Abstract:
Modern astronomers have made significant progress in determining what the universe is mostly composed by what substance. By utilizing the Wilkinson Microwave Anisotropy Probe (WMAP), scientists discovered that the universe (for the first a few hundred thousand years) was an expanding gas composed primarily of protons, electrons, photons, neutrinos, and the mysterious dark matter. In the present, scientists are still bombard about dark matter and what it really is. Although, scientists do not know what dark matter is, they are certain of what it is not. Dark matter is not in the form of stars and planets that we see and it is known to make up about 25% of the entire Universe. By using the effect of gravitational lensing, astronomers are able to determine that dark matter is not affected by most of the other baryonic matters. They also found that dark matter is the responsible substance that makes up most of the masses in the universe (found in galaxies, dwarf galaxies, and cluster galaxies). Dark matter is also the primary influence of gravitational pulls. The mysterious and magnificent space that seems almost empty to the naked eye has fascinated mankind for as long as history can remember. The universe seems empty because it is made up of gas which is primarily composed of particles such as protons, electrons, photons, neutrinos, and dark matter. Dark matter is known to make up about 25% of the entire Universe but scientists have yet to understand completely about this mysterious subatomic particle. What is dark matter and where did it come from? What is really the natural function of dark matter? Where and how can dark matter be found? These questions have been the ultimate challenge for astronomers for the past decades. Scientists and Astronomers have always known that dark matter influenced the cosmos in many different ways because it makes up 25% of our entire Universe (Dark E, 2012). Yet, scientist has not found the primary function of dark matter and what it really is. Although dark matter remained mysterious for the longest time, technology has opened new doors and offered conventional ways for astronomers to study dark matter. The Wilkinson Microwave Anisotropy Probe or WMAP revealed what the universe was like when it was only a few hundred thousand years old, long before galaxies and clusters of galaxies were formed. After the Big Bang, the universe was an expanding gas composed primarily of protons, electrons, photons, neutrinos, and dark matter (Refer to Figure 1.0 & 1.1). WMAP and other data, as well as many different lines of evidence suggest that the mass of dark matter in galaxies, clusters of galaxies, and the universe as a whole is about 5 or 6 times greater than the mass of ordinary baryonic matter such as the protons and neutrons. The WMAP results also hint that dark matter likely takes the form on an as-yet-undiscovered subatomic particle known as Weakly Interacting Massive Particle (WIMPs) which represent one hypothesized class of these particles. They neither absorb nor emit light, and don’t interact strongly with other particles. Yet when they encounter each other, they annihilate and make gamma rays (Fermi, 2012). This finding has led astronomers to discover even more of what dark matter can do with relation to other particles such as protons, electrons, neutrinos, and so on.
Scientists have gathered massive amounts of evidence proving that protons, electrons, photons and neutrinos all exist in stars and galaxies. These particles are also known as baryonic matter because they are detectable when they absorb radiation. In the other hand, dark matter behaves very differently because it does not frequently interact nor does it interact well with other particles such as proton, electrons and so on. In fact, in 2007 results from the NASA’s Hubble Space Telescope confirmed that dark matter and galaxies parted ways in gigantic merging galaxy clusters, this event was seen in galaxy clusters like Abell 520 which is located 2.4 billion light years away (Dark M, 2012). When this cluster was detected around 80 years ago, scientists believed that dark matter was some kind of gravitational glue that holds other substances together, it was also believed to be the primary influence responsible for the shapes of galaxies and galaxy clusters. This theory came to be when scientists discovered dark matter by accident from observing its gravitational influence effect on its surroundings. This method is referred as gravitational lensing which was succeeded with the help of the Canada-France-Hawaii and Subaru telescopes on top of Mauna Kea when it tried to measure the bended light from the more distant background galaxies but were unable to due to the gravitational influence from the dark matter. From the studies of the galaxy clusters like Abell 520, it proved that the function of dark matter is not as simple as other substances. The observation showed that the system’s core was indeed rich in dark matter but it lacks the luminous galaxies which are normally found in the same location as dark matter. Another recent discovery known as Abell 2744 (Pandora’s Clusters) provided deeper understanding on these galaxy clusters and their functions as well as how they behave, grow and affect their surroundings. It also provides new insights on the properties of dark matter. By utilizing the phenomenon effect from gravitational lensing, astronomers are able to pinpoint the location of dark matter and its function. From the images taken from multiple type/sets of telescopes (refer to figure 2.0), astronomers were able to deduce that the Abell 2744 clusters are actually the result from at least four different galaxy clusters collisions (Abell, 2011). Astronomers were able to confirm and conclude this hypothesis by noticing the variety of compositions and the differences in directions of galaxy clusters involved. This largest and one of the most complicated collisions from galaxy clusters ever captured also confirm that the total mass concentration is mostly dark matter and it takes up roughly about 75% of the entire cluster collision map. These results conclude that dark matter constitutes most of the galaxy clusters and it is the invisible force that causes these collisions.
Galaxy clusters are the largest gravitationally bound objects in the Universe and it has become the most powerful tool in cosmology studies especially in the quest of finding and understanding the mysterious substance such as dark matter. These discoveries had given astronomers a foundation to progress further on finding the truth behind the ominous energy of dark matter. Astronomers have also depicted that dark matter is the mysterious force that shaped clusters of galaxies including our own Milky Way. According to the Chandra X-ray Observatory in the article “Evidence for Dark Matter”, Galaxies must contain about five to six times as much mass in dark matter as the amount of mass in gas and stars in order to provide the necessary gravity (Evidence, 2012). There are examples all around the entire Universe to adequately prove this, the same concepts are found in Dwarf galaxies as well as cluster of galaxies. Dwarf galaxies are usually faint containing only a few millions of stars but astronomers found it playing the main role in understanding dark matter. Despite the few numbers in stars and little gas, Dwarf galaxies manage to hold its shape rather than shooting stars out of its conventional orbit. This is primarily due to the function from dark matter since Dwarf galaxies do not contain enough stars or the gas to generally provide enough mass. This proves that Dwarf galaxies require a much larger amount of dark matter than normal galaxies. For clusters of galaxies, the scale multiplies by hundreds and sometimes even in thousands. In 1933, a scientist named Fritz Zwicky discovered that there is 10 to 100 times more matter than what could be found in stars that was needed to keep the galaxies clusters from flying apart. This is evidence that there is a very large amount of dark matter known as “missing matter” (in Zwicky’s time) present in cluster galaxies. Evidence found more recently by NASA also confirms that an abundance amount of dark matter does exist in galaxy clusters. According to the article “NASA Finds Direct Proof of Dark Matter” released on August 21, 2006, the galaxy cluster 1E 0657-556 also known as the "bullet cluster" formed after the collision of two large clusters of galaxies, it was one of the most energetic event known (recorded in human history) in the universe since the Big Bang. The Chandra X-ray telescope detected very large amounts of hot gas in the two pink formations that looks like a shape of a bullet (refer to figure 2.1). These two pink formations contain most of the baryonic matter, the blue areas on the other hand contain most of the mass in the whole cluster formation. This mass concentration was also detected by using the effect of gravitational lensing. Information gathered from the bullet cluster also suggests that the Universe consists of abundance amounts of dark matter.
All the information and data that have been gathered throughout the ages has led astronomers and scientists to conclude that the Universe is made up of many extraordinary and interesting substances. Dark matter, an abundance amount of subatomic particles that makes up a large percentage of the Universe is responsible for the behavior of cluster of galaxies, independent galaxies like our own, the Milky Way. As technology evolved, scientists’ understanding of this mysterious force also evolved. The discoveries of this “missing matter” changed the very fabric of our stellar understanding concepts and will continue to do for generations. Future discoveries of the true function and influence of dark matter will finally unravel its use so that astronomers can utilize it and completely understand the cosmos.

(Figure 1.0 Oldest light in the universe)
The amount of dark matter in the universe before galaxies formed can be determined from a study of the fluctuations (bright blue and red areas) in the cosmic microwave background radiation. (Credit: NASA/WMAP) (Figure 1.1) This chart represents the census of the Universe only 380,000 years after the Big Bang.
(Illustration: NASA/CXC/M.Weiss) RED: Hot Gas.
BLUE: Dark Matter.
(Figure 2.0) Abell 2744 Labeled (Figure 2.1) STScI-PRC2006-39a
RED: Hot Gas
BLUE: Dark Matter Reference
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Retrieved from: http://chandra.harvard.edu/photo/2011/a2744/
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Retrieved from: http://hubblesite.org/newscenter/archive/releases/2012/10/full/
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Retrieved from: http://chandra.harvard.edu/xray_astro/dark_matter/index2.html
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Retrieved from: http://hubblesite.org/newscenter/archive/releases/2006/39/image/a/