Dark Matter And Its Implications

Definition

Dark matter is non-luminous matter, which can not directly observe, from any form of electromagnetic radiation (light), but whose existence is suggested because of the effects of gravity on the rotation of galaxies and the presence of galaxy clusters.
The density of the universe
The universe as we understand it now with the "Big Bang" when it began a period of very rapid expansion. Astronomers and cosmologists alike have tried to find out whether the universe will continue to expand forever or recollapse in a "big crunch".
It all depends on the ratio between the actual density of the universe to its critical density. Cosmologists call this relationship with the Greek letter Omega. If Omega is larger than a focus will then cause the universe to recollapse if less than one it will expand forever, and if it is equal to one to extend deccelrating rate perpetually.
The critical density of the universe was drawn up more than 5 atoms per cubic metre, which is very little considering that much closer to a perfect vacuum as experimenters on earth will ever hope to achieve.

The actual density of the universe is not known, but if you only the visible material that you stayed with a density of 0.2 atoms per cubic metre. Many cosmologists believe that it is much more matter in the universe can be seen, than by our telecopes, and they have observations and theoretical proof for their beliefs, as I describe in the next few paragraphs.
Rotation of galaxies
Galaxies in the vicinity of the Milky Way appear to be rotating faster than might be expected on the basis of the amount of visible matter, seems to be in these galaxies. Based on their rates of rotation, many astronomers believe that up to 90 percent of matter in a typical galaxy is invisible.

Galaxy clusters
In the universe are stars in galaxies and the galaxies themselves are in clusters. Some astronomers argue that if some reasonable assumptions acceptable - and that the cluster galaxies are linked by gravity, and that the cluster formed billions of years - then it follows that more than 90 percent of the Matter in a particular cluster is made up of dark matter. Otherwise, the proponents argue that interpretation, cluster would not be enough mass to hold it together, and the galaxies would have apart from now.

What is dark matter?
Astronomers and cosmologists know that dark matter exists but do not know what it is, or how much it actually is.
There are many candidates for dark matter, including undetected brown dwarf stars, White Dwarf stars, black holes, or with a mass of neutrinos (Neutrino basic nuclear particles, the electrically neutral and the much smaller mass, if any, as an electron), or even exotic subatomic particles, such as weaklings were (weak Interacting Massive Particles) or macho (Massive Compact Halo Objects). Physicists are currently searching for such particles in underground laboratories (to avoid interference), and learn how to detect them.
This will then recollapse the universe?
Despite the fact that up to 90 percent of the mass of the universe may still be out of the dark matter that cosmologists do not think it would be enough to have the force of gravity halt the expansion and cause a recollapse. This thinking is partly due to observation of supernovae in 1997, suggesting that the expansion is still not speeding up and slowing down at all.
A longer duration universe will not do much, but for us as (it is presumed not known) in the very distant (as distant years 1030 - 1000000000000000000000000000000 years!) If the protons decay, all the stars run out of fuel and are engulfed by Black holes, which in turn radiate all their mass (as in the article on black holes), so that the universe is a large, cold, sterile and lifeless.