passage 66 到达地球的宇宙射线的来源
★★★
文章分析：
①Supernovas in the Milks Ways are the likeliest source for most of the cosmic rays reaching Earth. ②However, calculations show that supernovas cannot produce ultrahigh-energy cosmic rays (UHECRs), which have energies exceeding 1018 electron volts. ③It would seem sensible to seek the source of these in the universe’s most conspicuous energy factories: quasars and gamma-ray bursts billions of light-years away from Earth. ④But UHECRs tend to collide with photons of the cosmic microwave background—pervasive radiation that is relic of the early universe. ⑤The odds favor a collision every 20 million light-years, each collision costing 20 percent of the cosmic ray’s energy. ⑥Consequently, no cosmic ray traveling much beyond 100 million light-years can retain the energy observed in UHCERs.
①观点v1，超新星可能是宇宙射线的来源
②转折事实，但它能量不够
③顺承观点v2，那就得去寻找那些亿万光年之外的能量来源
④转折事实，但是这些射线是会和宇宙微波背景中的光子碰撞的
⑤顺承事实，而且每两百万年碰撞一次，一次丢失20%的能量
⑥顺承观点， ×v2，因此超过一亿光年就不是我们的目标了。
For the following question,consider each of the choices separately and select all that apply.
1. It can be inferred that the author of the passage would agree with which of the follow about the origin of UHECRs that reach Earth?
ABC
A. The origin is something other than supernovas in the Milky Way.
B. The origin is most likely something other than very distant quasars or gamma-ray bursts.
C. The origin is most likely no more than a little over 100 million light-years away from Earth.小于等于，不能超过一亿光年太多。就不讲人话体质。
2. In the context of the author’s argument, the last sentence performs which of the following functions?
C
A. It explains a criterion that wasemployed earlier in the argument. 无关
B. It shows that an apparently plausible position is actually self-contradictory. 没有证据
C. It is a conclusion drawn in the course of refuting a potential explanation.
D. It overturns an assumption onwhich an opposing position depends. 没有证据
E. It states the main conclusionthat the author is seeking to establish. 作者并未明确表达观点。不是作者要建立的结论，而是要反驳一种解释。
补充同学对于B中self-contradictory的疑惑：
self-contradictory是自己给证据，但是观点又不符合。问题是后面相反的证据是作者给的，这篇文章就是提供论证说明“寻找亿万年之外的来源”这个观点本身不靠谱，不是在说原来观点的达成过程有问题。
背景拓展：
Supernova 超新星，这个名词是沃尔特·巴德和弗里茨·兹威基在1931年提出的：
A supernova is a powerful and luminous stellar explosion.
超新星是某些恒星在演化接近末期时经历的一种剧烈爆炸。这种爆炸都极其明亮，过程中所突发的电磁辐射经常能够照亮其所在的整个星系，并可能持续几周至几个月才会逐渐衰减。而在此期间，一颗超新星所释放的辐射能量可以与太阳在其一生中辐射能量的总和相当。恒星通过爆炸可以将其大部分甚至几乎所有物质以高至十分之一光速的速度向外抛散，并向周围的星际物质辐射激波。这种激波会导致一个由膨胀的气体和尘埃构成的壳状结构形成，这被称作超新星遗迹。超新星是星系引力波潜在的强大来源。初级宇宙射线中来自超新星的占了很大的比例。
cosmic rays 宇宙射线
宇宙射线，是来自外太空的带电高能次原子粒子。
1912年，德国科学家韦克多·汉斯带着电离室在乘气球升空测定空气电离度的实验中，发现电离室内的电流随海拔升高而变大，从而认定电流是来自地球以外的一种穿透性极强的射线所产生的，于是有人为之取名为“宇宙射线”。
宇宙线大致可以分成两类：原生和衍生宇宙线。来自太阳系外的天文物理产生的宇宙线是原宇宙线；这些原宇宙线会和星际物质作用产生衍生（二次）宇宙线穿透地球的大气层和表面。
主要的初级宇宙射线（来自深太空与大气层撞击的粒子）成分在地球上一般都是稳定的粒子，像是质子、原子核、或电子。但是，有非常少的比例是稳定的反物质粒子，像是正电子或反质子，这剩余的小部分是研究的活跃领域。
大约89%的宇宙线是单纯的质子，10%是氦原子核（即α粒子），还有1%是重元素。这些原子核构成宇宙线的99%。孤独的电子（像是β粒子，虽然来源仍不清楚），构成其余1%的绝大部分；γ射线和超高能中微子只占极小的一部分。
quasars and gamma-ray bursts 类星体和伽马射线爆发
A quasar (/ˈkweɪzɑːr/) (also known as a quasi-stellar object abbreviated QSO) is an extremely luminous active galactic nucleus (AGN), in which a supermassive black hole with mass ranging from millions to billions of times the mass of the Sun is surrounded by a gaseous accretion disk. As gas in the disk falls towards the black hole, energy is released in the form of electromagnetic radiation, which can be observed across the electromagnetic spectrum. The power radiated by quasars is enormous: the most powerful quasars have luminosities thousands of times greater than a galaxy such as the Milky Way.
In gamma-ray astronomy, gamma-ray bursts (GRBs) are extremely energetic explosions that have been observed in distant galaxies. They are the brightest electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several hours.
cosmic microwave background 宇宙微波背景
微波背景辐射是宇宙中“最古老的光”，就是大爆炸的遗迹，穿越了漫长的时间与空间后成为了微波，充盈在整个宇宙空间里。需要注意不要把“大爆炸”理解为一般意义上的爆炸，比如从一个点炸裂开来四散辐射，因为大爆炸并不是在某个空间中的一点发生的，是大爆炸创造了空间本身。在宇宙中，微波背景辐射是均匀的，来自各个方向都一样，因此好比宇宙的“背景”。是来自宇宙空间背景上的各向同性的微波辐射，也称为宇宙背景辐射。
The image reveals 13.77 billion year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies. The signal from our galaxy was subtracted using the multi-frequency data.
The cosmic microwave background (CMB, CMBR), in Big Bang cosmology, is electromagnetic radiation as a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all space. It is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe, dating to the epoch of recombination.
With a traditional optical telescope, the space between stars and galaxies (the background) is completely dark. However, a sufficiently sensitive radio telescope shows a faint background noise, or glow, almost isotropic, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1964 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s, and earned the discoverers the 1978 Nobel Prize in Physics.
