首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
考研
Before there were black holes and stars and galaxies, the universe went through a period just after the big bang known as the Da
Before there were black holes and stars and galaxies, the universe went through a period just after the big bang known as the Da
admin
2015-02-12
106
问题
Before there were black holes and stars and galaxies, the universe went through a period just after the big bang known as the Dark Age of the Universe that lasted until evolving structure ultimately led to the first stars. Jordi Miralda-Escude, an astronomer at Ohio State University in Columbus, describes the Dark Age as the epoch when the universe had become completely dark as it gradually cooled following the big bang and "all the matter that forms us today was spread around space and uniformly distributed."
Little differences in the density of matter that had been present since the beginning of the universe gradually grew larger as a result of gravitational attraction. Eventually the density was large enough to cause a gravitational collapse and the first star was born. These first stars, according to Miralda-Escude, were likely quite massive and when they exploded as supernovae they littered the universe with atoms heavier than hydrogen and helium which were required for the formation of planets in the next generation of stars. "In the beginning, the universe contained only hydrogen and helium, but at the present time planets like the Earth are made of heavier atoms," he said. "They all come from stars. So all the atomic nuclei on which life is based—except for hydrogen—were made in stars."
One of the curiosities Miralda-Escude is trying to pin down is when the first star was born after the Dark Age began. "Imagine you are an observer floating in space and looking through the universe in the Dark Age and around you it is completely dark," he said. "The temperature is decreasing so the cosmic background light has all shifted to infrared wavelengths, and there is nothing in visual light. Then, all of a sudden you see the first star appear in the distance."
Miralda-Escude estimates that the first visible star probably appeared about 75 million years after the big bang. Today, the universe is nearly 14 billion years old and contains billions of galaxies, each one with billions of stars.
What caused the differences in the density of matter to grow larger?
选项
A、Gravitational attraction.
B、Little differences in the density of matter.
C、The big bang.
D、Massive stars.
答案
A
解析
属事实细节题。第二段首句告诉我们,由于引力,物质密度的差别逐渐增大。
转载请注明原文地址:https://kaotiyun.com/show/2E74777K
0
考研英语一
相关试题推荐
TheGeneVariationCausesanAutismCommongeneticvariationsthatcancontributetoautismhavebeenreliablyidentifiedfo
CharacteristicMedicalTreatmentItisstartlinghowcommonthesechronicdiseaseslikecancerarewhenonelooksatthenum
Attemptstounderstandtherelationshipbetweensocialbehaviorandhealthhavetheirorigininhistory.Dubos(1969)suggested
Attemptstounderstandtherelationshipbetweensocialbehaviorandhealthhavetheirorigininhistory.Dubos(1969)suggested
Attemptstounderstandtherelationshipbetweensocialbehaviorandhealthhavetheirorigininhistory.Dubos(1969)suggested
Throughoutthe19thcenturyandintothe20th,citizensoftheUnitedStatesmaintainedabiasagainstbigcities.Mostlivedon
Throughoutthe19thcenturyandintothe20th,citizensoftheUnitedStatesmaintainedabiasagainstbigcities.Mostlivedon
Throughoutthe19thcenturyandintothe20th,citizensoftheUnitedStatesmaintainedabiasagainstbigcities.Mostlivedon
Itisonlyinrecentyearsthatwehaverecognizedthat_____.Fromparagraph1wecaninferthatitisnowpossibleforwomen
Untilrecently,mostpopulationgrowthhasoccurredinrelativelydenseurbanenvironments.In【C1】______words,evenifwewerew
随机试题
铣削矩形牙嵌离合器时,若采用将离合器各齿侧均铣得偏离中心一个距离e获得齿侧间隙方法,离合器在啮合时,齿侧面将___________。
下列关于进动的叙述,错误的是
A.1年B.2年C.3年D.4年E.5年定点零售药店外配处方的保存年限是
低渗性脱水时,体液的容量改变为
银行对工程设计方案进行分析和评估,就是要分析工程设计方案是否经济合理,是否符合项目的总体发展。对工程设计方案的分析评估可以从()方面进行分析。
选择书心用纸,一般做法是()。
某刑事人类学家在对260名杀人犯的外貌进行了考察后,发现他们具有一些共同的生理特征,于是得出“杀人犯具有广颚、颧骨凸出、头发黑而短特征”的结论。以下哪项与上述推理方式相同?
文中画线处“红移”的意思是______。“微波背景辐射是大爆炸阶段的直接遗迹”,以下不能作为其推断依据的一项是______。
设(I)和(Ⅱ)都是4元齐次线性方程组,已知ξ1=(1,0,1,1)T,ξ2=(一1,0,1.0)T,ξ3=(0,l,1,0)。是(I)的一个基础解系,η1=(0,1,0,1)T,η=(1,1一1,0)T是(Ⅱ)的一个基础解系.求(I)和(Ⅱ)公共解.
DarkForcesDominateUniverseTheEarth,moon,sunandallvisiblestarsintheskymakeuplessthanonepercentoftheuni
最新回复
(
0
)