Our Galaxy is one of one hundred billion

Galaxy is a massive system composed of stars, gas and dust (interstellar matter) and dark matter that is held together by gravity. Still not enough is known about dark matter, but it seems that accounts for 90% of the mass of most Galaxies. It is assumed that in the visible Universe is about 100 billion Galaxies.

They can be a spiral, elliptical and irregular. A common form is the elliptical with a slender elliptical profile, a spiral is in the form of discs with curved arms and there are irregular of unusual shapes and they typically result from the termination caused by the gravitational attraction of neighboring Galaxies. Such interaction can eventually growing into a merge, encourage episodes significantly increased Star formation and produce what is called a starburst Galaxy. Small that don’t have the associated structures are also called irregular.

Galaxy has a range in size from dwarfs with thousands of Stars to giant with 100 trillion Stars, all of them moving in orbits around the center of mass, which contain Black Hole. It is believed that they might be the main cause of active cores found in the centers. Observations indicate that in most of the centers could be a supermassive Black Hole. Galaxies can also contain multiple star systems, star clusters and various interstellar clouds.

Milky Way Galaxy contains 200 billion Stars

The Milky Way is a spiral Galaxy and contains about 200 billion Stars and it’s diameter is around 100.000 light years (30.674 parsecs). The diameters of most of the Galaxy range between 1000 and 100.000 parsecs and usually are mutually separated by millions of parsecs or megaparsecs. Intergalactic Space is filled with a diluted gas with a density less than one atom per square meter. The vast majority are organized in hierarchical societies, which are called clusters, which in turn may associate in super clusters. These larger structures are generally distributed in surfaces and thread that stretch vast cosmic voids.