Scientists now seem to be coming to the conclusion that there is something missing in our understanding of the universe which would account for the effects of gravity on star systems. They have called this "dark matter" which some estimate accounts for three quarters of the mass of the universe. It is not made up of atoms and molecules but of unknown energy which emits no light.

Could this be the real universe? Perhaps UFOs and ghostly visitations are attempts by entities on the dark matter side to reach us?
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Almost...

For Cold Dark Matter models, or Dark Energy theory, both have serious proponents, and have for about 15 years (at least with dark energy).

As for CDM around star systems, it would be safer to describe it in terms of being around galactic clusters. When you take the study down to the level of individual galaxies, there are exceptions to every rule.

As for estimates, it would be more like 15%.
Here's the rub. There is regular, or baryonic, and non-baryonic matter.

After studies (in 2001) on the coldest background energy- microwaves- dark matter and dark energy gained prominent theoretical roles. They were included into Big Bang theory.

Dark energy was thought to be expansive across the gaps between galactic clusters.
There are believers, and non-believers, with strong arguments. But no matter which,
they both believe in some form of 'inflating' energy.

Dark matter is thought to congregate around any sizable galaxy. But, studies are mixed.
X-ray halos are visible around galactic clusters, and it is assumed they result from gas trapped by dark matter (through gravity). When individual galaxies are examined, it is unusual to see large halos, so the theory is that local conditions can vary (collisions, etc).


As for percentages, some sort of inflating energy takes some large portion.
For arguments sake-

75% inflation-related energy.

15% might be the amouint suggested for weakly interacting, cold dark matter. That helps to account for galactic formation and cohesion, and galactic x-ray halos.

6% might be the amount of intergalactic hydrogen and helium. This has been fixed by optical and UV astronomical spectra, using quasars.

3% might be the amount of matter in galaxies.


There is one last thing. Dark matter may be disappearing. It is speculated that very high energy cosmic rays result from collisions or decay of exotic CDM. Some believe that CDM
breakdown results on quark-pairs, which then fragment, and release a diffuse background of 1-100 GeV gamma rays related to this annihilation.

If so, dark matter might have its own particle mass/energy around 50-100 GeV.
You can compare that to a hydrogen nuclei at 1 GeV.


Cold Dark Matter is not exactly the term to use for other dimensional matter/universe.
CDM is theorized to be related to neutralinos (in our universe, and up to 5000 GeV).
However, in theorizing about dimensions beyond our own, one could speculate about other worlds. That involves numerous speculations.


Images-

Illustrative example of distribution of dark matter (which tends toward density areas).

And, x-ray halo around a galaxy cluster. That halo, rather than draining away, is held in place by larger forces, according to CDM theory.

IF SO HELP!!!!! HELP!!!!!! HELP!!!!!! HELP!!!!!

One last example-

Elliptical galaxies may arise from collisions of other galaxies. It is difficult to image an
x-ray halo around them. When elliptical galaxies have initial collisions, they appear to sometimes have the dark matter stripped away by other intergalactic concentrations.

So, exotic cold dark matter is not identified, and is not predictable in a straightforward way, yet.

Image-

This is an unusual example of an individual galaxy, with the x-ray halo super-imposed over the optical image.

ok

Forgive my innocence, but how can this be labeled as matter if it is a form of energy (does not have mass)?

In physics, something mysterious is called "dark".
Lots of money flows for research.

In biology, they just call it "junk DNA", for example.
Not very exciting.

As for 'Dark Energy"-

Some studies on distant supernovae seem to indicate a dividing point on their brightness. Their light reaching us, shows a spectrum of increasing redshift.

So those at 10 billion lightyears, whose multiple images have been recorded from the beginning of supernova to the last image, indicate a spectrum with more peaks around longer wavelengths.

Images of supernova explosions, beginning around 7 billion lightyears away, suddenly
start to have less redshifting spectra, and more blueshifted spectra and light curves.
That light coming towards us got a 'kick', and it shows progressive 'kicking' into the current era.

Some interpret that as a slowing of the expansion curve, followed by a renewed acceleration curve. The term dark energy is used to describe a kind of 'energy to the vacuum', enlarging the depths of space. They reason it is tiny, but incremental and adds up as time goes on. Eventually, they reason, dark matter halos will give up their power to the dark energy tugging at them.


Enter the opposing theories!

Some have argued the tired light model, to explain the tricks of light in a large and dusty universe. I think they have been laid to rest.

Then, there are those who think the universe is like a sheet, where ripples of the original
Big Bang 'inflation' energy shows up from time to time. They stand against staunch dark energy proponents. Whichever side wins, will do so because of better earth and space-based telescopes. There are always plenty of new ones on the horizon.


As for 'Dark Matter'-

The universe had simple energy and matter that was created 1 second after the Big Bang. It filled the vacuum almost instantly, because the vacuum preceeded it.
The whole 'soup' cooled, somewhat. Matter is thought to have condensed and clumped
around an attractor, whose gravity was more than their own. That attractor is a particle,
called Weakly Interacting Dark Matter. It has not yet been thwarted by opposing theory.

Dark Matter does have a cousin- 'normal dark matter'. That is the intergalactic hydrogen and helium, which is largley ionized, and thus- 'invisible' iin the optical spectrum.
Normal dark matter constitutes ~70 % of all normal matter. The heavens are full, in a manner of speaking.

Intergalactic H and He has areas of different density.
Between <1 and 100 hydrogen atoms per cubic meter.

Intergalactic CDM also appears to vary. But, it is theorized to be similar in distribution.
The most promising candidates may be neutralinos. If they are inferred from the new generation of powerful particle accelerators, such as the LHC, then we may discover what Cold Dark Matter really is, or is not!

There are other studies regarding gamma rays that might also tell us about Dark Matter.



Images-

The first one is one way of thinking about the early matter, condensing down around
sections of hydrogen gas, which is condensed around cold dark matter clumps, or halos.

This illustrates the CDM halos attracting large amounts of primordial gas.

Large clouds form, become unstable and undergo runaway collapse.

They form nebulae, then stars, which get ejected downstream, hopefully with planets in tow...

The Cold Dark Matter is involved, through gravity interactions, but not much else.
It does not produce electromagnetic radiation. But, it has mass. The measures I gave above, 50-100 GeV, are ultimately convertable as mass-energy equivalents.