Over 250,000 years ago the outer shell of a massive Wolf-Rayet star began to shed its outer atmosphere, creating this beautiful orange nebula of expanding gas as the star gives off the mass of our Sun every 10,000 years.
On the left are two photos I took of this object. The top one is zoomed in a bit, while the bottom wide-angle version shows almost a full 35mm frame. Along the edge of the bottom photograph you can just barely see the much larger emission nebulosity that is over 4700 light years away in the constellation Cygnus.
This planetary nebula is about 1/4 the size of the full-moon, small enough to make it a challenging object to capture at magnitude 10, but larege enough to show some detail on my short focal length telescope.
Here's what the Hubble Space Telescope saw!
This is only a small part of the Crescent Nebula. Use your mouse to explore my photograph (top left) and see if you can find where this Hubble shot was taken. If you need help, move your mouse to the far upper left corner and the location will be identified.
The star WR 136 created this web of luminous material during the late stages of its life. As a bloated, red super-giant, WR 136 gently puffed away some of its bulk, which settled around it. When the star passed from a super-giant to a Wolf-Rayet, it developed a fierce stellar wind - a stream of charged particles released from its surface - and began expelling mass at a furious rate.
The star began ejecting material at a speed of 3.8 million mph (6.1 million kilometers per hour), losing matter equal to that of our Sun's every 10,000 years.
Then the stellar wind collided with the material around the star and swept it up into a thin shell. That shell broke apart into the network of bright clumps seen in the image.
The present-day strong wind of the Wolf-Rayet star has only now caught up with the outer edge of the shell, and is stripping away matter as it flows past [the tongue-shaped material in the upper right of the Hubble image].
The stellar wind continues moving outside the shell, slamming into more material and creating a shock wave. This powerful force produces an extremely hot, glowing skin [seen in blue], which envelops the bright nebula. A shock wave is analogous to the sonic boom produced by a jet plane that exceeds the speed of sound; in a cosmic setting, this boom is seen rather than heard. The outer material is too thin to see in the image until the shock wave hits it. The cosmic collision and subsequent shock wave implies that a large amount of matter resides outside the visible shell. The discovery of this material may explain the discrepancy between the mass of the entire shell (four solar masses) and the amount of matter the star lost when it was a red super-giant (15 solar masses).
The nebula's short-term fate is less spectacular. As the stellar wind muscles past the clumps of material, the pressure around them drops. A decrease in pressure means that the clumps expand, leading to a steady decline in brightness and fading perhaps to invisibility.
Later, the shell may be compressed and begin glowing again, this time as the powerful blast wave of the Wolf-Rayet star completely destroys itself in a powerful supernova explosion.
Crescent Nebula NGC6888
