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
About 2,500 of so-called supernovae are known inside our galaxy and beyond. But exactly what they were before they exploded is n
About 2,500 of so-called supernovae are known inside our galaxy and beyond. But exactly what they were before they exploded is n
admin
2015-04-10
52
问题
About 2,500 of so-called supernovae are known inside our galaxy and beyond. But exactly what they were before they exploded is not so clear. The hunt for supernovae, from their origins to their long-term effects, is heating up rapidly. Understanding these incendiary objects is important in part because they are responsible for creating most of the elements in the universe, including the stuff of which people, plants and planets are made. A supernova is relatively easy to detect because of the intense radiation it casts off in visible light and other wavelengths. Figuring out what the star looked like prior to the explosion, however, requires probing into the archives of astronomy.
A separate team of supernova hunters did just that, using a decade of Hubble Space Telescope images to search for possible pre-supernova stars. Their new findings support existing theory of supernova mechanics, which holds that only very massive stars explode. When a massive star burns up all its hydrogen fuel, it casts its outer layers into space and then collapses into a dense neutron star or black hole. Theorists believe that stars must be about 10 to 20 times the mass of the sun to support such an explosive scenario. Such heavy objects have brief lives, typically less than 20 million years, compared with the sun, which is middle-aged and already 4. 6 billion years old.
Ground-based telescopes that observed the actual supernova explosions are not as accurate as Hubble, however, due to air turbulence, so scientists require follow-up Hubble observations to see if they are in the right positions. One has already been eliminated, Alexei Filippenko of the University of California at Berkeley said, but he’s confident at least a couple of the remaining five will prove to be actual precursor stars. Astronomers have known for decades that the universe is expanding. But in the late 1990s they began to realize that the expansion is occurring at an ever-faster rate. This suggests that some mysterious, unseen force is at work across great distances, breaking the will of gravity that would otherwise rein in the universe eventually.
Supernovae are useful in this research because they can be seen from far away. Astronomers measure how much an exploded star’s light has stretched, which tells them the speed at which the object is receding. By comparing this to nearby supernovae, researchers can refine the universal expansion’s rate of acceleration. In particular, the orbiting observatory’s keen new eyesight can be used to analyze pinpricks of light from very distant objects and learn what they are and what they’re made of. This so-called spectroscopy technique is just like using a prism to break white light into its constituent colors.
The research of what supernovae were before they exploded can help researchers
选项
A、refine the universal expansion’s rate of acceleration.
B、measure how much an exploded star’s light has stretched.
C、analyze light from very distant objects.
D、find how the universe expands.
答案
A
解析
研究超新星爆炸之前的状况能帮助研究人员[A]更精确地计算宇宙膨胀的加速率。[B]测量一颗爆炸星星的光的延伸距离。[C]分析来自遥远星体的光。[D]发现宇宙是如何膨胀的。文章最后一段指出,超新星在这项研究中的作用很大。天文学家们对一颗爆炸星星的光的延伸距离进行测量,这能告诉他们这个星体的衰减速度。将这与附近的超新星相比较,研究人员可以对宇宙膨胀的加速率进行更加精确的计算。这说明超新星的最终作用是使研究人员对宇宙膨胀的加速率的了解更加精确。[B]不正确,因为“测量一颗爆炸星星的光的延伸距离”是天文学家们正在进行的研究;[C]是轨道天文台的作用,不是超新星的作用;[D]文中没有提及。
转载请注明原文地址:https://kaotiyun.com/show/iW74777K
0
考研英语一
相关试题推荐
Inthefollowingtext,somesentenceshavebeenremoved.ForQuestions41-45,choosethemostsuitableonefromthelist(A、B、C、
Concreteisprobablyusedmorewidelythananyothersubstanceexceptwater,yetitremainslargelyunappreciated."Somepeople
Therehasarisenduringthistwentiethcentury(asitarosebefore,inageswhichweliketocalldark)apronouncedantiintell
Therehasarisenduringthistwentiethcentury(asitarosebefore,inageswhichweliketocalldark)apronouncedantiintell
Spain’sgovernmentisnowchampioningacausecalled"righttobeforgotten".IthasorderedGoogletostopindexinginformation
NetworkSafetyAHousecommitteeisreopeningitsinvestigationofInternetservicesthatletcomputerusersdistributemusi
Itisnotunusualforchiefexecutivestocollectmillionsofdollarsayearinpay,stockoptions,andbonuses.Inthelastfif
A.BenefitingfromanearliermodelB.ImportantoperativeconditionsC.ExaminingthepublicconfusionD.Howit’salllinkedu
Therewasgreatpublicinterestwhenabigholemysteriouslyappearedinthemiddleofafield.Armymechanicsandengineerswer
Ifsabravemanwhoclaims"geniusinsciencehasbecomeextinct".Butthat’sexactlywhatpsychologistDeanKeithSimontondecl
随机试题
背景某企业新建厂区办公楼,建筑面积42605m2,为15层框架结构,裙房3层,外墙及隔墙由混凝土空心砌块砌筑。现结构及砌筑均已施工完毕,外墙抹灰已完,按经监理审核通过的施工方案拆除外脚手架,然后用吊篮进行外墙饰面防水涂料涂刷。脚手架拆除作业:本建筑平
利用计算机及计算机网络进行教学,使得学生和教师可以异地完成教学活动的一种教学模式称为____________。
静脉滴注抗生素,下列措施正确的是
雌激素与孕激素作用的相同点是
假设某工程中上部结构传至承台顶面处相应于荷载的标准组合下的竖向力Fk=10000kN、弯矩Mk=500kN.m、水平力Hk=100kN,设计承台尺寸为1.6m×2.6m,厚度为1.0m,承台及其上土平均重度为20kN/m3,桩数为5根。如图2.4—1l所示
下列费用项目中,属于综合单价的组成内容的有()。
下列各项中,应计入财务费用的有()。
按照现代管理学的定义,银行组织架构是由()所组成的一个系统。
张强:当一个地区的经济不景气时,许多人失业,于是他们降低生活消费,结果造成更多人失业,并导致经济恶化。经济不断恶化,最后物价降至最低点。低物价刺激人们增加生活消费,消费增加又导致经济状况改善。李明:如果人们失业的话,他们就无法增加消费,也没有钱购买生活必需
社会形态更替的客观必然性,主要是指社会形态依次更替过程和规律是客观的,其发展趋势是确定不移的。但是规律的客观性并不否定人们历史活动的能动性,并不排斥人们在遵循社会发展规律的基础上,对于某种社会形态的历史选择性。人们的历史选择性包含的意思有()
最新回复
(
0
)