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  1. ... as the mass of the black hole increases, so while an earth- mass black hole would have a density of 2 1030 kg/m3, a supermassive black hole of 109 solar masses ...

    分類:科學 > 其他:科學 2007年06月26日

  2. ... based on a Cs atom unperturbed by black -body radiation, and that the frequencies of primary frequency... that: "The kilogram is the unit of mass ; it is equal to the mass of the international prototype of...

    分類:科學 > 其他:科學 2006年01月29日