What is dark matter?

Question

where does it come from?

Answer 1

Sasha thats not dark matter thats somthing that our primitive human camaras cant detect. Remember a coin has 3 possibilites.

Answer 2

Dark matter has been theoretically posited as the main 'matter' gravitational 'element' within galaxies. If dark matter emitted any form of EM radiation, or interacted with it, we would be able to detect its presence due to its dominant presence. However, dark matter may not be an exotic form of matter at all!

Some theorists have speculated that dark matter could be neutrinos. Neutrinos have a very small nuclear weak force cross-section (probability of interaction) and it would take a light-year of lead to block half of the neutrinos produced by the sun. Thus, neutrinos become possible candidates for dark matter due to their low interaction rate with matter. Furthermore, neutrinos travel at either, the speed of light or close to it. In the later speed case, they may have a very small mass of less than 2.2 electron-volts (ev for short. To convert to a mass - multiply by the charge on an electron (e) and divide by c^2 (from E = mc^2)). Hence, with this tiny mass, neutrinos may interact gravitationally with the universe. Evidence from solar neutrino experiments suggests that neutrinos exhibit flavour oscillations during their passage. The flavour oscillations result in an electron neutrino transforming into the muon and then the tau neutrino and then back again. The muon neutrino has a mass of less than 170 kev and the tau neutrino has a mass of less than 15.5 Mev. Thus, flavour oscillations could result in neutrinos having a greater gravitational influence. There is, however, one drawback to this theory - neutrinos move at close to the speed of light and so localised gravitational condensation into proto-galaxies is difficult to account for!

Answer 3

Dark matter was created during  the big bang. Its a cloud of mysterious matter which astronomers haven' yet understood fully. Dark matter contrubits to the gravitational field in space..

Answer 4

unseen light blocker. apparantly weighing couple of hundred tonnes per teaspoon. in space, big black spots in the sky.

Answer 5

we dont know where it comes from yet =P

Answer 6

In physics and cosmology, dark matter is matter that does not interact with the electromagnetic force, but whose presence can be inferred from gravitational effects on visible matter. The observed phenomena which imply the presence of dark matter include the rotational speeds of galaxies, 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

Answer 7

Dark matter is simply mass which we cannot detect by any means other than gravitational effects.

This is most prosaically because it doesn't emit any light or it doesn't reflect or scatter light (more generally, read light as "electromagnetic radiation" to encompass non-visible wavelengths too).

Answer 8

dark matter is a hypothetical form of matter that does not emit or reflect electromagnetic radiation..the gravitational lensing, bending of light etc. are some observable gravitational effects from it..we do not know where it comes from but accounts the majority-over 90%- of the mass in our universe..