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Grand Universe By Antifon



Evolution


Astronomers study the evolution of galaxies by looking back in time. When viewing an object in space that is 200,000 light years away, astronomers are viewing what that object looked like 200,000 years ago.

The Big Bang caused all of the universe to be uniform. However, there were slight fluctuations in density that caused regions, over time, through gravitational forces, to clump together and form the primordial galaxies. The first stars, within these galaxies, were formed by clumps of hydrogen gas withing the proto-galaxies. The galaxies formed in all shapes and sizes – the smallest ones named tiny dwarf galaxies and the largest ones forming spiral shapes such as the Milky Way Galaxy. Attracted by gravity, these galaxies evolved into large galactic structures known as groups.

The larger the galaxy, the stronger gravitational pull it has on surrounding space bodies. The larger galaxies rip apart smaller galaxies and make them become part of the large galaxy. The Milky Way has taken a few dwarf galaxies and made them part of its galaxy as streams of stars. As galaxies merge they become disc-like and loose their once spiral shape. In a few billion years, this is what will happen with the Milky Way Galaxy and the Andromeda Galaxy. This phenomena of the evolution of galaxies has been occurring for billions of years and will continue to do so.


Types of Galaxies


There are four types of galaxies; Spiral Galaxies, Barred Spiral Galaxies, Elliptical Galaxies, and Irregular Galaxies

Spiral Galaxy-
external image 126032main_spitzer.jpg
This is the most common type of galaxy with approximately 77% of the galaxies in the universe being this type. Basically a spiral galaxy looks like a spiral with arms that spread out from the center of the galaxy, which is commonly known as the bulge or galactic center. There are two types of spiral galaxies. The first is a “face-on spiral galaxy” which basically means you can see the spiral distinctly. The second is an “edge-on spiral galaxy, which is when you see the galaxy on its side. The difference between these two types of spiral galaxies is the direction at which you are looking at them which makes it appear as either face-on or edge-on. The only real difference between all of the spiral galaxies is the fact that some have loosely bound arms and others have tightly bound arms. The arms of the galaxies consist primarily of lots of gas and dust and this is typically where new stars in the galaxy are being formed. The bulge in the center of the spiral galaxy is the place where old stars that were formed primarily when the galaxy itself was formed.



Barred Spiral Galaxy-
The Barred Spiral Galaxy NGC 1300
The Barred Spiral Galaxy NGC 1300

This is basically the same type of galaxy as
a typical spiral galaxy with the only difference
being the fact that they have a bar bright of stars
that run from the center of the galaxy across the
middle of the entire galaxy itself.









ESO 325-G004
ESO 325-G004

Elliptical Galaxy-
These galaxies make up about 10% of the galaxies in our universe. They can either be circular, long, narrow, or cigar-shaped. Typically astronomers use the letter E to show that a galaxy is an elliptical galaxy. They also use the numbers 0-7 to show what the galaxies look like. An E0 galaxy is typically very circular in shape and an E7 galaxy would be very long and thin. There is a large range of sizes for elliptical galaxies. They can range from a million light years in diameter to less than 1/10 the size of the Milky Way. Elliptical Galaxies have very little gas and dust and therefore have little to no star formation. The stars that are in the galaxies are typically extremely old and red and are in the stages of dying off.



Irregular Galaxy-
Irregular Galaxy NGC 55
Irregular Galaxy NGC 55

Only about 3% of galaxies are considered irregular because they cannot be defined as either elliptical or spiral. These galaxies have no specific form, therefore it is very difficult to classify them. There are two different types of Irregular galaxies; Type I Irregular Galaxies and Type II Irregular Galaxies. Type I Irregular Galaxies are most closely related to spiral galaxies if you had to choose a galaxy to relate them to. They have discs and bulges like spiral galaxies, yet they do not have the spiral structure. Also instead of the bulges being in the center of the galaxy, they are typically towards the edges of the galaxy. Type I Irregular Galaxies lack heavy elements, yet they are rich in clouds of hydrogen and when they are heated by near by stars they begin to glow. Type II Irregular Galaxies are usually formed when there is a gravitational reaction with a nearby galaxy. Therefore astronomers typically refer to Type II Irregular Galaxies as “troubled galaxies” because they are most likely to be the galaxies that are part of collisions between galaxies.







Galaxies:



Milky Way Galaxy
Andromeda Galaxy
1 Zwicky 18 (Youngest)
Canis Major Dwarf Galaxy (Closest to Milky Way)
Dwarf Galaxy Leo I
Seyfert Galaxy
M82 Galaxy
M87 Galaxy
M102 Galaxy
NGC 2770 Galaxy
NGC 3314 Galaxy
ESO 137-001 Galaxy
Comet Galaxy
Bode's Galaxy
Cartwheel Galaxy
Cigar Galaxy
Hoags's Galaxy
Large Magellanic Cloud Galaxy
Small Magellanic Cloud Galaxy
Mayall's Object Galaxy
Pinwheel Galaxy
Sombrero Galaxy
Sunflower Galaxy
Tadpole Galaxy
Whirlpool Galaxy
Omega Centauri Galaxy
Trianglulum Galaxy
Centauras A Galaxy
Sculptor Galaxy
Messier 83 Galaxy


All of these are part of what make up our universe:






Resources


Bannister, Nigel. "Irregular Galaxies." (2001): n. page. Web. 30 Nov. 2011. <http://www.le.ac.uk/ph/faulkes/web/galaxies/r_ga_irregular.html>.

Cane, Fraser. "Galaxy Evolution." Universe Today. (2009): n. page. Web. 30 Nov. 2011. <http://www.universetoday.com/30713/galaxy-evolution/>.

"Barred Spiral Galaxy." Science Daily. n. page. Web. 30 Nov. 2011. <http://www.sciencedaily.com/articles/b/barred_spiral_galaxy.htm>.

"Elliptical Galaxies." Sloan Digital Sky Survey/ Skyserver . n. page. Web. 30 Nov. 2011. <http://cas.sdss.org/dr5/en/proj/basic/galaxies/ellipticals.asp>.

"List of Galaxies." Enotes. n. page. Print. <http://www.enotes.com/topic/List_of_galaxies>.

"Spiral Galaxies." Sloan Digital Sky Survey/ Skyserver . n. page. Web. 30 Nov. 2011. <http://cas.sdss.org/dr5/en/proj/basic/galaxies/spirals.asp>.