|What is a galaxy?|
|"Floating" around the universe are billions of giant islands of billions of stars. Each galaxy contains upwards of 100's of billions of stars, planets, solar systems, nebulae, black holes, etc. Each galaxy we've seen has been unique in its form, and there are many forms to galaxies.|
|casa.colorado.edu||NRAO/AUI and J. M. Uson||R Jay GaBany-Cosmotography.com|
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.
|With so many galaxy types, it has been a struggle for astronomers to classify them. Since the first days of the Hubble Classification, astronomers looked at many aspects of the galaxies to help determine the type. They look at the spirals, bars, elliptical shapes, irregular shapes, dust lanes and overall distribution to help figure out how to classify them. Even with all these aspects of galaxies, we're still trying to make it more precise. Here is one of the latest by the NASA Spitzer team using ifrared wavelengths to classify galaxies.|
|R Jay GaBany-Cosmotography.com||R Jay GaBany-Cosmotography.com||R Jay GaBany-Cosmotography.com||R Jay GaBany-Cosmotography.com||R Jay GaBany-Cosmotography.com|
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.
|How Many Galaxies?|
|Welcome to the Hubble Ultra Deep Field. An image 10x smaller than the full moon but containing an estimated 10,000 galaxies. The image shows galaxies approximately 13 billion light years away. That's only 300-400 million years after the big bang. Almost every spot of light in this image is a galaxy. This one image shows you the vastness of the universe and how many galaxies could potentially be in it, billions in fact. Each galaxy may contain 100's of billions of stars and may contain millions of planets with life of them. With so many places to hide, it's hard to claim life is only here on Earth.|
|Our Galaxy: The Milky Way|
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.