Can someone explain to me the theory behind Dark Matter?

Question

what exactly is it?

Answer 1

dark matter, material that is believed to make up (along with dark energy) more than 90% of the mass of the universe but is not readily visible because it neither emits nor reflects electromagnetic radiation, such as light or radio signals. Its existence would explain gravitational anomalies seen in the motion and distribution of galaxies. Dark matter can be detected only indirectly, e.g., through the bending of light rays from distant stars by its gravity.

Dark matter may consist of dust, planets, intergalactic gas formed of ordinary matter, or of MACHOs [Massive Astrophysical Compact Halo Objects], nonluminous bodies such as burned-out stars, black holes, and brown dwarfs; these are the so-called hot dark matter and would be dispersed uniformly throughout the universe. The discovery in 2001 of a large concentration of white dwarf stars in the halo surrounding the Milky Way indicates that these burned-out stars could represent as much as a third of the dark matter in the universe.

Other theories hold that it is made of elementary particles that played a key role in the formation of the universe, possibly the low-mass neutrino or theoretical particles called axions and WIMPs [Weakly Interacting Massive Particles]; these are the so-called cold dark matter and would be found in clumps throughout the universe. In 1996 a Japanese team at the Univ. of Tokyo led by Yasushi Ikebe reported on dark-matter clumping in the galactic cluster Fornax. Clumps were found in two distinct regions: around a massive galaxy in the center of the cluster and, in larger amounts, around the entire cluster. This suggests that the slower, cold dark matter might form the smaller clumps associated with the galaxy while the faster, hot dark matter might form the larger clumps associated with the galactic cluster.

Computer simulations of the formation of the universe favored the cold dark matter but tended to predict the formation of too many dwarf galaxies when compared to the observed universe. This led to the postulation of warm dark matter, which resolved the simulation problems. Unlike cold dark matter, which has mass but virtually no velocity or temperature, or hot dark matter, which has mass and is highly energetic, warm dark matter has mass and a low temperature corresponding to an extremely low velocity.

http://www.answers.com/main/ntquery?s=dark+matter&x=7&y=14

Answer 2

There is no theory behind it, so it should really be called unknown matter.

Its existence is deduced from observation. If you look at the motion of stars and galaxies, and then try to explain it in terms of the matter they contain and the laws of physics, you find that the motion can only be explained if there is about 10 times more mass than you had actually found.

The missing mass cannot be the stars themselves, or dust, or particles, or interstellar hydrogen, or any of those other things that you have already measured because you can see them. It must be something that does not interact so that it can be seen, but that does have mass and so affects gravity.

We do not know of anything that behaves like this, but our observations tell us that it must be there.

Answer 3

I'm not sure you can say it does exist. It's presence is inferred by viewing other phenomena. There are some people who believe that the standard model is in need of an overhaul which would eliminate the need for Dark Matter. We'll just have to wait it out to see what's really going on.

Answer 4

Actually It is presence was’t just theorized there are real phenomenas to support the theory , even though it is invisible, it’s gravitational effect on visible matter proved it does exist.
Among them ,the orbital velocities of galaxies and the rotational speeds of galaxies
In clusters , gravitational lensing of background objects by galaxy clusters like bullet cluster and the distribution of temperature of hot gas in galaxies and their cluster are all affected by it.
It is difficult to detect it directly becuz it doesn't emit or reflect enough electromagnetic radiation and it’s invisible but it proves it’s existence by affecting visible matters so it does exist.

dear, i realized non of us really answer your question, if you want to know what is behind it you should give time for scientist to figure what exactly is it at the first place.

Answer 5

..........."As we shall discuss in more detail later, there is abundant evidence that the vast majority of matter in the Universe does not show up in our telescopes but we can infer its presence by its gravitational influence. We refer to this as dark matter <../cosmology/darkmatter.html>, and at present we do not know what it is, though there is fairly strong evidence that it is not the ordinary matter of stars, gas, dust, and planets. In our own galaxy, the observed of the stars and gas clouds indicates that the visible matter is surrounded by a halo of this dark matter containing the major portion of the total galaxy mass and extending very far beyond the visible matter. Some indirect means suggest that the dark matter halo may extend as far as 100,000 parsecs from the center of the galaxy."...........

I had this paragraph somewhere between my papers....and I can't remember where I got it from....


but I got something else here as well...Its worth to check it:)

http://csep10.phys.utk.edu/astr162/lect/cosmology/darkmatter.html

Answer 6

That technological understanding has grow to be a fantasy land the position some thing will be dreamed as a lot as help persevering with the elementary flaws and lies that seventy 5% of theoretical technological understanding is equipped upon. Why attempt and habit study in accordance with shown data, once you are able to only make it up as you bypass alongside. Its pathetic that more suitable then 50% of technological understanding is hypothesis! no longer to point how could we likely locate some thing they declare cant be detected and would not artwork jointly with remember or capacity, they defy their own statements!

Answer 7

Here yo go :-)

Dark matter is just what its name implies; it is matter (or mass) in the universe that we cannot see directly using any of our telescopes. Our telescopes see not only visible radiation (constituting the spectrum of colors that our own eyes can detect), but other types of radiation as well.

You can find out more here
http://www.sciam.com/askexpert_question.cfm?articleID=0007AF2A-5F25-1C71-9EB7809EC588F2D7