煤袋星云

This stunning image captures a small region on the edge of the inky Coalsack Nebula, or Caldwell 99. Caldwell 99 is a dark nebula — a dense cloud of interstellar dust that completely blocks out visible wavelengths of light from objects behind it. The object at the center of the image is a (much smaller) protoplanetary nebula. The protoplanetary nebula phase is a late stage in the life of a star in which it has ejected a shell of hydrogen gas and is quickly heating up. This stage only lasts for a few thousand years before the protoplanetary nebula’s central star reaches roughly 30,000 Kelvin (approximately 17,000 degrees Fahrenheit). At this point, the central star is producing enough energy to make its surrounding shell of gas glow, becoming what’s known as a planetary nebula.

这张令人惊叹的照片抓拍到了黑色煤袋星云(又称考德威尔99)边缘的一小块区域。考德威尔99是一个黑暗星云——一团密集的星际尘埃云，它完全挡住了来自它后面物体的可见波长的光。图像中心的物体是一个(小得多的)原行星状星云。原行星状星云阶段是恒星生命的后期阶段，在这一阶段，恒星喷射出一层氢气并迅速升温。这个阶段只持续了几千年，然后原行星状星云的中心恒星达到大约30000开尔文(大约17000华氏度)。此时，中心恒星正在产生足够的能量使其周围的气层发光，形成所谓的行星状星云。