Galaxies

There are about 200 Billion galaxies in the known universe, with most of those galaxies containing billions of stars. Which is why Carl Sagan loved to say ... "billions and billions and billions of stars."

The Milky Way Galaxy in which we live is about 12 Billion years old. Until less than a century ago it was thought to comprise the whole universe. No other galaxies were known or imagined. In 1924 Edwin Hubble (the man of Red Shift fame who proved the expanding universe and changed cosmology forever) discovered distant galaxies.

But the Milky Way, which spans about 100,000 Light Year,s is a tiny speck when compared to IC-1011, the largest known galaxy, which spans 6 Million Light Years. Our near neighbor, the Andromeda Galaxy is 200,000 LY across.

The Hubble Telescope has seen galaxies which formed about 1 Billion years after the Bang Bang -- some of the earliest and most primitive of galaxies. Stars began forming about 200 Million years after that cataclysmic genesis. These earliest galaxies are lumpy, chaotic, disorganized clusters of stars. Over time, due to the effect of gravity (centered in the super-massive black holes found in most galaxies) galaxies become well-organized, mostly as spirals. The black hole at the center of the Milky Way is thought to be about 1 Million miles across.

But there is a problem. Black holes do not have enough gravitational power to hold galaxies together, or to hold clusters of galaxies together, yet these structures exist. It is now believed that "dark matter" (whose nature is unknown to us) is the thing that holds the universe in order, was probably responsible for the original formation of galaxies, and pervades the universe. There is probably about six times more dark matter than normal matter. This figure is based on the mathematical requirements for the existence of the universe as we observe it. Although its nature is unknown, its presence can be indirectly observed by its gravitational effects on light. A process known as gravitational lensing, in which beams of light are deflected as they pass through deep space, has been observed and measured.

Recently, the universe has been (is being) mapped in 3-D. And what has been discovered is that galaxies, clusters of galaxies, and super-clusters are all found to exist along "filaments" that, in the larger scale, have a sponge-like structure. The universe is weblike, a net made of filaments of galaxies. Gravity, produced by black holes and dark matter, is what determines the form and destiny of the universe.