The changes that occur during a star’s life are called stellar evolution. The mass of a star determines the ultimate fate of a star. Stars that are more massive burn their fuel quicker and lead shorter lives. Because stars shine, they must change. The energy they lose by emitting light must come from the matter of which the star is made. This will lead to a change in its composition. Stars are formed from the material between stars, shine until they exhaust their fuel, and then die a predictable death based upon their initial mass.
From atoms to stars Understanding of the processes of stellar evolution came as a result of twentieth century advances in both astronomy and atomic physics. Advances in quantum theory and improved models of atomic structure made it clear to astronomers that deeper understanding of the life cycle of stars and of cosmological theories explaining the vastness of space was to be forever tied to advances in understanding inner workings of the universe on an atomic scale.
In addition, a complete understanding of the energies of mass conversion in stars was provided by German-American physicist Albert Einstein’s (1879-1955) special theory of relativity and his relation of mass to energy (E = mc2, or energy [E?] equals mass [m] times the speed of light [c] squared). Indian-born American astrophysicist Subrahmanyan Chandrasekhar (1910-1995) first articulated the evolution of stars into supernovae, white dwarfs, and neutron stars; and predicted the conditions required for the formation of black holes, which were subsequently confirmed by observation in the last years of the twentieth century.
Stellar mechanics The material between stars occurs in clouds of varying mass. By processes that are still not completely clear, but involve cooling of the cloud-center with the formation of molecules, and the squeezing of the cloud by outside starlight or perhaps astellar explosion, the cloud begins to collapse under its own self-gravity. The collapse of the cloud results in the material becoming hotter simply from the squeezing of the collapse. At this point, the interior of the star churns. This churning process is called convection. Its rate of collapse is determined by the rate at which it can lose energy from its surface.
Atomic processes keep the surface near a constant temperature so that a rapid collapse is slowed by the radiating surface area shrinking during the collapse. The star simply gets fainter while the interior gets progressively hotter. Finally, the internal temperature rises to the point where atoms located at the center of the star, where the temperature is the hottest, are moving so fast from the heat generated that they begin to stick together. This process is called nuclear fusion, and it results in an additional production of energy. Thus, the star has a new source of heat.
The subsequent evolution of the star will be largely determined by its mass. If the mass of the star is about equal to that of the Sun or less, the nuclear fires that now provide the energy for the star to shine will determine its internal structure. A central radiative core is surrounded by a convective envelope. In the radiative core the material remains quiescent, while energy generated by nuclear fusion of hydrogen to helium simply diffuses through it like the light from automobile headlights shines through a fog. It is at the very center of this radiative core that the helium ash of the nuclear fires accumulates as the star ages.
Beyond the radiative core lies the churning convective envelope through which the energy is carried by blobs of hot matter rising past returning cooler blobs. At the atmospheric surface, the energy again flows as it did in the core until it physically leaves the star as starlight. The structure of stars more than twice the mass of the Sun is essentially the reverse of the low-mass stars. The cores of these stars are fully convective so that the energy produced by nuclear fusion is carried outward by the churning motion of the material in the core.
The surrounding radiative envelope behaves much like the cores of lower-mass stars except no new energy is produced there. The churning motion of the material in the convective core causes the nuclear ash of helium to be mixed with the surrounding hydrogen fuel. This motion ensures that virtually all the hydrogen will be available to the nuclear fires that heat the star. Both high- and low-mass stars respond to the depletion of hydrogen fuel in a similar manner. In order to supply the heat to oppose its own self-gravity, the star’s core again responds by shrinking.
In a sort of reflex reaction, the outer regions of the star expand, causing a great increase of its radiating surface area. Although the total energy output of the star increases during this phase, the greatly enhanced surface area results in a cooling of the surface and the star takes on a redder appearance. The size and color change lead to the name of red giant for these stars. If the star is very massive, it may become what is called a red supergiant. For the low-mass stars, the expansion to the red giant phase will begin when about 90% of its hydrogen has been converted to helium.
During the contraction of its core, a complicated sequence of events occurs. The shrinkage required to produce the energy radiated by the large giant causes the core to shrink to the dimensions of a white dwarf, while hydrogen continues to burn by nuclear fusion in a thin shell surrounding the core. This shell provides most of the energy that is radiated away by the star. However, the core material, having attained the dimensions of a white dwarf, behaves very differently than the high-density gas that it was earlier in its life. No longer must it be heated to generate the pressure required to oppose the weight of the overlying material.
When matter reaches this state, it is called degenerate matter. The degenerate core just sits there, becoming hotter from the energy released by the surrounding hydrogen-burning shell and growing slowly from the helium ash generated by the shell. The hydrogen-burning shell is required to produce increasing amounts of energy from decreasing amounts of hydrogen fuel to sustain the brightening red giant. This continuing increase in the energy output from the shell heats the core, which finally reaches a temperature where the helium begins to undergo nuclear reactions, producing carbon.
In this fusion process, three helium nuclei collide yielding one carbon nucleus and additional energy for the support of the star. The star now has a new energy source. However, the degenerate nature of the core does not allow it to expand and cool as would a core made of ordinary gas. Thus, the onset of helium burning leads to a rapid rise in core temperature, which is not balanced by a cooling expansion. The increased core temperature leads to a dramatic increase in helium burning. This sequence, known as the helium flash, continues until the degeneracy of the material making up the core is removed by the intense heat.
The return of the material to its ordinary gaseous state leads to a rapid expansion, which cools the core and reduces the helium burning. An equilibrium is established with the star generating progressively more energy from helium fusion, while the energy from the hydrogen burning shell is reduced, and it ultimately goes out from lack of fuel. The star continues to shine through the red giant phase by converting helium into carbon through nuclear fusion. As the helium becomes depleted, the outer layers of the star become unstable and rather gently lift off the star to be slowly blown away by the light from the star. Such an image was captured in 1998 by the Hubble Space Telescope when a dying star known as NGC7027, located about 3,000 light-years from the Sun in the direction of Cygnus the Swan, was observed. ) Such shells of expanding gas are observed as greenish disks that eventually become greenish rings and the material becomes less dense. These greenish clouds are called planetary nebulae, even though they have nothing whatever to do with planets. Astronomers of two centuries ago gave them that name, for their telescopic appearance from the Earth was like that of the outer planets Uranus and Neptune.
The remaining core of the red giant, now exposed, cools rapidly, again becomes degenerate, and is known as a white dwarf. A white dwarf has reached a stalemate between its own self-gravity and the nature of the degenerate stuff of which it is now composed. It may now simply cool off to become a dark stellar cinder about the size of the Earth. The evolution of a massive stars follow a somewhat different course. The churning of the convective core makes most of the hydrogen fuel available for consumption in the nuclear fires. Thus, these stars will not suffer the effects of core contraction until more than 99. % of their hydrogen has been consumed. Even though they can consume more of their hydrogen (on a percentage basis), and they have more fuel to burn, they also shine much brighter than the low-mass stars. Thus, their overall lifetimes will be far less than the low-mass stars. While the lifetime of a star like the Sun may approach ten billion years, a star with ten times the mass of the Sun may last less than ten million years. The exhaustion of the hydrogen convective core leads to its contraction and the expansion of the outer layers, as was the case with the low-mass stars.
However, the fate of the core is rather different from that of the low-mass stars. The core is far too massive to reach equilibrium as a degenerate structure like a white dwarf, so that contraction continues heating the core until the ignition of helium fusion is achieved. Unlike the lower-mass stars where the onset of helium burning occurs with a flash, the helium fusion in massive stars begins slowly and systematically takes over from the hydrogen-burning shell surrounding the core. Throughout the red giant- or supergiant-phase the role of energy production steadily shifts from hydrogen burning to helium burning.
Eventually, helium becomes exhausted around a growing carbon core. While helium continues to undergo fusion in a shell surrounding the core, carbon fusion is ignited. Just as a degenerate helium core gives rise to the unstable ignition of helium, called the helium flash in low-mass stars, so the degenerate carbon core of moderate mass stars can result in an unstable ignition of carbon. However, whereas the helium flash is quickly quelled in low-mass stars, the carbon ignites explosively in the cores of these moderate-mass stars. This process is called carbon deflagration and may result in the destruction of the star.
In even more massive stars, the onset of carbon burning is a controlled process and the star develops multiple shells of energy sources involving carbon fusion, helium fusion, and even some hydrogen fusion in the outer regions of the star. The ignition by nuclear fusion of each new element yields less energy than the one before it. In addition, the increased temperature required for the nuclear fusion of these additional sources leads to an increase in the stellar luminosity. The result is an ever-increasing rate of the formation of less-efficient energy sources.
When nuclear fusion in the core of the star yields iron, further nuclear fusion will no longer yield energy. Instead, nuclear fusion of iron will use up energy-robbing thermal energy from the surrounding material. This sudden cooling of the core will bring about its collapse. As the density increases in the collapsing core, there is less and less room for the free electrons that have been stripped from the atomic nuclei by the extreme temperature. These electrons must go somewhere, so they begin to be absorbed in the protons of the atomic nuclei, turning them into neutrons.
The process is called neutronization. This reaction generates particles called neutrinos, which interact very weakly with ordinary matter, and so normally escape directly from the star. The energy robbed from the core by the neutrinos also adds to the energy crises in the core and contributes to the core collapse. The production of elements with masses greater than iron also produces large quantities of neutrinos, so that whichever process dominates, a great deal of energy is lost directly from the star, resulting in a catastrophic gravitational collapse of the core.
This action is followed promptly by the collapse of the entire star. The rapid increase in the density of the collapsing core finally reaches the point where the material becomes opaque to the energy-robbing neutrinos, and their continued escape is stopped. The sudden deposition of the neutrino energy in the collapsing core reverses the collapse, bringing about an explosion of unprecedented magnitude. The infalling matter and trapped photons are hurled into space, liberating as much energy in a few minutes as the star has radiated in its lifetime of millions of years.
The remains of this titanic explosion depend on the initial mass of the collapsing star. Very-massive stars may leave a black hole of completely collapsed matter behind. Should the collapse involve a star of less mass, the remainder may be something called a neutron star, similar to that formed by the collapse of a white dwarf. In some instances, the entire star may be involved in the explosion and there will be no remains at all. While there have been recent attempts to refine the classification of these explosions, astronomers still refer to the explosion of a massive star as a supernova of type II.
Supernovae of type I are thought to result from the collapse of a white dwarf, which has exceeded its critical mass. Unlike the evolution of low-mass stars, in which an accommodation between the forces of gravity and degenerate structure of the star is achieved through the formation of a white dwarf, the evolution of a massive star must end in a violent stellar explosion. Gravity appears to win its struggle with nuclear physics, but at the last moment, the energy of collapse is turned to an explosion leaving either a collapsed corpse, or perhaps nothing at all.
The accession of the Hubble Space Telescope had given astronomers a valuable tool to study the evolution of stars in the universe, at the same time challenging their understanding. In 1997, Hubble detected rogue stars that do not belong to any galaxy, displaced long ago and now hanging in empty intergalactic space among star clusters like the Virgo Cluster, about 60 million light-years from the Earth. In 1996, astronomers found evidence of many isolated, dim brown dwarfs, lacking sufficient mass to start nuclear fusion. They detected light spectra from the element lithium, which quickly burns in true stars.
These brown dwarfs, called L dwarfs, are typically smaller then the sun but much larger than even Jupiter, and some may resemble Saturn’s moon Titan. On the opposite scale, in 1997, Hubble detected the then brightest star ever seen. Discovered at the core of the Milky Way galaxy and named the Pistol star, it has the energy of ten million Suns and would fill the distance of the Earth’s orbit around the sun. The Pistol Star is about 25,000 light-years from the Earth; it is so turbulent that its eruptions create a gas cloud four light-years across.
It had been thought that a star so big could not have formed without blowing itself apart, and so the Pistol Star will require astronomers to reexamine their ideas about stellar formation, especially of supermassive stars near the centers of galaxies. By 2003, other observations, including x-ray observations from the ROSAT (short for Rontgensatellit) Observatory and NASA’s Chandra X-ray Observatory (CXO), allowed the identification of high intensity ultra-bright x-ray sources that many astronomers argued were evidence of black holes in star-forming galaxies.
Although there are other explanations for these phenomena, the fact that they provide additional confirmation of black holes is enhanced by Hubble observations of stars rotating around stellarcores of these galaxies. In early 2003, the Chandra X-ray Observatory, provided extended observations of Sagittarius A (or Sgr A), the supermassive black hole at the center of Earth’s own Milky Way galaxy. In 2004, astronomers found over 30 black holes.
In fact, a black hole was discovered in June 2004 that scientists conjecture will help to confirm that gigantic black holes were created early in the formation of the universe. In 2005, a black hole was discovered to be traveling at twice the escape velocity of the galaxy as it exited the Milky Way. Scientists think that such a black hole may help to support the theory that a black hole exists in the center of the Milky Way galaxy.
A Flight That Changed My Life
While some may not consider it remarkable, the act of boarding my first flight deeply impacted my perspective on life. It marked the beginning of an amazing journey as my family and I moved to a foreign country, which had never been a thought in my mind before. In just 24 hours on that plane, this flight completely transformed my existence by introducing me to an entirely different way of living.
In 2006, my family and I made the decision to move abroad during winter. Before our departure, my mother informed me that she, my brother, and I were going to immigrate to the United States of America in search of better opportunities. At just 14 years old, I had no knowledge of what awaited me in the U.S., but I was incredibly excited about traveling overseas for the very first time. Time passed swiftly, leaving little opportunity for me to bid farewell properly to my friends and most importantly, my beloved great grandmother.
I eagerly anticipated boarding my first flight, excited to see my motherland from above. This journey was meant to provide a better life for my family, yet tears welled up for unknown reasons. Perhaps I was scared or missed my old home. Regardless, I let go of any tears and embarked on the plane with my family. In August 2006, at nighttime, our plane landed at the International Airport of Houston. Stepping off the plane, I knew that a whole new destiny awaited me, and I understood that my life would be completely transformed.
The impressive skyscrapers and the new climate of the city greatly inspired me. Witnessing the immense buildings and bright city lights of a highly developed country, I made a promise to myself that I would learn how to create such marvels in the future. I fell in love with my new home due to its winter weather and modern technology, both completely new experiences for me. Additionally, I committed myself to achieving my goals and ultimately living on the top floor of a skyscraper.
Upon receiving my immigration document, I immediately started school without much time to rest or explore the town. As someone with limited knowledge of English, starting school felt like being lost in the Amazon forest. However, I transformed from a non-English speaker into someone who can now speak and understand most English. Over the next few years, my life gradually changed as I adapted to my new environment. That flight had transformed me into an improved person with a promising future.
Living in this city has been truly transformative for me.
S, I almost lost my motivation due to the individuals I used to associate with. However, I transformed this situation into an opportunity to remain focused on the positive changes and committed to reaching my goals.
Coming to the U.S. has given me a new beginning and exposed me to a completely different world. I have managed to maintain a positive mindset while constantly remembering where I come from.
Over time, I have noticed significant changes within myself. My determination remains strong as I work towards proving that these transformations will ultimately lead me to success in the future.
Living and studying in a country known for its exceptional education has given me an invaluable chance to pursue my dreams and goals. This experience has greatly impacted the person I am today, teaching me to seize every opportunity for personal growth. Without taking that initial leap, I can’t even fathom who I would be now. Despite encountering difficult situations, I have maintained my determination and remained focused on the positive changes in my life. Constantly reminding myself of my immigrant status provides me with the resilience and motivation needed to keep striving towards my aspirations.
King John And Magna Carta
1. How did religion influence the Magna Carta? King John of England had unlimited power and was taking large amounts of money without consulting his nobles. Magna Carta is a document that was created to stop the King from abusing his nobles. According to this document anything related to God is exempt from this rule. 2. How did the Magna Carta limit the power of King John? King John was forced to signed the Magna Carta document. This greatly reduced his power. He couldn’t collect large amounts of money and abuse the system.
3. How did the Magna Carta lay the foundation for democracy? This document of Magna Carta which was created in 1215 to stop the abuse of King John and to help the citizens rights. The King himself had to obey the laws and so it gave everybody equal opportunities Document B 1. How much influence do you think pastors had on society during the Middle Ages in Europe? Explain. In the medieval ages in Europe pastors had a great influence on the society. They were considered to have a third kind of life called next life and were considered superior over other men or women. . What is the mixed life? In Middle Ages Prelates who were considered highly ranked clergies and pastors had a third kind of life called the mixed life. They were considered to be superior and preached men and woman about body and souls. 3. To lead the mixed life, do you think a prelate or pastor would spend time in a monastery? Explain. To lead a mixed life Prelates and pastors should be away from external business and to be involved in praying, meditation, reading holy scriptures, and following spiritual exercises. So they should spend time in a monestry.
Document C 1. How does this painting show the influence of religion on politics? This picture shows Joan of Arc holding flags that have pictures of angels on them. This shows that she is very religious. She is also wearing suit suit of armor which signifies that she wants to be involved politically 2. Do you think the painter of this picture viewed Joan of Arc as a heroine? Explain. I think the painter be viewed Joanna of Arc as a heroine. The picture shows Joan or Arc wearing a suit of armor showing she’s a hero. She was determined to drive the English out of France.
She did succeed in doing this and so she became a heroine. 3. How does this painting combine the style of the ancient Greeks and Roman artists with that of the artists of the Middle Ages? Give examples. In the late Middle Ages paintings were mainly of humans as the central subject without much dramatic action. Religious symbols were common in this picture shows Angels on the banners. In those times the painters did not make the pictures look exactly like people giving the painting the sense of depth. Document D 1. How do you think Pope Urban II and the Crusades influenced the trade routes shown on this map?
The Crusades which were the Holy Wars contributed to increasing trade in Europe. Many routes for Pilgrims were opened and there was large increase in spice trade in Eastern Asia. The Crusades also improved navigation techniques. 2. Which cities shown on the map do you think were most affected by ideas from foreign lands? hich cities were least affected by ideas from foreign lands? Explain. The cities that were most affected are Frankfurt, London, and Paris. 3. What cities seemed to benefit the most from trade routes by sea? Explain. Some of the cities were Visilby, Vienna, Florence, Rome, Basel, Genoa, and Frankfurt Document E . Do you think the social standing of merchants during the Middle Ages helped or hurt the economy? Explain. In the feudal system the Kings own most of the land and they were very powerful. They gave some land to the nobles who served the Kings.
The night protected the nobles and in exchange got some land. Merchants were in cities and not involved in the land exchange. This hurts the economy. 2. Do you think church officials had a large amount of influence in the feudal system? Explain. Church officials by themselves owned pieces of land. Church officials have influence on the feudal system as their religious people. . In the feudal system, do you think knights ever felt conflicting loyalties? Explain. Knights got a peace of land for protecting the Nobles. So in the feudal system the knights have to be loyal to the nobles to earn some land. Document F 1. Do you think the social standing of merchants in feudal Japan helped or hurt the economy? Explain. Japanese feudal society, the merchants Help the economy. They had a much higher status than in feudal Europe. The Japanese feudal merchants did own their own land that they cultivated. They were respected as they produced food for people. 2.
How is feudalism in Japan similar to the feudalism in Europe? How is it different? In the European feudal system the kings were very high in position. The Lords and the Japanese feudal system had armies and often more powerful. This is how they were similar. But in the European feudal system there was not one Lord that ruled the region. In the European feudalism the nights were granted some land from the king and exchange for the kings protection. However, in the Japanese feudal system the samurai never owned land. In the Japanese feudal system the peasants owned land and cultivated.
They were very well respected as they produced food. This is different from the European feudalism as merchants in the European feudal system did not own land. The artisans in the Japanese and European feudal system was similar, they were always in the lowest position socially and economically. 3. Do you think feudalism in Japan helped to unify the country? Explain. No it did not unify the country of Japan. The society was divided into seven levels. The Emperor who has the highest level had no power. Below the emperor was the Shogan who had the most power. Then there were vassals. This Shogan hired warriors for their protection.
Below the warriors were peasants, artisans, and merchants. 1. Based on this excerpt, do you think Buddhism had a widespread influence in Japan? Explain. The Buddhism had wide influence in Japan. The excerpt says that you need to be in association with good people. It also says to save mankind. 2. In medieval Japan, what do you think are some of the attributes of moral behavior? In medieval Japan Buddhism strives to save mankind and also should exert your mind to the highest in all of your activities. 3. According to Ryoshun, what negative influence should his brother try to avoid?
According to Ryoshun his brother should not be in company with bad people and try to help mankind. “In what ways did religion and economic influence the development of medieval Europe and Japan? ” Religion and economics had major impact on the development of medieval Europe and Japan. People of Europe and Japan were very religious people in the medieval period. There were Crusades which are holy wars to acquire the holy land of Jerusalem. Religious authorities like Prelates and Pastors were considered very superior. Trade also increased between countries which made some countries economically stable.
The feudalism in European and Japan also affected the economic status. In the medieval times there were Crusades which were religious wars to occupy the holy land of Jerusalem. This holy land is located at the intersection of three continents. Three religions Judaism, Christianity and Islam met in this holy land. Even though all three had common roots and had major conflicts. Initially the Christian pilgrims were allowed to visit the holy land, but later the Seljik Turks conquered the land and did not allow the Christians to visit. They had several holy wars called Crusades. The Crusades had several outcomes.
Several churches were built, several routes were opened for trade and people were spending money. Trade between countries was also increased for example spice trade from East Asia. Joan of Arc was born in 1412 in a French Village. When she was 13 she began to hear voices telling her to devote her life to God and to save France. So she went to the higher authorities and asked them to give her a troop of soldiers and she would see that the English left France. Her request was granted and she was given army, a suit of armor and a white banner. Just as she told the king she was succeeded in freeing the France from English.
After this she was consider a heroine. Magna Carta was a document signed by King John of England to stop him from abusing his nobles. During the 1100s, the king was in power and was demanding huge amounts of money without talking to his nobles for before making decisions. Some nobles did not like the King’s actions and did not support him. The King was forced to sign the document Magna Carta which was written to protect the citizen’s rights. During the Middle Ages there was Feudalism in Japan and Europe. There were several classes of people according to this system. The King was the highest authority in the European Feudalism.
He had large areas of land. The nobles served the King and got land in return. The Church Officials had land of their own. The Nobles gave the Knights some land as they protected them. The Merchants, Artisans, and Peasants had no land. The religion of Buddhism taught people of Japan to be close to good people and to help each other. In conclusion economic and religion played a huge role in Medieval Europe and Japan. Some religious acts like the Crusades increased trade and economic conditions of the countries. Feudalism also had impact on the economic status on Europe and Japan. People also were very religious and did good deeds.