In those cases, the star isn't big enough to keep the disk in check, so the disk starts to collapse under its own gravity and forms planets.
在那些情况中，恒星并没有达到控制磁盘的地步，因此磁盘在它自己的重力下开始瓦解并形成行星。
2
Swing-type check off er the least pressure drop and offer simple automatic closure; when fluid flow stops gravity and flow reversal closes valve.
旋启式止回阀压降最小，能够完全自动关闭，即在介质流动停止、重力和介质倒流的状态下自动关闭阀门。
3
Gravity ball check valves are converted to vent valves by replacing the standard ball with a floater ball and inverting the valve at installation-with seat up.