题目内容
According to the passage, the fireball which emits the initial GRBs differs from the stage
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The author would regard the notion that certain proteins are essential to the survival of
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？
Just then he ______that the hen ______three eggs a day.
According to the passage, Leonard asserts that women's activities during the Civil War had
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