2025年3月7日
Planetary Nebula Abell 7
Image Credit & Copyright: Vikas Chander
Explanation: Very faint planetary nebula Abell 7 is about 1,800 light-years distant. It lies just south of Orion in planet Earth’s skies toward the constellation Lepus, The Hare. Surrounded by Milky Way stars and near the line-of-sight to distant background galaxies its generally simple spherical shape, about 8 light-years in diameter, is revealed in this deep telescopic image. Within the cosmic cloud are beautiful and complex structures though, enhanced by the use of long exposures and narrowband filters that capture emission from hydrogen, sulfur, and oxygen atoms. Otherwise Abell 7 would be much too faint to be appreciated by eye. A planetary nebula represents a very brief final phase in stellar evolution that our own Sun will experience 5 billion years hence, as the nebula’s central, once sun-like star shrugs off its outer layers. Abell 7 itself is estimated to be 20,000 years old. But its central star, seen here as a fading white dwarf, is some 10 billion years old.
Tomorrow’s picture: light-weekend
行星状星云Abell 7
影像提供与版权: Vikas Chander
说明: 在地球天空中，极为昏暗的行星状星云Abell 7，位于猎户座之南的天兔座方向，离我们约有1,800光年远。周围环拱着许多银河恒星的这团星云，视线上也与许多背景星系重叠，而在这幅深空望远镜影像里，这团极昏暗肉眼不得见、直径约8光年、形状近乎球形的的星云清楚可辨。此外，它内部美丽但较复的结构，也因透过长曝光成像及窄波段滤镜记录氢、硫和氧原子的辐射，而得以突显出来。行星状星云是恒星演化过程中，极为短暂演化终点阶段的代表性天体。在这个范例里，此星云是其中心那颗前身为类太阳恒星所抛出的外层气壳，而我们的太阳在50亿年之后，也会经历此一阶段。Abell 7的年龄估计约有20,000年，星云中心那颗逐渐暗去的白矮星，其年龄则在100亿年左右。
明日的图片: light-weekend
