Astronomy Picture of the Day——木星的光晕
The Ghost of Jupiter's Halo
Image Credit & Copyright: CHART32 Team
Explanation: Close-up images of NGC 3242 show the cast off shroud of a dying, sun-like star fancifully known as The Ghost of Jupiter nebula. But this deep and wide telescopic view also finds the seldom seen outer halo of the beautiful planetary nebula at the upper left, toward Milky Way stars and background galaxies in the serpentine constellation Hydra. Intense and otherwise invisible ultraviolet radiation from the nebula's central white dwarf star powers its illusive glow in visible light. In fact, planets of NGC 3242's evolved white dwarf star may have contributed to the nebula's symmetric features and shape. Activity beginning in the star's red giant phase, long before it produced a planetary nebula, is likely the cause of the fainter more extensive halo. About a light-year across NGC 3242 is some 4,500 light-years away. The tenuous clouds of glowing material at the right could well be interstellar gas, by chance close enough to the NGC 3242's white dwarf to be energized by its ultraviolet radiation.
木魂星云的光晕
NGC3242的特写影像呈现了一颗类似被太阳抛出外层气壳的濒死恒星，这个星云被奇异地称为木魂星云。然而，在这幅远眺蜿蜒长蛇座方向的以银河系广阔恒星为背景的望远镜深空影像中，位于左上方的美丽行星状星云呈现出罕见的外晕。由星云中心白矮星发出的强烈而不可见的紫外线辐射激发星云辐射出幻影般的可见光。实际上，NGC 3242所演化的白矮星周围的行星可能对该星云的对称形状和特征有所影响。早在行星状星云形成之前，这颗恒星的红巨星阶段就开始了活动，这很可能是造成更黯淡、更广阔外晕的原因。NGC 3242的大小约一光年，距离地球约4,500光年。影像右侧稀薄炽热的物质云很可能是星际气体，碰巧距离NGC 3242的白矮星足够近，从而能够被它的紫外线辐射所激发。
参考文献：
https://apod.nasa.gov/apod/image/1907/NGC3242haloChart32.jpg
近期文章：
Astronomy Picture of the Day——广袤的日冕