Over billions of years, the gas was compressed by gravity into galaxies, stars, plants and eventually, even humans.

在数十亿年的时间里，这些气体被引力压缩成星系、恒星、植物，最终甚至变成了人类。

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On the other hand, a comparatively warm body with a small surface gravity, like Earth's moon, is unable to hold even the heaviest gas and thus lacks an atmosphere.

另一方面，像地球的卫星这种相对温暖、表面引力较小的天体，它们连最重的气体也无法容纳，因此也没有大气层。

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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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Stars, such as our sun, are giant balls of gas held together by gravity.

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Normal matter, which is mostly gas, has pressure and that resists gravity.

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The first stars formed when clouds of gas bunched together due not only to the pull of their own gravity, but also that of dark matter.

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