首页
登录
职称英语
Leaving aside the question of how black holes generate the energy in
Leaving aside the question of how black holes generate the energy in
游客
2025-02-22
43
管理
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. [br] The passage suggests that scientists consider their understanding of gamma-bursts to be
选项
A、incomplete because they still have yet to establish a taxonomy of the various types of GHBs they have observed
B、adequate enough to redirect research toward other more perplexing aspects of black holes
C、unsurprising, given that scientists have long felt kinetic energy to play a role in the emergence of GHBs
D、disappointing because the mechanism by which GHBs become visible is still poorly understood
E、in need of confirmation through comparison with another astronomical phenomenon that involves electromagnetic bursts
答案
A
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3967333.html
相关试题推荐
Leavingasidethequestionofhowblackholesgeneratetheenergyin
Leavingasidethequestionofhowblackholesgeneratetheenergyin
Leavingasidethequestionofhowblackholesgeneratetheenergyin
ThoughonemayquestionthedegreetowhichtheCivilWarrepresents
ThoughonemayquestionthedegreetowhichtheCivilWarrepresents
ThoughonemayquestionthedegreetowhichtheCivilWarrepresents
QUIBBLES:OBJECTIONS::A、questions:repliesB、foibles:flawsC、estimations:
Directions:Eachofthefollowingreadingcomprehensionquestionsisbasedonth
Howisanewbornstarformed?Fortheanswertothisquestion,wemu
Howisanewbornstarformed?Fortheanswertothisquestion,wemu
随机试题
WhichofthefollowingsentencesexpressesUNWILLINGNESS?A、Hardasmyworkis,I
HowmanywatchesdidMr.Swift’scompanyordered?[br]Whatmadeseveralmostim
Coffeeisapowerfuldrink.Onapersonallevel,ithelpskeepusawakeanda
下列各项使用一字线连接号符合规范的是( )。A.永定河大致以西北—东南的走向流
轴心受力构件的强度计算一般采用轴力设计值N除以净截面面积An,这对( )是偏于
关于体外受精,下列表述正确的是A.体外受精现已发展到第三代试管婴儿,技术上更加完
患者男,70岁。确诊为阿尔茨海默病2年,近期出现分不清季节的问题,夏天当冬天,穿
右图所示的是哪种典型地貌?() A.风蚀地貌 B.冰川地貌 C.丹
在我国,保障人民当家作主的国家制度是()。A.中华人民共和国宪法 B.我国
根据《建设工程施工合同(示范文本)》通用合同条款,关于工程保修的说法,正确的是(
最新回复
(
0
)