In comparison to their size on the main sequence, the stars now become giants. 同它在主星序上的大小相比,恆星現在就成了巨星。
When a massive proto -star approaches the main sequence, its surface temperature is low and it can not ionize the ambient gas. 當一個大質量原星接近主星序時,它的表面溫度是低的,因而不能電離周圍的氣體。