Soon after the Big Bang, galaxies started to form as stars were born and were gravitationally attracted to one another in the web of gas formed by the small fluctuations in the density of matter in the young universe. These stars started to form proto-galaxies.

As these galaxies slowly evolved, the first genteration of stars began to die in supernova explosions in the galaxies creating black holes. Through time, these black holes collided and fed on new matter falling into them. This is about the point we reach the stage of evolution of the Quasar galaxy. A quasar galaxy may be the point in a young galaxy's life where the matter falling into the central massive black hole is being ejected by the magnetic fields and momentum created by the gas. We see this as a bright center of a distant galaxy.

As the gas flowing into the center of the galaxy slows down, so does the outflow of matter from the black hole's accretion disk. As this happens, the energy of the material being ejected is decreased and begins to give off signitures in the radio ragime. We see this as a radio loud galaxy. This has been seen in seemigly older galaxies which means it either is a reoccuring process, or a process in a later evolutionary step.

As the galaxies collide, their graviation causes matter to be strewn out over hundreds of thousands of light years. As they gravity begins to pull this material back in, it begins to form larger galaxies. These galaxies may be the spiral galaxies we see in space. How exactly they are formed is unknown but one possibility is the galaxy is disturbed by galactic interactions that cause arms of materials to be pulled from the galaxy then re-incorporated into them. As the galaxies collide and gather other galaxies, they become larger and larger in size.

The final stage of galactic evolution may be the formation of giant elliptical galaxies. These galaxies may have been so disturbed and mixed up they become a large "ball" of stars. It is disputed whether or not elliptical galaxies are the final stage. Though, it does seem to fit.

Galaxies go through galactic collisions throughout their lives. Some grow bigger and some are destroyed. The force behind the collisions is due to gravity. Even galaxies 2.5 million light years apart, such as the Andromeda galaxy amd our own, still have so much gravity that eventually our Milky Way will collide with Andromeda.

Look at the pictures above and you'll see large streams of stars and gas between and around galaxies that were strewn out by the interactions. Some images show only one galaxy hinting that the streamers may be the remnants of a small galaxy ripped apart by the larger.

These interactions can shape and distort galaxies in many ways creating large, long spiral arms, extended spiral arms (in thickness), and seemingly even rings. We're discovering new galactic remnants and interactions every year and these are helping (also with help from computer simulations as seen in the movies above) to further our knowledge of how galaxies form into the shapes we see.

What is Dark Matter and how does it affect galaxies? We're not entirely sure. There are a few forms of dark matter and the most sound version is Warm Dark Matter. It is theorized that it accounts for 20-25% the energy/mass distribution of the universe. It hangs out in the halos of galaxies and only interacts gravitationally. Sounds strange? Unless the calcuations of the speed of star around a galaxy can be solved in another matter (which there are some observations and theories that support this) there is no other explanation for the missing mass inside galaxies.

The pictures above show the distribution of gas, normal matter, and dark matter around a couple galaxy clusters. These have helped astronomers show that there must be something holding the gas and the normal matter apart in the Bullet Cluster (the right image).

Dark matter may be a required mass to help show the formation of galaxies and their distribution throughout the universe. Some scientists have shown mathematically that there needs to be more mass than we see in order for the universe to exist how it does.

So does dark matter exist? Only time will tell.

What else could we call a giant glowing cloud of stars across the sky other than the Milky Way? Our home among the universe containing about 100 billion stars and being approximately 150,000 light years wide. We reside in whats called the Virgo Super Cluster. A giant cluster of 100's of galaxies and smaller galaxy clusters.

The picture above shows our galaxy in multiple wavelengths. Mapping these out gives us the distribution of our galaxy and tells us where our solar system is, where we're goin, and what else is out there. Looking at some of these images (very deeply, not what you'll see here) can give us hints about how our galaxy is structured. Astronomers have discovered that our galaxy is a barred spiral galaxy. We are part of the Orion Spur between the Saggitarius and Perseus arms.