How big they get depends on their distance from the star and the density and composition of the protoplanetary nebula.
他们的形体能达到多大取决于他们离恒星的距离和原行星星云的组成。
A Hubble Space Telescope image shows "proplyds, " or protoplanetary disks, in the Orion Nebula.
这是哈勃望远镜拍摄到的猎户星云中的原行星盘(proplyds，protoplanetary disks)。
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