当伴星围绕着主星运转时，它交替地朝着地球或背离地球运转。
As a companion star orbits its primary, it alternately approaches and recedes from the Earth.
当这些亮而且质量大的恒星耗尽了氢燃料时，它们就开始从主星序上端脱离。
As these luminous and massive stars exhaust their hydrogen fuel, they begin to depart from the upper end of the main sequence.
当一个天体的轨道处在尘埃云内时，由于与周边物质的引力作用，它的轨道将逐渐收缩，以螺旋渐进的方式接近主星。
But when a body orbits inside a gaseous disk, its orbit shrinks and the body spirals gradually towards the planet as a result of the gravitational interaction of the body with the surrounding gas.
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