Dark matter, why?

Hi,

I have couple of puzzles I don't understand. Can anyone help out?

(1)
Why there must be dark matter in the galaxies?

From what I can understand, it has something to do with the tangential
velocity of galaxies and the distance to its center.

Qoute from my text book:
"
v = sqrt(GM/r)
According to this model, we exspect stars beyond the Sun to have
tangential velocities that decrease with increasing radius like r^(-1/2).
"

(2)
Why do we expect that?


(3)
And it should also have something to do with the Kepler approch
not being valid for galaxies. Is that because galaxies are spirals?

Regards,
Martin

During a perfect moment of peace at Thu, 14 Aug 2003 12:21:31 +0200,
Martin Jeppesen interrupted with:

(1) Why there must be dark matter in the galaxies?
From what I can understand, it has something to do with the tangential
velocity of galaxies and the distance to its center.

Qoute from my text book:
" v = sqrt(GM/r). According to this model, we exspect stars beyond the Sun to have
tangential velocities that decrease with increasing radius like r^(-1/2)."
(2) Why do we expect that?

Because Galaxies are non-rigid bodies. If it was a rigid body the
radial velocity would be a constant across the disk, so the linear
velocity increases with radius. Instead we do expect Keplerian style
motion. This is not observed, the motion of the spiral appears to be
that of a rigid body. Note that the core region does have keplerian
style motion.

This, at present, is only explained if the Galaxy is embedded in a
larger mass. But that mass should radiate (be visible) at some
wavelength. It is not so the mass is called 'dark'.

(3) And it should also have something to do with the Kepler approch
not being valid for galaxies. Is that because galaxies are spirals?

Not at all. Even Elliptical galaxies show evidence for dark matter.
Ellipticals behave like gas under pressure, stellar motion is random
like atoms in a gas. Stars are observed with velocities far higher
than the escape velocity of the Elliptical. This is explained by the
galaxy being embedded in a larger mass.

The 'problem' is also seen at larger scales. The velocities of
individual galaxies in clusters are higher than the escape velocities
of the cluster. The so called mass/light ratio is also wrong.
Basically, the evidence for dark matter is seen everywhere or our
knowledge of gravity is sorely wrong, which has passed every other
test thrown at it.

Nature can create dark matter faster than fusion can take place. Nature
uses fast acting stars(great density) and in just say 5 million years
dark matter is created by the explosion(supernova) Our sun creates dark
matter(up to iron) but that is a long slow fusion process. 93 % of the
universe is dark matter for these reasons(after the BB) and during the
BB. During the BB it was BH that came out of it. Since nature
loves to balance, all the black matter that came out of the of the BB
was proportional to the matter that would give light to the universe.
Bert PS a little choppy typing(yes) but I think I made a point not to
hard to figure out

"G=EMC^2 Glazier" wrote in message
...
Nature can create dark matter faster than fusion can take place. Nature
uses fast acting stars(great density) and in just say 5 million years
dark matter is created by the explosion(supernova) Our sun creates dark
matter(up to iron) but

Sorry, that's a misunderstanding. Dark matter isn't just normal matter that
doesn't radiate. Dark matter is generally theorized to be a different type
of matter entirely that doesn't interact with normal matter except for
having mass and therefore a graviational field (please don't nag me about
using the word "field").

Dark matter theories come in two types last time I looked: WIMPs (Weakly
interacting massive particles) or MACHOs (MAssive compact halo objects). I
am NOT kidding. The point is that because these theoretical objects don't
interact with normal matter (or each other), they form a globular cloud
rather than a disk (the flattening of a cloud of normal matter into a disk
happens because the particles can collide). This cloud of dark matter
provides a large diffuse gravitational field (shaddup) that supposedly
explains the unexpected movement of stars in the galaxy.

Where dark matter comes from, how it was formed, and what it's made of are
left as excercises for the reader, or the god of your choice.

During a perfect moment of peace at Thu, 14 Aug 2003 16:40:51 -0400
(EDT), (G=EMC^2 Glazier) interrupted with:

Nature can create dark matter faster than fusion can take place.

Bert

You say you like to think and look for sameness, get your neurons
around this one.

For starters, Dennis has it right. Dark Matter is not just normal
matter, it is (or seems to be) something we have no knowledge of.
Current estimates put it at around 60% of the mass of the Universe.
Another 30% or so of the Universe is in the form of Dark Energy, that
which causes the hubble flow to accelerate. These are two very
seperate things at present.

Now for some wild speculation which I can not back by experiment let
alone theory.

Whatever Dark Matter is it is created in the Big Bang along with
Baryonic (normal) matter that creates stars. Also, after the Big Bang
occurs the universe inflates tremendously due to an Inflanton field.
This is inflanton is linked to a Higgs field that drives inflation.
Mass is currently thought to be particles interacting with a seperate
scalar Higgs field.

Mass (Dark and Baryonic) creates gravity and gravity in turn is
thought to counteract the Universes expansion. Though it is now
thought there is some extra component counteracting that as well.
Also, when baryonic mass is created it is thought that equal amounts
of matter/antimatter are created that later, through CPT violations,
becomes one form only. (I have yet to see an explanation of why
Baryons created during baryosynthesis on the first 10^-33 or so
seconds favour one form, only leptonic matter at the surface of last
scattering).

So, do you see a common theme here. Higgs fields cause inflation,
another Higgs field is responsible for mass. Mass in turn causes
gravity and gravity is a warping of spacetime created along with
baryonic/non-baryonic matter.

Given Physics holy grail is a super-symmetrical TOE or GUT it seems to
me there is some (as yet unknown) underlying quantum gauge field that
everything - mass (all forms), gravity, inflation - couples to. Large
scale structures then become variations in the energy density of this
field.

As I say, wild speculation without as much as one equation to back me.
This immediately qualifies me as an out and out kook. But I have seen
some recent papers in Ap.J. (I think) speculating Gravity is a field
shared between brane worlds. As ever the theoreticians are way ahead
of the field in speculation.

Dave "SO(5)U(2) rulz" Barlow

Here is an alternative explanation for the non-Keplerian (unitary or
'frisbee-like') rotation of galaxies. It's been posted here before-
http://mb-soft.com/public/galaxy.html

oc

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Hi oc that is a great site. I"m making a print out of it. The part that
I read so far that I find is stars,and our sun that make up each arm are
oscillating across the width of each arm.Hmmmm. Bert PS Thank you

During a perfect moment of peace at Fri, 15 Aug 2003 08:29:19 -0700
(PDT), (Bill Sheppard) interrupted with:

Here is an alternative explanation for the non-Keplerian (unitary or
'frisbee-like') rotation of galaxies. It's been posted here before-
http://mb-soft.com/public/galaxy.html

The author of that page seems blissfully aware of the work of Lin and
Shu who have posited a theory for why Spiral Galaxies are spiral. This
work dates back to the mid-60's to boot ans is called the Lin-Shu
Density Wave Theory.

There have already been many computer simulations run using a not
dissimilar analysis to what the author suggests. I.E. Take a standard
element of galactic arm material, build a galaxy using mutliple
components and then rotate the lot to see how it evolves. The analysis
support Lin-Shu and in no way further explains why galaxies rotate
with non-keplerian motion. Look up stochastic models of spiral
evolution.

Basically, the above is not an alternative explanation of anything. It
is a very poor and very weak attempt at something though.

During a perfect moment of peace at Sat, 16 Aug 2003 08:29:25 +0100,
Dave Barlow interrupted with:

The author of that page seems blissfully aware of the work of Lin and Shu

Really must proof read my posts one day; s/unaware/aware;

During a perfect moment of peace at
Sat, 16 Aug 2003 08:29:25 +0100, Dave
Barlow

interrupted with:

The author of that page seems blissfully
aware of the work of Lin and Shu

Really must proof read my posts on
day; s/unaware/aware;

Actually the author is quite aware of the density (or 'shock')-wave
model, if you care to read the article-
http://mb-soft.com/public/galaxy.html

oc

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