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
外语
Leaving aside the question of how black holes generate the energy in gamma-ray bursts-cosmic explosions called GRBs-their
Leaving aside the question of how black holes generate the energy in gamma-ray bursts-cosmic explosions called GRBs-their
admin
2011-01-17
66
问题
Leaving aside the question of how black holes generate the energy in
gamma-ray bursts-cosmic explosions called GRBs-their sheer brilliance has
posed a dilemma. So much radiation emanates from the GRB’s compact space
Line that astronomers would like to conclude that the photons are too densely packed
(5) to allow each other to escape, but in that event, how can GRBs be observed?
The resolution of this conundrum, developed over the past several years, is
that the gammas are not emitted immediately; instead the initial energy release
of the explosion is stored in the kinetic energy of a shell of particles (including
photons as well as electrons and their antimatter counterpart, positrons). This
(10) produces a fireball moving at a speed close to that of light and expanding to a
diameter of 10 billion to 100 billion kilometers, then converting some of its
kinetic energy into electromagnetic radiation, yielding a GRB.
The initial gamma-ray emission is most likely the result of internal shock
waves within the expanding fireball, shocks which arise when faster blobs in the
(15) expanding material overtake slower blobs. Because the fireball is expanding so
close to the speed of light, the principles of relativity dictate that the timescale
witnessed by an external observer is vastly compressed, such that over a few
seconds the observer may witnesses a burst of gamma rays that required a day to
produce. The fireball continues to expand, eventually encountering and
(20) sweeping up surrounding gas, then subsequently generates another shock wave
at the boundary between the fireball and the external medium that persists as
the fireball slows down and shrinks. This external shock nicely accounts for the
GRB afterglow emission and the gradual degradation of this emission from
gamma rays to x-rays to visible light, then, finally, to radio waves.
(25) Although the fireball can transform the explosive energy into the observed
radiation, astronomers have yet to agree on what generates the energy to begin
with. One family of models, referred to as hypernovae, involves stars born with
masses greater than about 20 to 30 times that of our sun; simulations show that
the central core of such a star eventually collapses to form a rapidly rotating
(30) black hole encircled by a disk of leftover material. Nevertheless, compact-star
coalescence could still have a place in the big picture and a mechanism may
account for the poorly understood short-duration GRBs. Moreover, additional
models for GRBs are still in the running, one of which credits the birth of the
fireball to the extraction of energy from an electrically charged black hole. This
(35) model suggests that both the immediate and the afterglow emissions are
consequences of the fireball sweeping up the external medium. Astronomers
have come a long way in understanding gamma-ray bursts, but they still do not
know precisely what causes these explosions, and they know little about the
rich variety and subclasses of bursts.
Which of the following best expresses the main idea of the passage?
选项
A、Though the forces which influence GRBs are now established, scientists have yet to establish their cause.
B、Scientists have now established the role that kinetic energy plays in the existence of GRBs.
C、Certain aspects of GRBs have finally allowed scientists to link them to specific kinds of collapsed stars.
D、Though still perplexed by the cause of GRBs, scientists have discovered how they manage to escape the gravity of black holes.
E、Fireballs can transform explosive energy into observed radiation, as had long been hypothesized.
答案
D
解析
转载请注明原文地址:https://kaotiyun.com/show/DDjO777K
本试题收录于:
GRE VERBAL题库GRE分类
0
GRE VERBAL
GRE
相关试题推荐
InevertrustedhimbecauseIalwaysthoughtofhimassucha______character.
WhenJackDavis,9,looksupatthenightsky,hedoesn’tseejustthestars.Heseeshisfuture.ThefourthgradefromNewJer
Thereisnodoubtthatadults,andevenhighlyeducatedadults,varygreatlyinthespeedandefficiencyoftheirreading.Some
Theinterviewershouldtakedownnotesatthemomenttheperson______answerthequestions.
CarsareanimportantpartoflifeintheUnitedStates.Withoutacar,mostpeoplefeelthattheyare【C1】________Andevenifa
Thepassageisprimarilyconcernedwithdiscussing______WhichofthefollowingmostaccuratelystateafindingofBolte’srese
PAINTER:CARICATURIST::
ANECDOTE:AMUSEMENT::
SUBSTANTIATION:
Inmathematics,judgmentsaboutthevalidityofproofsaremediatedbypeer-reviewedjournals,toensure______,reviewersarec
随机试题
注册公开募集基金,由拟任基金管理人向中国证监会提交的文件不包括()。
利血平硝苯地平
如果不履行或不认真履行代理职责而给被代理人造成损害的,( )承担赔偿责任。
境外注册的会计师事务所申请银行证券保险业务临时许可证,应当具备下列条件()
下列关于时点指标的特点,描述错误的是()。
女,22岁。发现右下腹包块3个月,手术发现右卵巢被破坏,被一个囊性肿物所取代囊内充满脂性物质、毛发,囊壁可见牙齿。应诊断为
Inthefollowingtext,somesentenceshavebeenremoved.ForQuestions41-45,choosethemostsuitableonefromthelist(A、B、C、
在系统验收测试中,(17)是在一个模拟的环境下使用模拟数据运行系统;(18)是在一个实际环境中使用真实数据运行系统。
Cisco3548交换机采用telnet远程管理方式进行配置,其设备管理地址是222.38.12.23/24,缺省路由是222.38.12.1。下列对交换机预先进行的配置,正确的是()。
Mary______inthegardenwhenitbegantorain.
最新回复
(
0
)