“聚集体”用英语怎么说？

聚集体结构紧密并且形状接近于球形.Aggregates are compact and close to spherical in shape.这些多聚集体只有在非常窄的温度和pH范围内方是稳定的.Such polyaggregates are stable only over very narrow temperature and pH regions.这说明星云是恒星的聚集体.This suggest that the nebula...