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GRE阅读高频机经原文:Supernovae Obscurat by dust

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  30. Supernovae & Obscuration by dust
  Recently, significant progress has been made by using Type Ia supernovae as ``standardizable candles''. Supernovae are rare - perhaps a few per century in a Milky-Way-sized galaxy - but modern telescopes allow observers to probe very deeply into small regions of the sky, covering a very large number of galaxies in a single observing run. Supernovae are also bright, and Type Ia's in particular all seem to be of nearly uniform intrinsic luminosity (absolute magnitude , typically comparable to the brightness of the entire host galaxy in which they appear)They can therefore be detected at high redshifts , allowing in principle a good handle on cosmological effects .
  Obscuration by dust is the leading concern about the reliability of the supernova results. Ordinary astrophysical dust does not obscure equally at all wavelengths, but scatters blue light preferentially, leading to the well-known phenomenon of ``reddening''. Spectral measurements by the two supernova teams reveal a negligible amount of reddening, implying that any hypothetical dust must be a novel ``grey'' variety. This possibility has been investigated by a number of authors . These studies have found that even grey dust is highly constrained by observations: first, it is likely to be intergalactic rather than within galaxies, or it would lead to additional dispersion in the magnitudes of the supernovae; and second, intergalactic dust would absorb ultraviolet/optical radiation and re-emit it at far infrared wavelengths, leading to stringent constraints from observations of the cosmological far-infrared background. Thus, while the possibility of obscuration has not been entirely eliminated, it requires a novel kind of dust which is already highly constrained (and may be convincingly ruled out by further observations).

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negligible ['neglidʒəbl]

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adj. 可以忽略的,微不足道的

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hypothetical ['haipəu'θetikəl]

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adj. 假设的,假定的,爱猜想的

 
variety [və'raiəti]

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n. 多样,种类,杂耍

 
obscure [əb'skjuə]

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adj. 微暗的,难解的,不著名的,[语音学]轻音的

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absorb [əb'sɔ:b]

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vt. 吸纳,吸引 ... 的注意,吞并

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galaxy ['gæləksi]

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n. 银河,一群显赫之人

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supernova [,sju:pə'nəuvə]

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n. [天]超新星

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additional [ə'diʃənl]

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adj. 附加的,另外的

 
probe [prəub]

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n. 探针,探测器,调查,查究
v. 用探针测

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covering ['kʌvəriŋ]

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n. 覆盖物,遮避物 adj. 掩护的,掩盖的

 

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