M57：哈勃拍摄的环状星云
(原标题: M57: The Ring Nebula from Hubble)
2023-04-02
浏览次数: 26
几百年前，观星者发现了它，但他们无法理解它不同寻常的形状。它看起来像天空中的一个环。除了土星环，环状星云（M57）可能是最著名的天体环。我们现在知道它是什么，它的标志性形状是由于我们幸运的视角。最近对这个正在膨胀的星云的三维结构的绘制，部分是基于这张清晰的哈勃图像，表明这个星云是一个相对致密的，像甜甜圈一样的环，包裹在一个（美式）足球形状的发光气体云的中间。我们从地球上看到的是足球的长轴，正对着圆环。当然，在这个被充分研究的行星状星云的例子中，发光的物质并不是来自行星。相反，气体裹尸布代表了这颗垂死的、曾经像太阳一样的恒星所排出的外层，现在在星云中心可以看到一个微小的光点。来自炽热中央恒星的强烈紫外线使气体中的原子电离。环状星云直径约1光年，距离我们2500光年。
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It was noticed hundreds of years ago by stargazers who could not understand its unusual shape. It looked like a ring on the sky. Except for the rings of Saturn, the Ring Nebula (M57) may be the most famous celestial circle. We now know what it is, and that its iconic shape is due to our lucky perspective. The recent mapping of the expanding nebula's 3-D structure, based in part on this clear Hubble image,indicates that the nebula is a relatively dense, donut-like ring wrapped around the middle of an (American) football-shaped cloud of glowing gas. Our view from planet Earth looks down the long axis of the football, face-on to the ring. Of course, in this well-studied example of a planetary nebula, the glowing material does not come from planets. Instead, the gaseous shroud represents outer layers expelled from the dying, once sun-like star, now a tiny pinprick of light seen at the nebula's center. Intense ultraviolet light from the hot central star ionizes atoms in the gas. The Ring Nebula is about one light-year across and 2,500 light-years away.