DARK MATTER

Dark matter was proposed by  Fritz Zwiky in 1933 based in the influence of a not vissible mass that affected the velocity of the oribits of th galaxys. Another activities where this influence can be noticed is in the temperature of hot gas in galaxys and in the rotation of them. It is call dark because we cant see it like the stars or planets.

The theoretical model of the composition of the Universe propose that it is composed in the next way: 68% dark energy, ~27% dark matter, ~5% normal matter. 

''Dark matter is one of the great scientific mysteries of the time, but once astronomers accepted its existence, the answers to many other cosmic nmysteries fell into place.''

This unknown material may be, it seems to explain why the disk of our milky way galaxy has such a pronunced warp at its outer rim. Orbiting satellite galaxies naturally tend to distort the galaxy, but their gravitational effect would be to weak without the amplification that dark matter provides.
Another question dark matter answers is why the Milky Way appears to have fewer such satellite galaxies that models predict it should. It turns out that the satellites are probably out there, composed almos enterly of dark matter, making them hard to detect.


October 2011, ScientificAmerican