Helix Nebula

这张螺旋星云的图像由NASA的银河演化的探测器拍摄的紫外图像和NASA的斯皮策空间望远镜拍摄的红外图像合成。图片版权：Galex，NASA/JPL-Caltech

The Helix nebula lies 650 light-years away in the constellation of Aquarius. Also known by the catalog number NGC 7293, it is a typical example of a class of objects called planetary nebulae. Discovered in the 18th century, these cosmic works of art were erroneously named for their resemblance to gas-giant planets.

螺旋星云位于天琴座，距离地球650光年。它也被称为NGC 7293，是一类被称为行星星云的典型例子。这些宇宙艺术品于18世纪被发现，其名称是由于它们与气态巨行星相似而误用的。

A white dwarf has been detected at the center of the nebula. The white dwarf is presumed to be about the size of Earth, but has a mass very close to that of the original star. From the NASA description: "The glow from planetary nebulae is particularly intriguing as it appears surprisingly similar across a broad swath of the spectrum, from ultraviolet to infrared. The Helix remains recognizable at any of these wavelengths, but the combination shown here highlights some subtle differences. The intense ultraviolet radiation from the white dwarf heats up the expelled layers of gas, which shine brightly in the infrared. GALEX has picked out the ultraviolet light pouring out of this system, shown throughout the nebula in blue, while Spitzer has snagged the detailed infrared signature of the dust and gas in yellow."

一个白矮星已被探测到位于星云中心。该白矮星的尺寸被认为与地球相当，但其质量接近原始恒星的质量。根据NASA的描述：'行星状星云的光芒尤其引人注目，因为它在从紫外到红外的广阔光谱范围内看起来出奇地相似。螺旋星云在任何这些波长下都能被识别，但此处展示的组合突显了一些细微差异。来自白矮星的强烈紫外辐射加热了被抛射的气体层，这些气体在红外波段发出明亮的光芒。GALEX捕捉到了这个系统中喷涌而出的紫外光，以蓝色显示在整个星云中，而斯皮策望远镜则捕捉到了尘埃和气体的详细红外特征，以黄色显示。