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Summary of Chapter 8: The Search

2021-01-07 来源: 51Due教员组 类别: Essay范文


下面为大家整理一篇优秀的essay代写范文 --Summary of Chapter 8: The Search,文章描述在黑洞如何形成的理论框架建立之后,物理学家和天文学家的任务就是从太空中寻找证据。首先,由于太空的广阔和搜索的难度,科学家需要用范围来确定寻找的地点。显然,成功的最高机会是在观测点尽可能接近地球上的观测者的地方。地球上没有黑洞,因为它们产生的巨大引力会显示出天体受到干扰的迹象,而这种干扰从未被观测到。根据黑洞的质量估计,离地球最近的黑洞估计至少有4光年远(Lena等人,2014)。

After the establishment of the theoretical frameworks of how a black hole forms, it became the task for physicists and astronomers to find evidence from space. First, due to the vastness of space and the difficulty of the search, scoping is needed for scientists to determine where to look. Obviously, the highest chance of success is where the point of observation is as close as possible to the observers on earth. There are no black holes on earth since the enormous amount of gravity they generate would show signs of disturbance on the celestial bodies, which is never observed. Estimating from the mass of a black hole, the nearest black hole to earth is estimated to be at least 4 light years away (Lena, et al, 2014).

The second difficulty posed in the search is in what way can an object so distant from earth be observed. Optical observations are infeasible since it is beyond the resolution of the best telescope on earth. The attempt to observe the disturbance of light emitted by the stars due to the black hole will fail as well, since the magnifying effect of a black hole is too minimal to be detected. Besides, such influences can be caused by both a black hole and a huge star, which scientists won’t be able to distinguish if the star is dim. One theory that is hopeful in the search is by looking for a two-body system that consists of a black hole and a star. The motion of the system is a constant rotation of the two bodies, which means that the star in the system would move closer and then further from the observer in a periodic way. The light, with is a form of electromagnetic wave, will show Doppler effect with periodic red shifts and blue shifts (Moreau, 1985). Finding these stars will create a pool which significantly refines the search process.

The pool already existed in the decades of observations by astronomers. After filtering and analyzation within it, eight potential candidates were selected by Virginia Trimble in 1968. Unfortunately, there are always other assumptions explaining why the other object in the two-body system is a very dim star, instead of a black hole. Another idea to search for black holes was proposed by Edwin Salpepter. When a black hold passes through a cloud of gas, the gas will be accelerated to the speed close to that of light. The gas would revolve around the edge of the black hole. The sudden increase in the density of the gas would turn the energy in the gas into hear, causing intense radiations surround the black hole. Comparing to a machine that burns fuel, the efficiency of the “black hole gas engine” is even higher.

After years of development in theory for this idea, scientist had realized that they would combine the ideas of the two-star system and the gas engine together in the search. The star in the system serve as convenient sources of gas to be captured by the other body, the black hole. The search also required an upgrade in the equipment used. In addition to the optical telescopes, it was found that large amounts of X-Ray would also be emitted in the radiating process of a black hole. A basic characteristic of the black hole is finally decided, which became the key to the search: a black hole is dim on the optical phases, and very bright in the X-Ray frequencies. Since X-Ray is not able to penetrate through our atmosphere, the observation has to be made using eyes in space. After decades of efforts and failures, the outer-space telescope system able to observe X-Ray was finally established by the 1950s.

The first direct and conscious observations of X-Ray by humans showed astounding results: the strength of X-Ray detected was 5000 times stronger than the expectations of scientists. It was later found out that the mistake was originated from the subject of study: the focus of the scientists had been on radiation from the Moon, planets and the stars. However, the major source of X-Ray radiation detected was due to the gas radiation caused by a black whole. The radiation source was found to be the Scorpio X-1. In 1962, Giacconi used an extremely simple yet effective experiment to reconfirm the observations. The measuring of a Geiger counters was recorded in different orientations, when it was pointed to the Scorpio X-1 direction, the recordings showed much high level of radiation (Giacconi, 2009). However, the true identity of the radiation source was yet to be confirmed.

More, and better X-Ray detectors were sent into space in the following decade, and the precision level increased to 300000 times compared to 16 years before. Other candidates are also found by the X-Ray detectors, including the Cygnus X-1, and the search was becoming more and more hopeful. Huge amounts of efforts were made in the 60s and 70s to confirm it. A more comprehensive theoretical background was also built surrounding the search and confirmation of the first black hole, including X-Ray radiation models of the gas combined with the observations. The confidence of the scientist in confirming the identity of the Cygnus X-1 increased from 80% in 1974, to 95% in 1995.

The effort continues, with the cooperation between physicists and astronomers. By the late 90s, it is almost completely confirmed that not only at Cygnus X-1, but also many other two-body systems within our galaxy, black holes physically exist.

References:

Giacconi, R. (2009). History of X-ray telescopes and astronomy. Experimental Astronomy, 25(1-3), 143-156. doi:10.1007/s10686-009-9139-8

Lena, D., Robinson, A., Marconi, A., Axon, D. J., Capetti, A., Merritt, D., & Batcheldor, D. (2014). recoiling supermassive black holes: A search in the nearby universe. The Astrophysical Journal, 795(2), 146. doi:10.1088/0004-637X/795/2/146

Moreau, N. (1985). Sound waves and stars: The doppler effect Library Journals, LLC

Thorne, K. S. (1994). Black holes and time warps: Einstein's outrageous legacy. New York: W.W. Norton.

 

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