Dark Matter in a Galaxy

October 30, 2009

An false-color infrared image of the faint, edge-on galaxy UGC 7321 as seen with the Spitzer Space Telescope IRAC camera. Astronomers modeling the galaxy have concluded that dark matter plays an important role in determining the dynamics of the inner as well as the outer regions of this galaxy. Credit: NASA, and Lynn Matthews/Kenneth Wood

(PhysOrg.com) -- Stars, the most familiar objects in the night sky, make up only a tiny percentage of the total amount of matter in the universe -- about 2%.

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Another approximately 8% of the matter is in objects that have never been directly seen because, for example, they might be too cool to radiate much visible light; scientists estimate this percentage indirectly, from the relative abundances of hydrogen and helium gas and other sensitive monitors of the existence of other kinds of atoms.

The vast majority of matter however, nearly 90% of the total, is in some unknown form. Its presence is inferred from the motions of galaxies: their rotations, their motions as members of clusters of galaxies, and their behaviors in the expanding universe. This dominant and mysterious type of matter has been dubbed "dark matter." We do not know what dark matter is, only that it is unlike the particles that comprise normal atoms. Clues to its nature, however, may be found in where it is located and how it is distributed. Astronomers therefore probe galaxies looking for these elusive hints.

The galaxy UGC 7321 is a spiral galaxy, seen edgewise, with a highly flattened disk of stars lacking the central bulge commonly seen in many spirals. Many studies have modeled dark matter based on the way its gravity influences the rotation of the galaxy's disk at radii far from the center, but recently astronomers have tried examining how dark matter might be influencing the behavior of matter perpendicular to a galaxy's disk. SAO astronomer Lynn Matthews, along with two colleagues, used UGC 7321 to study this perpendicular influence for the first time in a faint, thin galaxy.

The astronomers modeled the stars and gas of the galaxy with a halo of dark matter whose gravity constrains both the radial and the perpendicular shape of the system.

They conclude that a consistent picture emerges with a dark matter halo whose average density is equivalent to about 500 earth-masses per cubic light-year, and whose presence is influential even within the inner spiral regions of the galaxy (a few thousand light-years), in contrast to the case in more luminous, massive galaxies where stars and gas overwhelmingly dominate the dynamics of the inner regions.

The new results imply that dark matter permeates a galaxy, and is not constrained to exist in the cold outer regions of intergalactic space. Although this does not seem to be a surprising conclusion, with matter that is a mystery every bit of information is valuable.

Provided by Harvard-Smithsonian Center for Astrophysics (news : web)

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hessimoto
Oct 30, 2009

Rank: 3 / 5 (2)

I still don't know why I haven't seen anything ruling out frame-dragging, or the Lense-Thirring effect, to account for any of the dark matter "effects". Does the uncertainty of the amount of non-radiating material(dust, brown dwarfs, dead cinders, rogue black holes, etc), along with the Lense-Thirring effect even come close to what we now see as the apparent effect of something we don't know, e.g. dark matter? Just curious.

degojoey
Oct 30, 2009

Rank: 1 / 5 (1)

i fully agree with you! I think they dont account for enough gravity inside a galaxy or even comprehend it on that grand of a scale.

RobertKLR
Oct 30, 2009

Rank: 4.2 / 5 (5)

Isn't dark matter really just a fudge factor used to make the math agree with observation? Some say the math describing gravity is wrong, something is missing.

NeilFarbstein
Oct 30, 2009

Rank: 3 / 5 (4)

I still don't know why I haven't seen anything ruling out frame-dragging, or the Lense-Thirring effect, to account for any of the dark matter "effects". Does the uncertainty of the amount of non-radiating material(dust, brown dwarfs, dead cinders, rogue black holes, etc), along with the Lense-Thirring effect even come close to what we now see as the apparent effect of something we don't know, e.g. dark matter? Just curious.

I contacted the author of the papers on antigravity beams projected via the lens thirring effect affecting the radial velocity of galactic matter as opposed to dark matter theories, Frank Felber; He told me somebody in the audience of a lecture he gave had the same idea in 2006. I thought that I had thought of it first.

Woutertje
Oct 31, 2009

Rank: 2 / 5 (3)

My opinion is that dark matter didn’t exist,
The too high star speed presented by flat galaxy rotation curves, are an effect of the density waves that are responsible for the spiral pattern. Density waves go faster in the exterior regions of a galaxy.
What we now about gravity is how a mass behave in an gravitation field. With density waves we speak about changes of a gravitation field that goes faster around the galaxy then the stars of this galaxy. At 15 kpc is the speed of the density waves +/- 9 times faster as the stars. This makes that the change of the gravitational field cause by the density wave is +/- 9 times higher then what standard theory’s says about the density waves. I didn’t have a mathematical framework for this part of my cosmology. Wouter Vanhoutte

iFujita
Oct 31, 2009

Rank: 1 / 5 (2)

There are three phases of the relation of gravitation and separation.

elliptical galaxy e.g. NGC4881 "Three Dimension" ordinary Newton's equation
GM(

iFujita
Oct 31, 2009

Rank: 1 / 5 (2)

There are three phases of the relation of gravitation and separation.
elliptical galaxy e.g. NGC4881 "Three Dimension" ordinary Newton's equation
GM(smaller than r)m/r^2 = mv^2/r
gravitationally unstable

barred spiral galaxy e.g.NGC1300 "One Dimension" new New1ton's equation
G''M(smaller than r)m = mv^2/r

spiral galaxy e.g. NGC4414 "Two Dimension" new New2ton's equation
G'M(smaller thanr)m/r = mv^2/r
gravitationally stable

There are also phase-shifts among those three phases.

Iori Fujita

http://www.geocit...y01.html

zevkirsh
Oct 31, 2009

Rank: 1 / 5 (1)

dark matter is nonsense. once mankind travels far enough to a reasonably distant galaxy at least a billion light years away, we will discover that most of what we thought was missing is actually too far too see from earth but can be viewed from other distant locations, of course, from those locations, some of what is visible from earth , will then become invisible.

pauldentler
Nov 01, 2009

Rank: 1 / 5 (1)

In the not too distant future a new model for the universe will come into vogue as a hypothesis to account for the effects of 90% of the gravitational forces we see demonstrated throughout the universe. Today we call it "dark matter", "dark matter" will eventually morph into a new model of the universe & carry a name something like "the orbital universe", a model depicting all the galaxies in orbit about a central core similar to the structure of our solar system. This kind of model will account for red & blueshifting of galaxies near & far that the Big Bang model cannot explain, and at the same time account for the source of all that gravity that cannot be explained by the content of the viewable universe.
Remember you read it first coined here:ORBITAL UNIVERSE

Parsec
Nov 01, 2009

Rank: 5 / 5 (3)

Every time I read an article about aspects of dark matter, I see lots of comments that dark matter doesn't exist. Maybe someone here can answer me. Is this opposition to the idea based on a personal philosophy/ideology? Or maybe you believe you understand the science better than anyone else?

I have read extensively on the subject and while I don't pretend to understand all of the science involved, I do understand that there are multiple converging lines of evidence upon which dark matter theories exist. There are also competing gravitation theories which basically modify Einsteins gravity equations at very large scales. The difficulty with the gravity theories is that they don't work in all circumstances.

At any rate, I can positively and without fear of contradiction say that truth is unresponsive to personal wishes. Just because you don't like a theory doesn't mean that its not the truth. And visa versa.

frajo
Nov 01, 2009

Rank: 2.8 / 5 (4)

Every time I read an article about aspects of dark matter, I see lots of comments that dark matter doesn't exist. Maybe someone here can answer me. Is this opposition to the idea based on a personal philosophy/ideology? Or maybe you believe you understand the science better than anyone else?

[1] Unfortunately, most articles about DM forget to mention that the existence of DM is not proven. You don't need to be a professional scientist to see this flaw.
[2] There is no idea how the constituents of DM fit into the standard theory of particle physics. Everytime some experiment or observation is done to pin down a certain elementary particle as constituent of DM, as a result this elementary particle must be excluded from the set of candidate constituents.
[3] There are alternative cosmologies without DM.
[4] There is an "invisible hand" in DM: http://www.physor...210.html
[5] The unphysical idea of a "beginning of time and space" is religious/metaphysical thinking.

vidar_lund
Nov 01, 2009

Rank: not rated yet

I still don't know why I haven't seen anything ruling out frame-dragging, or the Lense-Thirring effect, to account for any of the dark matter "effects".

In most cases framedragging causes minute effects that can only be observed through detailed observations. The 'too fast' spinning of the galaxies is not such a minute effect, it's a very big effect.

pauldentler
Nov 01, 2009

Rank: not rated yet

[3] There are alternative cosmologies without DM.

Do these "alternative cosmologies" delve into the issue of accounting for the missing source of 90% of the gravity in the universe?

vidar_lund
Nov 01, 2009

Rank: not rated yet

Every time I read an article about aspects of dark matter, I see lots of comments that dark matter doesn't exist.

If you look above your comment you see one guy introducing the 'Orbital Universe' and another guy talking about us not being able to see the matter in other places unless we travel to those distant galaxies. Unfortunately this forum is flooded with comments from people who seems to have no education in physics, astronomy or cosmology but yet they know that dark matter doesn't exist (or they know that the sun is actually a neutron star).

I don't find it hard to believe in dark matter at all, the history of science is full of big discoveries and some are yet to be made. The evidence for some huge invisible mass acting upon the galaxies is very strong and this cannot be explained by modifying Einsteins field equations on a large scale. The problem is that dark matter is observed in galaxies that are 'very small' on a cosmological scale.

frajo
Nov 02, 2009

Rank: 1 / 5 (1)

[3] There are alternative cosmologies without DM.

Do these "alternative cosmologies" delve into the issue of accounting for the missing source of 90% of the gravity in the universe?

One alternative theory is the Ekpyrosis of Steinhardt and Turok. It does account for the missing mass in a very elegant way: The observable universe lies in a brane with 3 space dimensions and 6 curled-up dimensions. There is another 9-dimensional brane at a certain distance along a tenth dimension. According to the equations of M theory all familiar particles and forces are confined to our brane. Except gravity. A lump of matter in the other brane generates a gravitational force pulling matter in our brane toward the point directly opposite the lump.

Justavian
Nov 02, 2009

Rank: not rated yet

...A lump of matter in the other brane generates a gravitational force pulling matter in our brane toward the point directly opposite the lump.

Would that indicate that galaxies on our brane can only form where there is a corresponding mass on the other brane? Can you imagine an experiment that might allow us to investigate that idea?

pauldentler
Nov 02, 2009

Rank: not rated yet

...A lump of matter in the other brane generates a gravitational force pulling matter in our brane toward the point directly opposite the lump.

Would that indicate that galaxies on our brane can only form where there is a corresponding mass on the other brane? Can you imagine an experiment that might allow us to investigate that idea?

So, here is food for thought (brane). Gravity appears to be of equal distribution as it permeates all matter & overcomes the other forces of the "brane string theory". Gravity being so equally distributive throughout the observable universe is of significant portent & unexplainable with current cosmological models. We can locate the nuclear forces that operate within the "brane string", but cannot locate the source of 90% of gravity.

AnotherNoName
Nov 03, 2009

Rank: 4 / 5 (1)

[1] Unfortunately, most articles about DM forget to mention that the existence of DM is not proven. You don't need to be a professional scientist to see this flaw.
[2] There is no idea how the constituents of DM fit into the standard theory of particle physics. Everytime some experiment or observation is done to pin down a certain elementary particle as constituent of DM, as a result this elementary particle must be excluded from the set of candidate constituents.
[3] There are alternative cosmologies without DM.
[4] There is an "invisible hand" in DM: http://www.physor...210.html
[5] The unphysical idea of a "beginning of time and space" is religious/metaphysical thinking

The alternative cosmologies must have testable, unique explanatory power. It will be great when we have something more satisfying than "dark x;" we do not yet. And, all cosmologies end up with metaphysical propositions. To deny this is usually to change the meaning of the word "metaphysical."

frajo
Nov 06, 2009

Rank: 1 / 5 (1)

Yes, alternative models must be falsifiable.
No, two different models may not have unique explanatory power. That's what Occam's Razor is for.
Satisfaction lies in the eye of the beholder. The beauty of string based models like the ekpyrotic/cyclic model is very satisfying. It answers many questions the standard model leaves open.
A cosmological model which can describe the universe without implying an initial point for the validity of the laws of physics has IMHO less metaphysical burden to bear.

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Dark Matter in a Galaxy

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