By: MenWei Weng
Submitted to Professor: Peter Luca
Introduction Our universe contains more than one trillion galaxies, each of them may contain with billions of stars, dust and clouds of gas, and perhaps many planets are similar to the planets in our solar system. The stars produce a lot of energy, from radio waves to X-rays. Some of the stars may even reflect the energy, like how the moon reflects sunlight, which the energy across the universe at the speed of light at the end. Yet, everything that we see is just a tiny bit of the universe, it accounts only for about four percent of the total mass and energy in the universe. About seventy-four percent of the universe consists of dark energy and twenty-one percent for dark matter. “In brief, dark matter attracts, dark energy repels. While dark matter pulls matter inward, dark energy pushes it outward.”
Does dark matter really exist? Since early 1980s, dark matter had become commonplace. The cosmologists from the Sloan Digital Sky Survey, the SLACS team have so far isolated 98 elliptical and spiral galaxies that have moderately high redshift (Bolton et al. 2008)4. Which SLACS discovered that galaxies in clusters, the gravitational lensing of background objects, and the observed fluctuations in the cosmic microwave background radiation require the presence of additional gravity, which can be explained by the existence of dark matter3, 4.
What is dark energy and dark matter?
For now we only know how much dark energy there is because we know how it affects the universe’s expansion. Other than that, it is a complete mystery. There are still many arguments of how dark energy affects the universes, which cosmologists has come up with many versions of explanation of dark energy. One of the most popular explanations is “Einstein’s gravity theory”4, the version that contains a cosmological constant, “makes a second prediction: empty space can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear. As a result, this form of energy would cause the Universe to expand faster and faster. Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the Universe.”1, 2, 4
The nature of dark matter is unknown. For now, we only know that the universe contains twenty-seven percent of dark matter. It is not in the form of stars, planets, and dust and dark clouds of normal matter, or any matter that we can detect like baryonic, protons and neutrons. Since we cannot see the unique gamma rays that are produced when antimatter annihilates with matter, we are able to tell that dark matter is not antimatter. Cosmologists believe that dark matter are formed when the universe was a fraction of a send old, and mostly composed of exotic particles. Such particles could be as WIMPs (Weakly interacting massive particles) 2, 3, 8, or sterile and neutrinos.
What is the role of dark matter in galaxy formation? The dark matter has been grown, since the first few hundred thousand years after the big band, which it cost to result in the formation of galaxies that we see. During the formation of galaxy, dark matter halos provide most of the gravitation to help galaxy stable structures formed in the universe3. During the pass few epochs, we have found that dark matter halos preserve these clusters, galaxies and groups as the dark energy tears apart unbound structures and expands the space between bound structures such as the Local Group of galaxies4. For example, the Virgo Cluster of galaxies (about 60 million light-years away) 4 appears to be tugging on the Milky Way and other galaxies of the Local Group. This gravitational tug may eventually reverse the