Most astronomers believe that the large concentration of mass at the galaxy's center is a black hole whose gravity is causing the gas to whirl.

大多数天文学家认为，星系中心的大量物质是一个黑洞，它的引力导致气体旋转。

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A black hole is a concentration of mass great enough that the force of gravity prevents anything from escaping from it except through quantum tunneling behavior.

一个黑洞是物质浓缩到足够大的以致引力除了通过量子隧道行为之外阻止任何东西从它那里逃逸。

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Study on relationship between extinction coefficient and mass concentration.

气溶胶消光系数与质量浓度的相关性研究。

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We currently don't have a good term for EVs' distinctive concentration of mass, with batteries slung low as possible and centroid to the vehicle.

WSJ: 2012 Tesla Model S Signature Performance Review: I Am Silent, Hear Me Roar | Rumble Seat by Dan Neil

No one has ever forcibly moved that many people without concentration camps and mass death through plague.

FORBES: The Republican Party Needs A Reset On Immigration

And in present day Namibia, frequented as it is by hundreds of thousands of tourists - German and other kinds - there is no standing memorial to the Namibian dead, no plaque at Luderitz, Swakopmund or Shark Island to mark the sites of German concentration camps or the mass graves of those who died.

BBC: African viewpoint: Remembering German crimes in Namibia