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.


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