionized "sparse" normal matter is Dark
for visible light and less energetic observations), I'd love to
hear about it.

Except normal matter isn't dark for the entire electromagnetic
spectrum. Just some of it. Like has already been discussed.

Yep. We have to have a known x-ray source behind a region, in order
to see it. Those are fairly rare.

I expressed a desire to know "how it was done", and I
found a paper that describes that. *It neither agrees with
me (even though it describes an M/L-based model that
needs no Dark Matter except outside the visible disk),

Uh, that doesn't mean as much as you think. It takes a lot
of matter to flatten out the rotation curves on the edge of a
galaxy.

*And* we can in some cases see such normal matter.

nor does it disagree with you. *It just drops
markers in the space I was interested in investigating.
*I thought *you* might be interested in knowing too.

As to Dark Matter:
http://arxiv.org/abs/1005.4688
I wonder how you get "turbulence" with a strong Dark
Matter component, neutrinos or not?

No idea. I don't run the hydrocode simulations, or study
them in sufficient detail.

Let me save you time. You cannot get turbulence without friction.
You cannot get friction with Dark Matter, even neutrinos.

David A. Smith

On 7/1/2010 4:43 AM, dlzc wrote:
Dear eric gisse:
As to Dark Matter:http://arxiv.org/abs/1005.4688
I wonder how you get "turbulence" with a strong Dark Matter component,
neutrinos or not?

David A. Smith

It would be pretty difficult to get turbulence in a "perfect fluid", as
Eric likes to keep describing Dark Matter as.

Yousuf Khan

On 6/30/2010 11:52 PM, dlzc wrote:
http://arxiv.org/abs/1005.3154

Provides a lot of background into how Dark Matter is arrived at (as a
free parameter, whose spatial distribution is far from simple,
depending on the M/L modelled internal to the target galaxy).

David A. Smith

Here was another one, a bit more basic.

[1006.2483] Dark Matter: A Primer
http://arxiv.org/abs/1006.2483

Yousuf Khan

"Yousuf Khan" wrote in message
...
| On 6/30/2010 11:52 PM, dlzc wrote:
| http://arxiv.org/abs/1005.3154
|
| Provides a lot of background into how Dark Matter is arrived at (as a
| free parameter, whose spatial distribution is far from simple,
| depending on the M/L modelled internal to the target galaxy).
|
| David A. Smith
|
| Here was another one, a bit more basic.
|
| [1006.2483] Dark Matter: A Primer
| http://arxiv.org/abs/1006.2483
|
| Yousuf Khan

"In the early 1930s, J. H. Oort found that the motion of stars in the Milky
Way hinted at the presence of far more

galactic mass than anyone had previously predicted. By studying the Doppler
shifts of stars moving near the galactic

plane, Oort was able to calculate their velocities, and thus made the
startling discovery that the stars should be

moving quickly enough to escape the gravitational pull of the luminous mass
in the galaxy. Oort postulated that

there must be more mass present within the Milky Way to hold these stars in
their observed orbits. However, Oort

noted that another possible explanation was that 85% of the light from the
galactic center was obscured by dust and

intervening matter or that the velocity measurements for the stars in
question were simply in error."

The error is indeed simple. Had Oort used emission theory his dork matter
would vanish.
Thus dork matter is the reductio-ad-absurdum of the GR conjecture.

On 6/30/10 12:52 PM, dlzc wrote:
http://arxiv.org/abs/1005.3154

Provides a lot of background into how Dark Matter is arrived at (as a
free parameter, whose spatial distribution is far from simple,
depending on the M/L modelled internal to the target galaxy).

David A. Smith

David--The case for the existence of dark matter is strong.
There is copious observational data showing way more gracvitational
influencve than can be accounted for bu baryonic matter. Background:
http://en.wikipedia.org/wiki/Dark_matter

Quoting from Ned Wright's
http://www.astro.ucla.edu/~wright/cosmology_faq.html#DM

What is the dark matter?

"When astronomers add up the masses and luminosities of the stars near
the Sun, they find that there are about 3 solar masses for every 1 solar
luminosity. When they measure the total mass of clusters of galaxies and
compare that to the total luminosity of the clusters, they find about
300 solar masses for every solar luminosity. Evidently most of the mass
in the Universe is dark. If the Universe has the critical density then
there are about 1000 solar masses for every solar luminosity, so an even
greater fraction of the Universe is dark matter. But the theory of Big
Bang nucleosynthesis says that the density of ordinary matter (anything
made from atoms) can be at most 10% of the critical density, so the
majority of the Universe does not emit light, does not scatter light,
does not absorb light, and is not even made out of atoms. It can only be
"seen" by its gravitational effects. This "non-baryonic" dark matter can
be neutrinos, if they have small masses instead of being massless, or it
can be WIMPs (Weakly Interacting Massive Particles), or it could be
primordial black holes. My nominee for the "least likely to be caught"
award goes to hypothetical stable Planck mass remnants of primordial
black holes that have evaporated due to Hawking radiation. The Hawking
radiation from the not-yet evaporated primordial black holes may be
detectable by future gamma ray telescopes, but the 20 microgram remnants
would be very hard to detect".

Sam Wormley wrote:

[...]

Put down the copy and paste for a minute.

David seems to think that dark matter doesn't exist because the jump between
galactic luminosity and stellar rotation curves is 'faulty' and that dark
matter can be, in fact, replaced by fully ionized hydrogen. Or neutral
hydrogen. The answer seems to change frequently so I'm not sure which.

If you are going to paste him stuff, paste him stuff out of an
electromagnetism textbook so he can catch up with what the rest of science
figured out a century ago.

dlzc wrote:

Dear eric gisse:

On Jun 30, 5:24 pm, eric gisse wrote:
dlzc wrote:
On Jun 30, 12:04 pm, eric gisse wrote:
dlzc wrote:
http://arxiv.org/abs/1005.3154

Provides a lot of background into how Dark Matter
is arrived at (as a free parameter, whose spatial
distribution is far from simple, depending on the
M/L modelled internal to the target galaxy).

You do know that's not the only evidence for dark
matter, right?

Lest we go through your list of "evidence", what you
have supplied to date can be done with simply normal
matter.

Not if you believe in electromagnetic theory. You require
some very special pleads to make bulk amounts of
hydrogen invisible, especially in *this* galaxy where radio
isn't redshifted into oblivion.

"Heliosheath".

A region whose density is measured in atoms per cubic meter,

Plenty of bulk hydrogen available, and invisible until
it is braked.

Unless you point a radio telescope at the 21cm line, which neutral hydrogen
radiates at. Or talk to an astronomer about the general irritant which
interstellar hydrogen poses to observations at the galactic center.

And we also (purportedly) are in a sparsely populated
portion of the galaxy...

If you have something
other than rotation curves (which this paper says uses M/L)

What the paper actually says is the following:

We assume that the rotation curve V(R) of the disk
galaxy, for which we want to construct a mass model,
is known (i.e., it has been ?observed?); as a
mathematical boundary condition, we assume that the
rotation curve remains flat at V_\infty out to infinite
radii.

They say a lot more than that. Like where they compare their results
to an actual galaxy.

What completely baffles me is your stark unwillingness to look at the
generic features of the expected rotation curves, and the observed rotation
curves. No actual discussion of how much mass is there is required.


Rotation curves are direct observables. The interpretation
does depend on mass to luminosity ratios, which are ALSO
observables. It isn't as if what the paper does is controversial
to your position.

It is the method used. Just as I told you.

Yeah, you don't like the method. Do you have an argument that isn't the
scientific equivalent of parents who think vaccines give kids autism?


You just have to explain how to fill in that rather substantial
amount of dark matter with normal matter while still playing
by the observed rules of electromagnetism and gravitation.

Done. Even described in that paper.

or gravitational lensing (which we both know matter alone
can do, and highly ionized "sparse" normal matter is Dark
for visible light and less energetic observations), I'd love to
hear about it.

Except normal matter isn't dark for the entire electromagnetic
spectrum. Just some of it. Like has already been discussed.

Yep. We have to have a known x-ray source behind a region, in order
to see it. Those are fairly rare.

Except in, once again, the bullet cluster which is lit up like a goddamn
Roetgen christmas tree. Dark matter remains dark.


I expressed a desire to know "how it was done", and I
found a paper that describes that. It neither agrees with
me (even though it describes an M/L-based model that
needs no Dark Matter except outside the visible disk),

Uh, that doesn't mean as much as you think. It takes a lot
of matter to flatten out the rotation curves on the edge of a
galaxy.

*And* we can in some cases see such normal matter.

Really, enough normal matter to completely remove the need for dark matter?


nor does it disagree with you. It just drops
markers in the space I was interested in investigating.
I thought *you* might be interested in knowing too.

As to Dark Matter:
http://arxiv.org/abs/1005.4688
I wonder how you get "turbulence" with a strong Dark
Matter component, neutrinos or not?

No idea. I don't run the hydrocode simulations, or study
them in sufficient detail.

Let me save you time. You cannot get turbulence without friction.
You cannot get friction with Dark Matter, even neutrinos.

Just a thought, but perhaps you could read the paper instead of guessing?
The turbulence specifically refers to the behavior of normal matter.


David A. Smith