行星状星云Abell 7

2022年5月21日

Planetary Nebula Abell 7
Image Credit & Copyright: Donald Waid, Ron Dilulio

Explanation: Very faint planetary nebula Abell 7 is some 1,800 light-years distant, just south of Orion in planet Earth’s skies in 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 outlined in this deep telescopic image. Within its confines are beautiful, more complex details enhanced by the use of narrowband filters. Emission from hydrogen is shown in reddish hues with oxygen emission mapped to green and blue colors, giving Abell 7 a natural appearance that would otherwise 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. Its central star is seen here as a fading white dwarf some 10 billion years old.

Tomorrow’s picture: Tsunami on the Sun

行星状星云Abell 7
影像提供与版权: Donald Waid, Ron Dilulio

说明: 在地球天空中，极为昏暗的行星状星云Abell 7位在猎户座之南的天兔座内，离我们约有1,800光年远。这团周围环拱着许多银河系恒星的星云，视线上恰好与许多背景星系重叠，然而在这幅深空望远镜影像里，其直径约8光年、形状近乎球形的外观清楚可辨。此外，它内部美丽但较复的结构，也因透过窄波段滤镜成像而得以突显出来。在这幅自然色泽的Abell 7影像里，来自氢和氮的辐射上色为红色，而氧的辐射则以蓝-绿色来呈现，让这团极昏暗肉眼不得见的星云能为我们所观赏。在恒星演化过程中，行星状星云是极为短暂演化终点阶段的代表性天体，在此范例里，也是星云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50亿年之后也将经历此一阶段。据估计，Abell 7的年龄约为20,000年，而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: Tsunami on the Sun