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    SAT官方每日一题附答案和解析[阅读](2019年3月4日)

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    Critical Reading>Select an Answer

    Light from distant quasars -- early galaxies that shine with tremendous brightness -- has given researchers a new clue to the origin of vast magnetic fields studding today's galaxies: They were running strong when the universe was only a third of its present age.

    Astronomers had observed that radio emissions from quasars tend to be angled, or polarized, in such a way that powerful magnetic fields must have twisted them. The greater their distance from Earth, the more polarized their light. But researchers didn't know whether the magnetic fields were part of the quasar or were present in galaxies encountered by quasar light as it made its journey to our telescopes.

    So a team led by astronomers from the Swiss Federal Institute of Technology (ETH Zurich) scanned more than 70 of those quasars using the European Southern Observatory's Very Large Telescope in Chile to look for signs of galaxies hiding in front of the quasars. Specifically, they checked for a feature called the magnesium(II) absorption line, a reduction in the intensity of light of a certain wavelength, which is a commonly used indicator that gas from a star-forming galaxy has soaked up that light.

    The researchers report that light from quasars showing the magnesium(II) line was more strongly polarized than light from other quasars in the sample. The interpretation: that light did indeed pass through regular galaxies and that it likely acquired its polarization in the process.

    They estimated the age of the magnetic galaxies by measuring the red shift of the absorption line -- the observed reddening of light that occurs when galaxies move rapidly apart. The typical red shift of the inferred galaxies corresponded to an age of 5.2 billion years, study author Francesco Miniati says. Precision measurements of the cosmic microwave background peg today's universe at 13.7 billion years old.

    According to the passage, the astronomers wanted to determine if light emitted by distant quasars was affected by _______
    A.the number of stars in those quasars.
    B.those quasars' proximity to galaxies.
    C.the age of those quasars.
    D.those quasars' distances from Earth.

    重点单词   查看全部解释    
    critical ['kritikəl]

    想一想再看

    adj. 批评的,决定性的,危险的,挑剔的
    a

     
    galaxy ['gæləksi]

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    n. 银河,一群显赫之人

    联想记忆
    cosmic ['kɔzmik]

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    adj. 宇宙的,广大无边的,无限的

    联想记忆
    wavelength ['weiv.leŋθ]

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    n. 波长,波段

    联想记忆
    twisted ['twistid]

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    adj. 扭曲的 v. 扭动(twist的过去式)

     
    proximity [prɔk'simiti]

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    n. 接近,亲近

     
    affected [ə'fektid]

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    adj. 受影响的,受感动的,受疾病侵袭的 adj. 做

    联想记忆
    observatory [əb'zə:və.tri]

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    n. 天文台,气象台,了望台

    联想记忆
    indicator ['indikeitə]

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    n. 指示器,指示剂
    [计算机] 指示符

     
    universe ['ju:nivə:s]

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    n. 宇宙,万物,世界

    联想记忆
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