Galaxy study hints at cracks in dark matter theories
Yousuf Khan
September 2009 - New Scientist
"Since dark matter does not radiate light, astronomers infer its
distribution by looking at how a galaxy's gas and stars are moving.
Previous studies have suggested that dark matter must be uniformly
distributed within a galaxy's central region � a confounding result
since the dark matter's gravity should make it progressively denser
towards a galaxy's centre.
Now, the tale has taken a deeper turn into the unknown, thanks to an
analysis of the normal matter at the centres of 28 galaxies of all
shapes and sizes. The study shows that there is always five times more
dark matter than normal matter where the dark matter density has dropped
to one-quarter of its central value."
http://www.newscientist.com/article/dn17892-galaxy-study-hints-at-cracks-in-dark-matter-theories.html?DCMP=OTC-rss&nsref=online-news
eric gisse
> Galaxy study hints at cracks in dark matter theories - space - 30
> September 2009 - New Scientist
> "Since dark matter does not radiate light, astronomers infer its
> distribution by looking at how a galaxy's gas and stars are moving.
> Previous studies have suggested that dark matter must be uniformly
> distributed within a galaxy's central region ? a confounding result
> since the dark matter's gravity should make it progressively denser
> towards a galaxy's centre.
Why?
Remember kids - no electromagnetic dissipative forces means angular momentum
stays where it is. Hard to collapse a cloud of noninteracting material.
>
> Now, the tale has taken a deeper turn into the unknown, thanks to an
> analysis of the normal matter at the centres of 28 galaxies of all
> shapes and sizes. The study shows that there is always five times more
> dark matter than normal matter where the dark matter density has dropped
> to one-quarter of its central value."
Interesting, but its' meaning is fuzzy to me. Ok, so there's an unexpected
correlation between densities of dark and baryonic matter. What now?
> http://www.newscientist.com/article/dn17892-galaxy-study-hints-at-cracks-
in-dark-matter-theories.html?DCMP=OTC-rss&nsref=online-news
N:dlzc D:aol T:com (dlzc)
"Yousuf Khan" <bbb...@spammenot.yahoo.com> wrote in message
news:4ac3e1d5$1...@news.bnb-lp.com...
> Galaxy study hints at cracks in dark matter theories - space -
> 30 September 2009 - New Scientist
> "Since dark matter does not radiate light, astronomers
> infer its distribution by looking at how a galaxy's gas
> and stars are moving. Previous studies have suggested
> that dark matter must be uniformly distributed within a
> galaxy's central region �
No this is not correct. Both microlensing and galactic motion
show the Dark Matter's "uniform distribution" to be near zero at
the center, to a maximum near the rim, and then peter out beyond
the rim. For spiral galaxies.
> a confounding result since the dark matter's gravity
> should make it progressively denser towards a galaxy's
> centre.
Completely incorrect.
> Now, the tale has taken a deeper turn into the unknown,
> thanks to an analysis of the normal matter at the centres
> of 28 galaxies of all shapes and sizes. The study shows
> that there is always five times more dark matter than
> normal matter where the dark matter density has dropped to
> one-quarter of its central value."
> http://www.newscientist.com/article/dn17892-galaxy-study-hints-at-cracks-in-dark-matter-theories.html?DCMP=OTC-rss&nsref=online-news
Sounds OK. No surprises, despite the author's lack of correct
information.
David A. Smith
Uncle Al
>
> Yousuf Khan wrote:
>
> > Galaxy study hints at cracks in dark matter theories - space - 30
> > September 2009 - New Scientist
> > "Since dark matter does not radiate light, astronomers infer its
> > distribution by looking at how a galaxy's gas and stars are moving.
> > Previous studies have suggested that dark matter must be uniformly
> > distributed within a galaxy's central region ? a confounding result
> > since the dark matter's gravity should make it progressively denser
> > towards a galaxy's centre.
>
> Why?
>
> Remember kids - no electromagnetic dissipative forces means angular momentum
> stays where it is. Hard to collapse a cloud of noninteracting material.
One would expect density gradient stacking as with atmospheric density
vs. altitude. Heating the atmosphere doesn't make it homogeneous with
altitude, it alters scale. GR treatments of on-interacting dust
ditto.
If the density did not vary with radius (gravitational height) as
above, what prevents the dark matter distribution from homogeneously
extending to infinity? Nothing. The trick is to get a spherical
distribution like stars in a globular cluster, not another disk.
Dark matter is curve fitting. Its properties other than gravitation
are obscene. Then we have the Bullet Nebula...
> > Now, the tale has taken a deeper turn into the unknown, thanks to an
> > analysis of the normal matter at the centres of 28 galaxies of all
> > shapes and sizes. The study shows that there is always five times more
> > dark matter than normal matter where the dark matter density has dropped
> > to one-quarter of its central value."
>
> Interesting, but its' meaning is fuzzy to me. Ok, so there's an unexpected
> correlation between densities of dark and baryonic matter. What now?
>
> > http://www.newscientist.com/article/dn17892-galaxy-study-hints-at-cracks-
> in-dark-matter-theories.html?DCMP=OTC-rss&nsref=online-news
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/lajos.htm#a2
Yousuf Khan
> "Yousuf Khan" <bbb...@spammenot.yahoo.com> wrote in message
> news:4ac3e1d5$1...@news.bnb-lp.com...
>> thanks to an analysis of the normal matter at the centres
>> of 28 galaxies of all shapes and sizes. The study shows
>> that there is always five times more dark matter than
>> normal matter where the dark matter density has dropped to
>> one-quarter of its central value."
>> http://www.newscientist.com/article/dn17892-galaxy-study-hints-at-cracks-in-dark-matter-theories.html?DCMP=OTC-rss&nsref=online-news
>
> Sounds OK. No surprises, despite the author's lack of correct
> information.
>
> David A. Smith
Here's another article about it, might be less sensationalist:
St Andrews scientists find mysterious dark matter link | Scotland | STV News
"Now the St Andrews team believe that the interactions between dark and
ordinary matter could be more important and more complex than previously
thought. They have even speculated that dark matter might not exist and
that the strange motions of stars in galaxies are due to a change in
gravity.
Dr. Zhao said: "The pattern that the data reveal is extremely odd. It�s
like finding a zoo of animals of all ages and sizes miraculously having
identical, say, weight in their backbones or something.
"It is possible that a non-gravitational fifth force is ruling the dark
matter with an invisible hand, leaving the same fingerprints on all
galaxies, irrespective of their ages, shapes and sizes.�"
http://news.stv.tv/scotland/126875-st-andrews-scientists-find-mysterious-dark-matter-link/
>> Galaxy study hints at cracks in dark matter theories - space -
>> 30 September 2009 - New Scientist
>> "Since dark matter does not radiate light, astronomers
>> infer its distribution by looking at how a galaxy's gas
>> and stars are moving. Previous studies have suggested
>> that dark matter must be uniformly distributed within a
>> galaxy's central region �
>
> No this is not correct. Both microlensing and galactic motion
> show the Dark Matter's "uniform distribution" to be near zero at
> the center, to a maximum near the rim, and then peter out beyond
> the rim. For spiral galaxies.
This brings up something that I've been mulling about in my head
recently. Is it possible that we're now seeing a breakdown in the
symmetry of gravity? We know early in the formation of the Universe, all
forces were united and symmetrical. Then a few billionths of a second
later, they were breaking symmetry step-by-step into the four forces we
know now: Gravity, Electromagnetism, Strong & Weak Nuclear. As the
Universe cools, could we be witnessing the force of Gravity further
breaking down into two new forces?
The symmetry breakdown could be dependent on the density of the matter
around it. That might be why we see no effects of Dark Matter in the
confines of a Solar system, because the density of matter is above a
certain limit. The same case might hold true inside the confines of the
galactic bulge near the galactic black hole. It's only in the outer
reaches where star densities become small that we see the effects of
Dark Matter. Then when the densities of matter get even smaller, such as
in the entire cosmos as a whole, we start seeing the effects of Dark
Energy. Newton-Einstein gravity breaks down into Dark Matter-style and
Dark Energy-style gravity with change of the density levels.
Yousuf Khan
john
> N:dlzc D:aol T:com (dlzc) wrote:
>
> > "Yousuf Khan" <bbb...@spammenot.yahoo.com> wrote in message
> >news:4ac3e1d5$1...@news.bnb-lp.com...
> >> Now, the tale has taken a deeper turn into the unknown,
> >> thanks to an analysis of the normal matter at the centres
> >> of 28 galaxies of all shapes and sizes. The study shows
> >> that there is always five times more dark matter than
> >> normal matter where the dark matter density has dropped to
> >> one-quarter of its central value."
>
> > Sounds OK. No surprises, despite the author's lack of correct
> > information.
>
> > David A. Smith
>
> Here's another article about it, might be less sensationalist:
>
> St Andrews scientists find mysterious dark matter link | Scotland | STV News
> "Now the St Andrews team believe that the interactions between dark and
> ordinary matter could be more important and more complex than previously
> thought. They have even speculated that dark matter might not exist and
> that the strange motions of stars in galaxies are due to a change in
> gravity.
>
> like finding a zoo of animals of all ages and sizes miraculously having
> identical, say, weight in their backbones or something.
>
> "It is possible that a non-gravitational fifth force is ruling the dark
> matter with an invisible hand, leaving the same fingerprints on all
>
> >> Galaxy study hints at cracks in dark matter theories - space -
> >> 30 September 2009 - New Scientist
> >> "Since dark matter does not radiate light, astronomers
> >> infer its distribution by looking at how a galaxy's gas
> >> and stars are moving. Previous studies have suggested
> >> that dark matter must be uniformly distributed within a
> >
> > No this is not correct. Both microlensing and galactic motion
> > show the Dark Matter's "uniform distribution" to be near zero at
> > the center, to a maximum near the rim, and then peter out beyond
> > the rim. For spiral galaxies.
>
> This brings up something that I've been mulling about in my head
> recently. Is it possible that we're now seeing a breakdown in the
> symmetry of gravity? We know early in the formation of the Universe, all
> forces were united and symmetrical. Then a few billionths of a second
> later, they were breaking symmetry step-by-step into the four forces we
> know now: Gravity, Electromagnetism, Strong & Weak Nuclear. As the
> Universe cools, could we be witnessing the force of Gravity further
> breaking down into two new forces?
>
> The symmetry breakdown could be dependent on the density of the matter
> around it. That might be why we see no effects of Dark Matter in the
> confines of a Solar system, because the density of matter is above a
> certain limit. The same case might hold true inside the confines of the
> galactic bulge near the galactic black hole. It's only in the outer
> reaches where star densities become small that we see the effects of
> Dark Matter. Then when the densities of matter get even smaller, such as
> in the entire cosmos as a whole, we start seeing the effects of Dark
> Energy. Newton-Einstein gravity breaks down into Dark Matter-style and
> Dark Energy-style gravity with change of the density levels.
>
> Yousuf Khan
Matter creates gravity only in a secondary way, by
absorbing incoming energy.
Lesage was right.
It's just a matter of identifying the nature of
the incoming energy and why it is absorbed
by matter.
john
dlzc
On Sep 30, 9:24 pm, Yousuf Khan <bbb...@spammenot.yahoo.com> wrote:
> N:dlzcD:aol T:com (dlzc) wrote:
>
> > "Yousuf Khan" <bbb...@spammenot.yahoo.com> wrote in message
> >news:4ac3e1d5$1...@news.bnb-lp.com...
> >> Now, the tale has taken a deeper turn into the unknown,
> >> thanks to an analysis of the normal matter at the centres
> >> of 28 galaxies of all shapes and sizes. The study shows
> >> that there is always five times more dark matter than
> >> normal matter where the dark matter density has dropped to
> >> one-quarter of its central value."
<snip link now broken by Google.Groups>
>
> > Sounds OK. No surprises, despite the author's lack of
> > correct information.
>
> Here's another article about it, might be less sensationalist:
>
> St Andrews scientists find mysterious dark matter link |
> Scotland | STV News "Now the St Andrews team believe
> that the interactions between dark and ordinary matter
> could be more important and more complex than
> previously thought. They have even speculated that dark
> matter might not exist and that the strange motions of
> stars in galaxies are due to a change in gravity.
Still sensationalist, and likely correct IMO.
> Dr. Zhao said: "The pattern that the data reveal is
> extremely odd. It’s like finding a zoo of animals of all
> ages and sizes miraculously having identical, say,
> weight in their backbones or something.
>
> "It is possible that a non-gravitational fifth force is
> ruling the dark matter with an invisible hand, leaving
> the same fingerprints on all galaxies, irrespective of
> their ages, shapes and sizes.
<snip another link broken by Google.Groups>
Well, as the Universe cools, it should be expected that new forces
will come into sway.
> >> Galaxy study hints at cracks in dark matter
> >> theories - space - 30 September 2009 - New
> >> Scientist "Since dark matter does not radiate
> >> light, astronomers infer its distribution by
> >> looking at how a galaxy's gas and stars are
> >> moving. Previous studies have suggested
> >> that dark matter must be uniformly distributed
> >> within a galaxy's central region –
> >
> > No this is not correct. Both microlensing and
> > galactic motion show the Dark Matter's "uniform
> > distribution" to be near zero at the center, to a
> > maximum near the rim, and then peter out beyond
> > the rim. For spiral galaxies.
>
> This brings up something that I've been mulling
> about in my head recently. Is it possible that we're
> now seeing a breakdown in the symmetry of gravity?
Possibly. The anomalous motion of spiral galaxies extends as far back
as there are spiral galaxies. So the "breakage" has existed for 11 Gy
or so. And (inflation and) expansion existed back even then.
> We know early in the formation of the Universe,
> all forces were united and symmetrical.
"Know" is a bit strong. It makes sense that it would be that way, to
a race that has never left their solar system...
> Then a few billionths of a second later, they
> were breaking symmetry step-by-step into the four
> forces we know now: Gravity, Electromagnetism,
> Strong & Weak Nuclear. As the Universe cools,
> could we be witnessing the force of Gravity further
> breaking down into two new forces?
Well, no, since gravity is not a force. But we could certainly be
witnessing some new effect.
> The symmetry breakdown could be dependent
> on the density of the matter around it.
Probably more like the energy or momentum density...
> That might be why we see no effects of Dark
> Matter in the confines of a Solar system,
... yet ...
> because the density of matter is above a
> certain limit.
Well, we *are* looking for non-gravitational interactions when we are
looking for Dark Matter. So in all fairness, we are looking for
things that Dark Matter absolutely cannot do / be, and agree with all
the things it was proposed to describe. Like certain kooks that
insist that light must have mass... we look under a streetlight for a
lost object, because it is too dark to find the object elsewhere. How
in the world do you detect an effect that is 40 something orders of
magnitude less than the next weakest, and then differentiate that
effect from something like a neutrino or neutron?
> The same case might hold true inside the confines
> of the galactic bulge near the galactic black hole.
> It's only in the outer reaches where star densities
> become small that we see the effects of Dark
> Matter.
Which is, essentially, MOND's proposition.
> Then when the densities of matter get even smaller,
> such as in the entire cosmos as a whole, we start
> seeing the effects of Dark Energy. Newton-Einstein
> gravity breaks down into Dark Matter-style and
> Dark Energy-style gravity with change of the density
> levels.
See, I don't see it like that. The cosmological constant does not
express only at certain scales. It might be essentially undetectable
at small scales, but it should be detectable in things as large as a
galaxy. Yet Dark Energy only expresses at scales larger than our
supercluster, and is seen to be then... uniform in all directions.
This "artifact" could simply be our resolution in establishing
expansion. But right now, it seems to me this makes Dark Energy some
pretty odd stuff, either that or we are in a "special place" again.
David A. Smith
Steve Willner
"N:dlzc D:aol T:com \(dlzc\)" <dl...@cox.net> writes:
> Both microlensing and galactic motion
> show the Dark Matter's "uniform distribution" to be near zero at
> the center, to a maximum near the rim, and then peter out beyond
> the rim. For spiral galaxies.
Could you please cite a source for that? The _ratio_ of dark matter
to luminous matter goes up with radius, but I've never seen anything
suggesting the dark matter density itself goes up. You might want to
see http://burro.cwru.edu/JavaLab/RotcurveWeb/main_BACK.html
(and related pages on the site, which is excellent).
> > a confounding result since the dark matter's gravity
> > should make it progressively denser towards a galaxy's
> > centre.
>
> Completely incorrect.
Why do you think the expectation is incorrect?
> > The study shows
> > that there is always five times more dark matter than
> > normal matter where the dark matter density has dropped to
> > one-quarter of its central value."
> > http://www.newscientist.com/article/dn17892-galaxy-study-hints-at-cracks-in-dark-matter-theories.html?DCMP=OTC-rss&nsref=online-news
Can anyone supply a reference for the actual article or preprint?
It's impossible to tell much from press releases. (Yousuf: this is a
general request. Many of the articles you summarize could be
interesting, but there's no way to tell what they are really saying
without seeing the actual article. Even giving the author names
would let other people look up the article itself.)
--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swil...@cfa.harvard.edu
Cambridge, MA 02138 USA
dlzc
On Oct 1, 10:42 am, will...@cfa.harvard.edu (Steve Willner) wrote:
> In article <sVSwm.12240$Fg7.11...@newsfe03.iad>,
> "N:dlzcD:aol T:com \(dlzc\)" <dl...@cox.net> writes:
>
> > Both microlensing and galactic motion
> > show the Dark Matter's "uniform distribution" to be
> > near zero at the center, to a maximum near the rim,
> > and then peter out beyond the rim. For spiral
> > galaxies.
>
> Could you please cite a source for that?
Before I start searching, Dark Matter was proposed to "correct" the
rotation of spiral galaxies so that the outer rim could "spin" as fast
as was seen, given the visble matter near the core's rotation. If you
place more Dark Matter at the center, then you have an anomalously
slow central rotation.
http://arxiv.org/abs/astro-ph/0110390
... and I suspect this just confirms the distribution you were
expecting.
> The _ratio_ of dark matter to luminous matter goes
> up with radius, but I've never seen anything
> suggesting the dark matter density itself goes up.
I don't see how you can have the first part of the sentence without
the second. Besides my claim was against dDM / dr... which is not
really a density...
> You might want to see
http://burro.cwru.edu/JavaLab/RotcurveWeb/main_BACK.html
> (and related pages on the site, which is excellent).
OK.
> > > a confounding result since the dark matter's
> > > gravity should make it progressively denser
> > > towards a galaxy's centre.
>
> > Completely incorrect.
>
> Why do you think the expectation is incorrect?
Dark Matter only interacts via gravitation. Therefore is cannot
"coalesece" towards a center... only move (on average) faster when it
is there. This does not provide "density".
David A. Smith
Yousuf Khan
> Can anyone supply a reference for the actual article or preprint?
> It's impossible to tell much from press releases. (Yousuf: this is a
> general request. Many of the articles you summarize could be
> interesting, but there's no way to tell what they are really saying
> without seeing the actual article. Even giving the author names
> would let other people look up the article itself.)
>
Well, it mentions this at the bottom of the second article:
Journal reference: Nature (vol 461, p 627)
Yousuf Khan
Steve Willner
dlzc <dl...@cox.net> writes:
> Before I start searching, Dark Matter was proposed to "correct" the
> rotation of spiral galaxies so that the outer rim could "spin" as fast
> as was seen, given the visble matter near the core's rotation.
Galaxy rotation curves are the most relevant evidence for this
discussion, but historically the first suggestion of dark matter (by
Fritz Zwicky in the 1930's) was based on galaxy velocity dispersions
in clusters.
> If you place more Dark Matter at the center, then you have an
> anomalously slow central rotation.
If you ignore the luminous matter and assume a spherical
distribution, a flat rotation curve requires density to go inversely
as radius squared.
> http://arxiv.org/abs/astro-ph/0110390
I'm not sure of the relevance of this.
> >=A0The _ratio_ of dark matter to luminous matter goes
> > up with radius, but I've never seen anything
> > suggesting the dark matter density itself goes up.
>
> I don't see how you can have the first part of the sentence without
> the second.
The density of luminous matter goes down _faster_ than the density of
dark matter does. Galaxy disks are exponential.
> Besides my claim was against dDM / dr... which is not
> really a density...
I don't understand that, but I'll repeat my recommendation of
http://burro.cwru.edu/JavaLab/RotcurveWeb/main_BACK.html
> Dark Matter only interacts via gravitation. Therefore is cannot
> "coalesece" towards a center... only move (on average) faster when it
> is there. This does not provide "density".
Density is mass per unit volume, and I'm not sure what "coalesce" has
to do with anything. A self-gravitating system will normally have
higher density at its center. Globular star clusters provide a good
example. The stars interact (essentially) only by gravity
(collisions being very rare indeed), yet the density is highest in
the center. Dark matter -- we think -- acts the same way.
You might also want to have a look at the cosmological dark matter
simulations such as
http://www.mpa-garching.mpg.de/galform/millennium/
These show structure forming and density perturbations growing with
time, and only gravity is involved. Then add in that galaxies form
at dark-matter density peaks, and you can see that dark matter
density in galaxies will be highest at the centers. (I'm leaving out
complications such as galaxy interactions, e.g. Bullet Cluster.)
Sam Wormley
> Matter creates gravity only in a secondary way, by
> absorbing incoming energy.
> Lesage was right.
Le Sage's theory of gravitation
http://en.wikipedia.org/wiki/Le_Sage's_theory_of_gravitation
"The re-examination of Le Sage's theory in the 19th century identified
several closely interconnected problems with the theory. These relate
to excessive heating, frictional drag, shielding, and gravitational
aberration. The recognition of these problems, in conjunction with a
general shift away from mechanical based theories, resulted in a
progressive loss of interest in Le Sage’s theory. Ultimately in the
twentieth century Le Sage’s theory was eclipsed by Einstein’s theory
of general relativity".
N:dlzc D:aol T:com (dlzc)
"Steve Willner" <wil...@cfa.harvard.edu> wrote in message
news:ha5sga$4f8$1...@news.eternal-september.org...
> In article
> <921078ea-9473-47e1...@u16g2000pru.googlegroups.com>,
> dlzc <dl...@cox.net> writes:
>> Before I start searching, Dark Matter was proposed to
>> "correct" the rotation of spiral galaxies so that the outer
>> rim could "spin" as fast as was seen, given the visble
>> matter near the core's rotation.
>
> Galaxy rotation curves are the most relevant evidence
> for this discussion, but historically the first suggestion
> of dark matter (by Fritz Zwicky in the 1930's) was based
> on galaxy velocity dispersions in clusters.
Cool. Thanks!
>> If you place more Dark Matter at the center, then you
>> have an anomalously slow central rotation.
>
> If you ignore the luminous matter and assume a spherical
> distribution, a flat rotation curve requires density to go
> inversely as radius squared.
For a constant V, MG/r is constant, rho is M / (4/3*pi*r^3),
which gives the product of M and r^2 as a constant. Agreed. But
I am less interested in density than total mass, and within what
distance that mass is located.
>> http://arxiv.org/abs/astro-ph/0110390
>
> I'm not sure of the relevance of this.
You asked what I thought the distribution was.
>> > The _ratio_ of dark matter to luminous matter goes
>> > up with radius, but I've never seen anything
>> > suggesting the dark matter density itself goes up.
>>
>> I don't see how you can have the first part of the sentence
>> without the second.
>
> The density of luminous matter goes down _faster_ than
> the density of dark matter does. Galaxy disks are
> exponential.
Again, my question is the total mass within a given radius. And
how that mass is distributed radially, not "volumetrically".
>> Besides my claim was against dDM / dr... which is not
>> really a density...
>
> I don't understand that, but I'll repeat my recommendation of
> http://burro.cwru.edu/JavaLab/RotcurveWeb/main_BACK.html
Which is still not speaking to this...
>> Dark Matter only interacts via gravitation. Therefore is
>> cannot "coalesece" towards a center... only move (on
>> average) faster when it is there. This does not provide
>> "density".
>
> Density is mass per unit volume, and I'm not sure what
> "coalesce" has to do with anything.
You keep saying more DM is located at the center. This requires
"coalescence".
> A self-gravitating system will normally have higher density
> at its center.
Why? Because of "tidally-driven friction"? Won't work with Dark
Matter.
> Globular star clusters provide a good example. The
> stars interact (essentially) only by gravity (collisions
> being very rare indeed), yet the density is highest in
> the center. Dark matter -- we think -- acts the same way.
Dark Matter as "stuff", had to have an average velocity that
would allow it to be restrained by the gravity of the particular
galactic disk. If it were truly "cold", it could be distributed
as you say. But it would eventually be gravitationally "boosted"
to have the same galactic-centric angular momentum as the rest of
the disk, with no particular requirement to stay along the
ecliptic (no friction to force "averaging"). This would force it
to spend more time "outside", and to "shoot through the middle"
quicker. Yielding a lower "density" where speed is highest (in
Bernoulli fashion).
> You might also want to have a look at the cosmological
> dark matter simulations such as
> http://www.mpa-garching.mpg.de/galform/millennium/
>
> These show structure forming and density perturbations
> growing with time, and only gravity is involved. Then add
> in that galaxies form at dark-matter density peaks, and
> you can see that dark matter density in galaxies will be
> highest at the centers. (I'm leaving out complications
> such as galaxy interactions, e.g. Bullet Cluster.)
I'll review it.
David A. Smith
Steve Willner
Close, but it should be (MG/r)^0.5 that's constant.
> rho is M / (4/3*pi*r^3),
> which gives the product of M and r^2 as a constant.
So flat rotation curve implies total mass goes as r and mass density
goes as r^-2. That's for a spherically-symmetric mass distribution,
of course.
> I am less interested in density than total mass, and within what
> distance that mass is located.
If you have density, you can integrate to get total mass.
> Again, my question is the total mass within a given radius. And
> how that mass is distributed radially, not "volumetrically".
See above; total mass increases linearly with r. Mass in each thin
shell of fixed thickness is constant. Of course for real galaxies,
at large enough radius the dark matter density declines faster than
r^-2 (or something else happens such as non-sphericity becoming
important), but that's outside the visible matter.
> You keep saying more DM is located at the center. This requires
> "coalescence".
Define "coalescence." If it means "concentration," then of course
you have simply restated the assertion. If it implies non-
gravitational interactions, then the examples of globular clusters
and of flat rotation curves proves the second statement is
incorrect.
> > A self-gravitating system will normally have higher density
> > at its center.
>
> Why? Because of "tidally-driven friction"? Won't work with Dark
> Matter.
Tidal friction (more commonly known as "dynamical friction") is
purely gravitational. Why do you think it won't work for dark
matter?
> Dark Matter as "stuff", had to have an average velocity that
> would allow it to be restrained by the gravity of the particular
> galactic disk. If it were truly "cold", it could be distributed
> as you say. But it would eventually be gravitationally "boosted"
> to have the same galactic-centric angular momentum as the rest of
> the disk, with no particular requirement to stay along the
> ecliptic (no friction to force "averaging"). This would force it
> to spend more time "outside", and to "shoot through the middle"
> quicker. Yielding a lower "density" where speed is highest (in
> Bernoulli fashion).
I don't understand this argument at all, but again I refer you to
globular clusters. (I agree that, in a closed system at equilibrium,
dark matter will have the same angular momentum per unit mass as
whatever it's interacting with.)
I think you need to take a more careful look at the references I
suggested in earlier posts.
(Yousuf: thanks for the _Nature_ reference. I have the paper now but
haven't read it yet.)
N:dlzc D:aol T:com (dlzc)
"Steve Willner" <wil...@cfa.harvard.edu> wrote in message
news:hadlnb$6sj$1...@news.eternal-september.org...
> In article <i5zxm.26466$Bl2....@newsfe14.iad>,
> "N:dlzc D:aol T:com \(dlzc\)" <dl...@cox.net> writes:
>> For a constant V, MG/r is constant,
>
> Close, but it should be (MG/r)^0.5 that's constant.
Which trivially reduces MG/r being constant.
>> rho is M / (4/3*pi*r^3),
>> which gives the product of M and r^2 as a constant.
>
> So flat rotation curve implies total mass goes as r and
> mass density goes as r^-2. That's for a spherically-
> symmetric mass distribution, of course.
Which caveat is less necessary if you do not abstract to density.
>> I am less interested in density than total mass, and
>> within what distance that mass is located.
>
> If you have density, you can integrate to get total mass.
Not quite. You'd need density as a function of r, theta and phi
too.
>> Again, my question is the total mass within a given
>> radius. And how that mass is distributed radially, not
>> "volumetrically".
>
> See above; total mass increases linearly with r. Mass
> in each thin shell of fixed thickness is constant. Of
> course for real galaxies, at large enough radius the
> dark matter density declines faster than r^-2 (or
> something else happens such as non-sphericity becoming
> important), but that's outside the visible matter.
Yet it is still observable in certain cases, via microlensing...
>> You keep saying more DM is located at the center. This
>> requires "coalescence".
>
> Define "coalescence." If it means "concentration," then
> of course you have simply restated the assertion.
No I mean the system had to start out with a "lump" in Dark
Matter, or Dark Matter somehow can disspate energy / momentum
other than gravitationally.
Or there is no central concentration of Dark Matter, as you keep
saying.
> If it implies non- gravitational interactions, then the
> examples of globular clusters and of flat rotation curves
> proves the second statement is incorrect.
I don't see it as my problem, as I am not the one asserting it.
I just keep pointing out there is no mechanism to attain it and
you are agreeing.
>> > A self-gravitating system will normally have higher density
>> > at its center.
>>
>> Why? Because of "tidally-driven friction"? Won't work
>> with Dark Matter.
>
> Tidal friction (more commonly known as "dynamical friction") is
> purely gravitational. Why do you think it won't work for dark
> matter?
Conservation of energy. Since there are no losses with Dark
Matter, *energy* (not just momentum) must be conserved.
>> Dark Matter as "stuff", had to have an average velocity that
>> would allow it to be restrained by the gravity of the
>> particular
>> galactic disk. If it were truly "cold", it could be
>> distributed
>> as you say. But it would eventually be gravitationally
>> "boosted"
>> to have the same galactic-centric angular momentum as the
>> rest of the disk, with no particular requirement to stay along
>> the ecliptic (no friction to force "averaging"). This would
>> force
>> it to spend more time "outside", and to "shoot through the
>> middle" quicker. Yielding a lower "density" where speed is
>> highest (in Bernoulli fashion).
>
> I don't understand this argument at all, but again I refer you
> to globular clusters.
Which have Dark Matter and it too was ejected along with the
stars.
> (I agree that, in a closed system at equilibrium, dark matter
> will have the same angular momentum per unit mass as
> whatever it's interacting with.)
>
> I think you need to take a more careful look at the references
> I
> suggested in earlier posts.
I have, but if this is the best you've got, we can be done. It
seems to be not addressing what you think it does, or I am too
block headed to see it.
David A. Smith
Steve Willner
"N:dlzc D:aol T:com \(dlzc\)" <dl...@cox.net> writes:
> No I mean the system had to start out with a "lump" in Dark
> Matter, or Dark Matter somehow can disspate energy / momentum
> other than gravitationally.
You have yourself demonstrated that flat rotation curves imply mass
density is highest in the center. If you think that violates
physics, it should be a clue that something is wrong.
SW> Tidal friction (more commonly known as "dynamical friction") is
SW> purely gravitational. Why do you think it won't work for dark
SW> matter?
> Conservation of energy. Since there are no losses with Dark
> Matter, *energy* (not just momentum) must be conserved.
Yes. Dynamical friction conserves energy. Why do you think
otherwise? Perhaps the name is misleading, but dynamical friction
involves pure, collisionless, Newtonian gravity. Look at the buildup
of structure in the Millennium simulation. Energy is being
conserved, but ordered bulk motion is being converted to random
motion. That leads to structures with central mass concentrations.
Galaxy collisions are another example. The colliding galaxies merge
but "puff up," i.e., the velocity dispersion of the final galaxy is
much larger than the velocity dispersion of the original ones.
A quick web search didn't turn up a good description of dynamical
friction. The Wikipedia article looks basically correct but is
rudimentary. Perhaps a more extensive search would find something
better.
john
Sam, DM is a problem.
Singularities is a problem.
Movement of electrons without requiring energy is a problem.
Movement of photons without losing energy is a problem.
Galactic rotation curves is a problem.
Protons that never degrade is a problem.
Protons exactly the same size everywhere is a problem.
You call photons mechanical?
john
Sam Wormley
>
>
> Sam, DM is a problem.
John, Why to you think that Matter (lot's of it), that doesn't
interact electromagnetically, is a problem? There are particles
like that. Neutrinos come to mind.
> Singularities is a problem.
John, why, are these a problem for you. They are hidden behind
event horizons and they're not hurting you.Let them be.
> Movement of electrons without requiring energy is a problem.
You missed the quantum revolution in the last century, John.
Electrons are not at rest.
> Movement of photons without losing energy is a problem.
John, if a golf ball can move through inter galactic space
without requiring energy (Newton's First Law), why can't
photons. Energy is not required for motion, unless you were
Aristotle.
> Galactic rotation curves is a problem.
Nope, Dark Matter accounts for galactic rotation curves.
> Protons that never degrade is a problem.
Why are protons and electrons lasting forever a problem, John?
> Protons exactly the same size everywhere is a problem.
You don't think protons a bags of quarks, John?
>
> You call photons mechanical?
Mechanical?
>
> john
Answer my questions, John, as to why you have problems with each
of the above. I hope you don't go to your grave, fight what you
don't understand.
John Curtis
>
Sam, DM is a problem.
>
or ptolemaic rotation curves.
Since planets keep pace with the Sun (a star), the galactic rotation
of the planets is also flat, which negates the need for dark matter.
John Curtis
N:dlzc D:aol T:com (dlzc)
"john" <veg...@accesscomm.ca> wrote in message
news:a7f4c30a-790f-4ec6...@d34g2000vbm.googlegroups.com...
...
> Sam, DM is a problem.
DM is a label hung on an observation that indicates there is
non-visible matter, or our current best theory of gravitation is
"scale" dependent. It is not a "problem", it is an opportunity
for future employment.
> Singularities is a problem.
Singularities occur all the time in mathematics. Look at the
process of differentiation. If you refer to "black holes", so
what? A better set of coordinates fixes the singluarity at the
horizon, and even "Bose-Einstein condensates" are singular...
> Movement of electrons without requiring energy
> is a problem.
They do need energy, they need to be balanced with a similar
movement of protons (in a nucelus, say), or they need to be
counterbalanced by electrons moving oppositely. Perhaps you
refer to electrons in a nucleus?
> Movement of photons without losing energy is a problem.
They don't lose energy in a laboratory. They are not waves in
water. We've got plenty of them coming from 12.7 or so billion
years ago. And no current theory (or even Maxwell) expects them
to lose energy "in flight".
> Galactic rotation curves is a problem.
See "future employment" above.
> Protons that never degrade is a problem.
*Not* a problem. No quantum particles "degrade". The second law
applies to *systems* of particles.
> Protons exactly the same size everywhere is a problem.
No. Physics is the same everywhere, so it is an opportunity to
evaluate other things of import.
> You call photons mechanical?
Photons are quantum particles. A "knock in the head" passed
between charges.
What are you trying to say, that Science is not Religion, that we
don't have a Playbook all written out? You are right. Ain't it
great!
David A. Smith