what is dark matter?

Answer 1

In astrophysics, dark matter refers to matter that does not emit or reflect enough electromagnetic radiation (such as light, X-rays and so on) to be detected directly, but whose presence may be inferred from its gravitational effects on visible matter. Among the observed phenomena consistent with the existence of dark matter are the rotational speeds of galaxies and orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter also plays a central role in structure formation and Big Bang nucleosynthesis, and has measurable effects on the anisotropy of the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than is directly observable, indicating that the remainder is dark.

The composition of dark matter is unknown, but may include new elementary particles such as WIMPs and axions, ordinary and heavy neutrinos, dwarf stars and planets collectively called MACHOs, and clouds of nonluminous gas. Current evidence favors models in which the primary component of dark matter is new elementary particles, collectively called nonbaryonic dark matter.

The dark matter component has vastly more mass than the "visible" component of the universe. [1] At present, the density of ordinary baryons and radiation in the universe is estimated to be equivalent to about one hydrogen atom per cubic meter of space. Only about 4% of the total energy density in the universe (as inferred from gravitational effects) can be seen directly. About 22% is thought to be composed of dark matter. The remaining 74% is thought to consist of dark energy, an even stranger component, distributed diffusely in space. [2] Some hard-to-detect baryonic matter (see baryonic dark matter) makes a contribution to dark matter, but constitutes only a small portion. [3] [4] Determining the nature of this missing mass is one of the most important problems in modern cosmology and particle physics. It has been noted that dark matter and dark energy serve mainly as expressions of our ignorance, much as the marking of early maps with terra incognita

Answer 2

Christian's answer is quite good but unless you have a thorough understanding of cosmology it is quite hard to follow.

If you do the maths behind the velocities that galaxies are rotating you will find that a certain amount of mass will be required in order to have enough gravitational attractive force to keep the outlying stars.

The idea behind this is that as you rotate parts of you feel a force that wants to fling you outwards.

Back to the point, if you calculate the mass of a galaxy my counting stars and multiplying etc you will find that there is no where near enough mass to back up the previous calculation.

Dark matter is a physicists excuse to account for this missing mass. It is matter that is not detectable or visible. A bit of a cop-out really, but this is actually a very serious problem.

If you want me to try and explain more, email me at [e-mail]

Cheers

Chris

Answer 3

It's a fudge factor like imaginary numbers in algebra.

When mathemeticians and scientists reach a dead end in their calculations they have to invent some wigged out theory to make everything fit.

Cosmologists can't explain why the universe is expanding so quickly when it contains relativley little amount of matter. Consequently, they had to invent this invisible force that is pushing everything away.

Lo and behold, dark and scary matter was born.

It's an interesting concept but still very much a theory like everything else in science. Science seeks truth but doesn't always find it.

But as a sadly misguided explorer once said, "It is better to seek and not find than to never seek at all".

He was searching for the fountain of youth.

Answer 4

Anything that has mass but doesn't interact with not emit light. Dark matter is the solution to the fact that there appears for be gravity and hence matter than we see in stars.

There are lots of possible candidates but none at the moment see to be able to account for the entire missing mass which is about 90% of the entire universe.

Answer 5

dark matter

Nonluminous matter not directly detectable by astronomers, hypothesized to exist because the mass of the visible matter in the universe cannot account for observed gravitational effects. Long believed to exist in large quantities, it enters into many theories of the origin of the universe and its present large-scale structure and into models of gravitation and other fundamental forces (see fundamental interaction) between particles. Numerous candidates for dark matter have been proposed over the years, but none has yet been confirmed.

Answer 6

As per the latest postulates on our universe what ever matter we see (and hither to believed that universe only consists of all this) namely solar system,stars,nebulae,galaxies, milky way etc constitute only 5% of matter. Rest 95% is dark matter of which not much is known. It does not reflect light. It is a kind of "Galactic Glue" and is believed to be responsible to keep the universe together in spite of galaxies running away from each other (Hubble"s theory). The gravitational force exerted by this dark matter has been recently seen to be responsible for holding stellar matter together.

Answer 7

No one really knows yet. They added up all the mass in the universe and it didn't come to enough to keep the universe together, so they said that there must be something out there that they cannon see. And that's not just visable spectrum, it has to be something that doesn't even give out heat, or x-rays, or radio waves. There is a lot of speculation as to what it could be, and what properties it has.

Answer 8

dark matter is a matter presumed to exist without reflecting any kind of known radiation (slightly stupid, if you ask me)

Answer 9

The atmosphere without any light is called dark and its colour is black.

Answer 10

dark matter doesn't reflect light