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Passage 33
  Until recently most astronomers1 believed that the space between the galaxies2 in our universe was a near-perfect vacuum. This orthodox view of the universe is  now being challenged by astronomers who believe that a(5) heavy “rain” of gas is falling into many galaxies from the supposedly empty space around them. The gas apparently3 condenses into a collection of small stars, each a little larger than the planet Jupiter. These stars vastly outnumber the other stars in a given galaxy4. The(10) amount of “intergalactic rainfall” into some of these galaxies has been enough to double their mass in the time since they formed. Scientists have begun to suspect that this intergalactic gas is probably a mixture of gases left over from the “big bang” when the galaxies were(15) formed and gas was forced out of galaxies by supernova explosions.
  It is well known that when gas is cooled at a constant pressure its volume decreases. Thus, the physicist5 Fabian reasoned that as intergalactic gas cools, the cooler gas(20) shrinks inward toward the center of the galaxy. Mean- while its place is taken by hotter intergalactic gas from farther out on the edge of the galaxy, which cools as it is compressed and flows into the galaxy. The net result is a continuous flow of gas, starting as hot gases in inter-(25) galactic space and ending as a drizzle6 of cool gas called a “cooling flow,” falling into the central galaxy.
  A fairly heretical idea in the 1970‘s, the cooling-flow theory gained support when Fabian observed a cluster  of galaxies in the constellation7 Perseus and found the(30) central galaxy, NGC 1275, to be a strange-looking object  with irregular, thin strands8 of gas radiating from it.
  According to previous speculation9, these strands were gases that had been blown out by an explosion in the  galaxy. Fabian, however, disagreed. Because the strands(35) of gas radiating from NGC 1275 are visible in optical photographs, Fabian suggested that such strands consisted not of gas blown out of the galaxy but of cooling flows of gas streaming inward. He noted10 that the wavelengths11 of the radiation emitted by a gas would changes as the(40) gas cooled, so that as the gas flowed into the galaxy and became cooler, it would emit not x-rays, but visible light, like that which was captured in the photographs. Fabian‘s hypothesis was supported by Canizares’ determination in 1982 that most of the gas in the Perseus cluster was at a(45) temperature of 80 million degrees Kelvin, whereas the gas immediately surrounding NGC 1275 (the subject of the photographs) was at one-tenth this temperature.

  1. The primary purpose of the passage is to
   (A) illustrate13 a hypothesis about the origin of galaxies
   (B) provide evidence to dispute an accepted theory about the evolution of galaxies
   (C) summarize the state of and prospects14 for research in intergalactic astronomy
   (D) report new data on the origins of intergalactic gas
   (E) reconcile opposing views on the formation of intergalactic gas

  2. The author uses the phrase “orthodox view of the universe” (line 3) to refer to the belief that
   (A) the space between the galaxies is devoid15 of matter
   (B) the space between galaxies is occupied by stars that cannot be detected by optical photographs
   (C) galaxies have decreased in mass by half since their formation
   (D) galaxies contain stars, each the size of Jupiter, which form clusters
   (E) galaxies are being penetrated16 by gas forced out of other galaxies by supernova explosions.

  3. It can be inferred from the passage that, if Fabian is correct, gas in the peripheral17 regions of a galaxy cluster
   (A) streams outward into intergalactic space
   (B) is hotter than gas in the central regions of the galaxy
   (C) is composed primarily of gas left over from the big bang
   (D) results in the creation of unusually large stars
   (E) expands to increase the size of the galaxy

  4. The author of the passage probably mentions Canizares‘ determination in order to
   (A) clarify an ambiguity18 in Fabian‘s research findings
   (B) illustrate a generalization19 about the temperature of gas in a galaxy cluster
   (C) introduce a new argument in support of the orthodox view of galaxies
   (D) provide support for Fabian‘s assertions about the Perseus galaxies
   (E) provide an alternate point of view concerning the movement of gas within a galaxy cluster

  5. According to the passage, Fabian believes that gas flowing into a central galaxy has which of the following characteristics?
   (A) It is one-tenth hotter than it was in the outer regions of the galaxy cluster.
   (B) It emits radiation with wavelengths that change as the gas moves toward the center of the galaxy.
   (C) The total amount of radiation emitted diminishes as the gas cools.
   (D) It loses 90 percent of its energy as it moves to the center of the galaxy.
   (E) It condenses at a rate much slower than the rate of decrease in temperature as the gas flows inward.

  6. According to the passage, Fabian‘s theory makes use of which of the following principles?
   (A) Gas emanating20 from an explosion will be hotter the more distant it is from the origin.
   (B) The wavelength12 of radiation emitted by a gas as it cools remains21 constant.
   (C) If pressure remains constant, the volume of a gas will decrease as it is cooled.
   (D) The volume of a gas will increase as the pressure increases.
   (E) As gas cools, its density22 decreases.

  7. It can be inferred from the passage that which of the following is true of Fabian‘s theory?
   (A) It did not receive approval until Canizares‘ work was published.
   (B) It was not widely accepted in the 1970‘s.
   (C) It did not receive support initially23 because technology was not available to confirm its tenets.
   (D) It supports earlier speculation that intergalactic gaswas largely the result of explosions outside thegalaxy.
   (E) It was widely challenged until x-ray evidence of gas temperatures in NGC 1275 had been presented.


1 astronomers 569155f16962e086bd7de77deceefcbd     
n.天文学者,天文学家( astronomer的名词复数 )
  • Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
  • Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪,为什么只有土星有光环。 来自《简明英汉词典》
2 galaxies fa8833b92b82bcb88ee3b3d7644caf77     
星系( galaxy的名词复数 ); 银河系; 一群(杰出或著名的人物)
  • Quasars are the highly energetic cores of distant galaxies. 类星体是遥远星系的极为活跃的核心体。
  • We still don't know how many galaxies there are in the universe. 我们还不知道宇宙中有多少个星系。
3 apparently tMmyQ     
  • An apparently blind alley leads suddenly into an open space.山穷水尽,豁然开朗。
  • He was apparently much surprised at the news.他对那个消息显然感到十分惊异。
4 galaxy OhoxB     
  • The earth is one of the planets in the Galaxy.地球是银河系中的星球之一。
  • The company has a galaxy of talent.该公司拥有一批优秀的人才。
5 physicist oNqx4     
  • He is a physicist of the first rank.他是一流的物理学家。
  • The successful physicist never puts on airs.这位卓有成就的物理学家从不摆架子。
6 drizzle Mrdxn     
  • The shower tailed off into a drizzle.阵雨越来越小,最后变成了毛毛雨。
  • Yesterday the radio forecast drizzle,and today it is indeed raining.昨天预报有小雨,今天果然下起来了。
7 constellation CptzI     
  • A constellation is a pattern of stars as seen from the earth. 一个星座只是从地球上看到的某些恒星的一种样子。
  • The Big Dipper is not by itself a constellation. 北斗七星本身不是一个星座。
8 strands d184598ceee8e1af7dbf43b53087d58b     
n.(线、绳、金属线、毛发等的)股( strand的名词复数 );缕;海洋、湖或河的)岸;(观点、计划、故事等的)部份v.使滞留,使搁浅( strand的第三人称单数 )
  • Twist a length of rope from strands of hemp. 用几股麻搓成了一段绳子。 来自《简明英汉词典》
  • She laced strands into a braid. 她把几股线编织成一根穗带。 来自《简明英汉词典》
9 speculation 9vGwe     
  • Her mind is occupied with speculation.她的头脑忙于思考。
  • There is widespread speculation that he is going to resign.人们普遍推测他要辞职。
10 noted 5n4zXc     
  • The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
  • Jim is noted for arriving late for work.吉姆上班迟到出了名。
11 wavelengths 55c7c1db2849f4af018e7824d42c3ff2     
n.波长( wavelength的名词复数 );具有相同的/不同的思路;合拍;不合拍
  • I find him difficult to talk to—we're on completely different wavelengths. 我没法和他谈话,因为我们俩完全不对路。 来自《简明英汉词典》
  • Sunlight consists of different wavelengths of radiation. 阳光由几种不同波长的射线组成。 来自辞典例句
12 wavelength 8gHwn     
  • The authorities were unable to jam this wavelength.当局无法干扰这一波长。
  • Radio One has broadcast on this wavelength for years.广播1台已经用这个波长广播多年了。
13 illustrate IaRxw     
  • The company's bank statements illustrate its success.这家公司的银行报表说明了它的成功。
  • This diagram will illustrate what I mean.这个图表可说明我的意思。
14 prospects fkVzpY     
  • There is a mood of pessimism in the company about future job prospects. 公司中有一种对工作前景悲观的情绪。
  • They are less sanguine about the company's long-term prospects. 他们对公司的远景不那么乐观。
15 devoid dZzzx     
  • He is completely devoid of humour.他十分缺乏幽默。
  • The house is totally devoid of furniture.这所房子里什么家具都没有。
16 penetrated 61c8e5905df30b8828694a7dc4c3a3e0     
adj. 击穿的,鞭辟入里的 动词penetrate的过去式和过去分词形式
  • The knife had penetrated his chest. 刀子刺入了他的胸膛。
  • They penetrated into territory where no man had ever gone before. 他们已进入先前没人去过的地区。
17 peripheral t3Oz5     
  • We dealt with the peripheral aspects of a cost reduction program.我们谈到了降低成本计划的一些外围问题。
  • The hotel provides the clerk the service and the peripheral traveling consultation.旅舍提供票务服务和周边旅游咨询。
18 ambiguity 9xWzT     
  • The telegram was misunderstood because of its ambiguity.由于电文意义不明确而造成了误解。
  • Her answer was above all ambiguity.她的回答毫不含糊。
19 generalization 6g4xv     
  • This sweeping generalization is the law of conservation of energy.这一透彻的概括就是能量守恒定律。
  • The evaluation of conduct involves some amount of generalization.对操行的评价会含有一些泛泛之论。
20 emanating be70e0c91e48568de32973cab34020e6     
v.从…处传出,传出( emanate的现在分词 );产生,表现,显示
  • Even so, there is a slight odour of potpourri emanating from Longfellow. 纵然如此,也还是可以闻到来自朗费罗的一种轻微的杂烩的味道。 来自辞典例句
  • Many surface waters, particularly those emanating from swampy areas, are often colored to the extent. 许多地表水,特别是由沼泽地区流出的地表水常常染上一定程度的颜色。 来自辞典例句
21 remains 1kMzTy     
  • He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
  • The remains of the meal were fed to the dog.残羹剩饭喂狗了。
22 density rOdzZ     
  • The population density of that country is 685 per square mile.那个国家的人口密度为每平方英里685人。
  • The region has a very high population density.该地区的人口密度很高。
23 initially 273xZ     
  • The ban was initially opposed by the US.这一禁令首先遭到美国的反对。
  • Feathers initially developed from insect scales.羽毛最初由昆虫的翅瓣演化而来。