Formation and Evolution Essay Example for Free

Formation and Evolution Essay A black hole is a theoretical region of space in which the gravitational field is so powerful that nothing, not even electromagnetic radiation (e. g. visible light), can escape its pull after having fallen past its event horizon. Black holes are objects so dense that not even light can escape their gravity, and since nothing can travel faster than light, nothing can escape from inside a black hole. On the other hand, a black hole exerts the same force on something far away from it as any other object of the same mass would. For example, if our Sun was magically crushed until it was about 1 mile in size, it would become a black hole, but the Earth would remain in its same orbit. Even back in Isaac Newtons time, scientists speculated that such objects could exist, even though we now know they are more accurately described using Einstein’s General Theory of Relativity. Using this theory, black holes are fascinating objects where space and time become so warped that time practically stops in the vicinity of a black hole. The former types have measured masses ranging from 4 to 15 Suns, and are believed to be formed during supernova explosions. The after-effects are observed in some X-ray binaries known as black hole candidates. On the other hand, galaxy-mass black holes are found in Active Galactic Nuclei (AGN). These are thought to have the mass of about 10 to 100 billion Suns. The mass of one of these super massive black holes has recently been measured using radio astronomy. X-ray observations of iron in the accretion disks may actually be showing the effects of such a massive black hole as well. Formation and Evolution The primary formation process for black holes is expected to be the gravitational collapse of heavy objects such as stars, but there are also more exotic processes that can lead to the production of black holes. Gravitational collapse occurs when an objects internal pressure is insufficient to resist the objects own gravity. For stars this usually occurs either because a star has too little fuel left to maintain its temperature, or because a star which would have been stable receives a lot of extra matter in a way which does not raise its core temperature. In either case the stars temperature is no longer high enough to prevent it from collapsing under its own weight. The result is one of the various types of compact star. Which type of compact star is formed depends on the mass of the remnant the matter left over after changes triggered by the collapse (such as supernova or pulsations leading to a planetary nebula) have blown away the outer layers. If the mass of the remnant exceeds ~3-4 solar masses (the Tolman-Oppenheimer-Volkoff limit)—either because the original star was very heavy or because the remnant collected additional mass through accretion of matter)—even the degeneracy pressure of neutrons is insufficient to stop the collapse. After this no known mechanism (except maybe the quark degeneracy pressure, see quark star) is powerful enough to stop the collapse and the object will inevitably collapse to a black hole. This gravitational collapse of heavy stars is assumed to be responsible for the formation of most (if not all) stellar mass black holes. Once a black hole has formed, it can continue to grow by absorbing additional matter. Any black hole will continually absorb interstellar dust from its direct surroundings and omnipresent cosmic background radiation, but neither of these processes should significantly affect the mass of a stellar black hole. Properties of Black Holes According to the No Hair theorem a black hole has only three independent physical properties: mass, charge and angular momentum. Any two black holes that share the same values for these properties are indistinguishable. This contrasts with other astrophysical objects such as stars, which have very many—possibly infinitely many—parameters. Consequently, a great deal of information is lost when a star collapses to form a black hole. Since in most physical theories information is preserved (in some sense), this loss of information in black holes is puzzling. Black Hole Types The simplest possible black hole is one that has mass but neither charge nor angular momentum. These black holes are often referred to as Schwarzschild black holes after the physicist Karl Schwarzschild who discovered this solution in 1915. It was the first (non-trivial) exact solution to the Einstein equations to be discovered, and according to Birkhoffs theorem, the only vacuum solution that is spherically symmetric. The Reissner-Nordstrom solution describes a black hole with electric charge, while the Kerr solution yields a rotating black hole. The most general known stationary black hole solution is the Kerr-Newman metric having both charge and angular momentum. Sizes Black holes occurring in nature are commonly classified according to their mass, independent of angular momentum J. The size of a black hole, as determined by the radius of the event horizon, or Schwarzschild radius, is proportional to the mass through where is the Schwarzschild radius and is the mass of the Sun. Thus, size and mass have a simple relationship, which is independent of rotation. According to this mass/size criterion then, black holes are commonly classified as Super massive black holes, Intermediate-mass black holes, Stellar-mass black holes, Micro black holes Conclusion There is very good evidence from astronomical observations that the universe is full of black holes with sizes ranging from six to a billion solar masses in size. Black hole accretion power is responsible for some of the most spectacular phenomena in the universe. These phenomena are NOT well understood, however, largely because of the complexity of the physics of the central accretion flow. There is little doubt, though, that black holes exist at the heart of active galactic nuclei, quasars, and certain X-ray binaries. Accretion power is an important contributor to the overall evolution and ecology of the universe. Electromagnetic observations are currently probing the innermost parts of accretion flows, and revealing interesting effects of the relativistic space-time assuming our models of the flows are not WAY wrong. How can one prove the existence of black holes, short of a suicidal leap across an event horizon? Detection of gravitational waves ripples in the fabric of space-time itself, is perhaps the only way. Currently astronomers view black holes if they are lit up electromagnetically a very biased view! Black holes which are lit up gravitationally may offer a very differently biased view. Works cited Kraus, Ute. Step by Step into a Black Hole. (2005-03-20) Remillard, Ronald A. ; McClintock, X-ray Properties of Black-Hole Binaries, Ann. Rev. Astron. Astrophys. (2006) 44: 49–92. Celotti, A. ; Miller, J. C. ; Sciama, D. W. , Astrophysical evidence for the existence of black holes, (1999) Class. Quant. Grav. 16. Hawking, S. W. ; Penrose, R. , The Singularities of Gravitational Collapse and Cosmology, (1970) Proc. Roy. Soc. Lon 314 (1519): 529–548 Schwarzschild, Karl , Uber das Gravitationsfeld eines Kugel aus inkompressibler Flussigkeit nach der Einsteinschen Theorie(1916), Sitzungsber. Preuss. Akad. D. Wiss. : 424–434.

Characters, Themes and Imagery in Their Eyes Were Watching God Essay ex

Characters, Themes and Imagery in Their Eyes Were Watching God      Ã‚  Ã‚  Ã‚  Ã‚   Zora Neale Hurston was one of the first widely acclaimed black writers to "assimilate folk tradition into modern literature and express her interpretations of the black culture throughout her books" (Bailey, 175).   She was also one of the most influential of black American writers during the twentieth century because she exceeded the barriers of race, sex and poverty.   Hurston's most acclaimed work is said to be Their Eyes Were Watching God, and has been read, adored, rejected, reviewed, and badgered by many literary critics.   "In a book rich with imagery and black oral tradition, Zora Neale Hurston tells us of a woman's journey that gives the lie to Freud's assertion that 'the difficult development which leads to femininity seems to exhaust all the possibilities of the individual'" (Morgan, 163).   In this as well as in other of her writings, Hurston expresses many of her opinions of race relations, sexism, and classism through her characters, themes and imagery.    The novel, Their Eyes Were Watching God focuses on a character named Janie who is raised by her grandmother on a white plantation in Georgia, and until seeing a photograph of herself, she has always assumed that she is white.   She loves her grandmother, but after her grandmother's death, she realizes that she resents her as well.   Her grandmother has been strict with her and has taught her that love is obtained only through marriage.   Janie feels that her grandmother has taken all of her dreams away.   Although she is independent, Janie marries three times.   Because of her grandmother she marries Logan Killicks, who works Janie so hard that she decides to leave.   Then she meets Joe Star... ...ir Eyes Were Watching God. New York: Bloom's Literary Criticism, 2008. Print. Dawson, Emma J. Waters. Images of the Afro-American female character in Jean Toomer's Cane, Zora Neale Hurston's Their Eyes Were Watching God, and Alice Walker's The Color Purple. Michigan: UMI Dissertation Information Service, 1990. Hurston, Zora Neale. Their Eyes Were Wagvtching God: A Novel. New York: Perennial Library, 1990. Print Kubitschek, Missy D. "`Tuh de Horizon and Back': The Female Quest in Their Eyes Were Watching God." BALF 17.3 (Fall 1983): 109-15. Morgan Grant, Alice. ed. All About Zora: Views and Reviews by Colleagues and Scholars. Florida: Four-G Publishers, Inc., 1991. Wall, Cheryl A. "Zora Neale Hurston: Changing Her Words," American Novelists Revisted: Essays in Feminist Criticism. Ed. Fritz Fleischmann, New York: G.K. Hall and Co. 1982:371-93.   

Alex Robbins.Durango Street

Durango Street Reading Log for Chapters 15, 16, 17 Character: Alex Robbins Alex Robbins is a social worker. His goal is to break up the gang â€Å"the moors†, but until chapter 17 he has no success. Alex Robbins is one of the main characters in the book, because he affects the gang â€Å"the moors†. In chapter 17 he is at Rufus’ home, because â€Å"The Gassers† cut the pigtail of Rufus’ sister. When Rufus comes home Alex Robbins is talking to his mother, that he wants to talk with â€Å"the Gassers† about what happened. But when Rufus asks about what happened, Alex tries to tell him a lie. But Rufus is smart and knows that he is telling a lie. After Rufus knows what happened, he is very angry and Alex sais that he wants to solve this issue, but Rufus sais that he has no idea of gangs. I think the idea of Alex is very absurd. In this case there is no way out. He can’t speak with the police, because it will make more problems. Alex also made a very inexperienced impression, when he talked the first time to â€Å"the moors†. Everybody laughed about him and he couldn’t accomplish himself. He seemed to be much untaught. He is a little bit the opposite of Rufus, who is very smart. Finally, I think Alex really wants to reach his goal to break up â€Å"the moors†, but he has to learn a lot, how to handle these guys.

Components Of An Educational Philosophy - 1038 Words

A person’s philosophy is defined as, â€Å"A theory or attitude held by a person that acts as a guiding principle for behavior.† If a person’s philosophy shapes his or her actions, then it is vital for any professional to have a good philosophy in their profession, so their actions follow suit. Therefore, it is important for an educator to have a solid philosophy of education so that his or her teaching is effective and right before God. Six important components of an educational philosophy are metaphysics, epistemology, axiology, the nature of the learner, the school, and the teacher. However, the foundation that holds up all six of these philosophical components in a strong christian educational philosophy is God. In philosophy, metaphysics is the study of what is beyond the physical realm. It questions being, knowing, causation, identity, etc. Genesis 1:2 tells us that, â€Å"The earth was formless and empty and darkness covered the deep waters. And th e spirit of God was hovering over the waters† (New Living Translation). Before there was anything, there was God. God is what is beyond the physical and he is the very essence of being. God describes himself to Moses by saying, â€Å"I am who I am† in Exodus 3:14. Again, God is expressing himself here as the greatest form of being. Nothing was, is, or will be in existence unless God is first. All of creation and human kind lives and breathes between those two words, â€Å"I am.† When it comes to metaphysics, God is the ultimateShow MoreRelatedEducators Struggle with Philosophy1075 Words   |  4 Pageswe all struggle with philosophy and where to go from there once we decide what our set of beliefs are. Once we put our philosophy in place, we then struggle with changing our philosophy. 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Perkins Act of 2006, consider the components that pertain to you and your subject/industry. Identify those components and expand on the direct relationship they have to your current or future classroom. What would you change or add, if you had the chance? What would you delete? Learning the historical and present legislationRead MoreThe s Views On Constructivism1347 Words   |  6 Pages This type of model has been tested but has not been successfully implemented. â€Å"The lack of success in implementing this widely accepted educational epistemology into the schools can be attributed to what might be called failures of readiness† Elkind (2004). In this quote he states that in order for constructivism to work successfully, three major components must be in place; teacher readiness, curricular readiness and social readiness. One of the few major problems with â€Å"teacher readiness† isRead More A Labor of Love Essay974 Words   |  4 Pagesprofessional objectives be achieved. 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