Caldwell 15 NGC6826
by Nasa
Title
Caldwell 15 NGC6826
Artist
Nasa
Medium
Photograph - Photograph
Description
NGC 6826 (also known as Caldwell 15) is a planetary nebula located in the constellation Cygnus. It is commonly referred to as the blinking planetary. When viewed through a small telescope, the brightness of the central star overwhelms the eye when viewed directly, obscuring the surrounding nebula. However, it can be viewed well in the peripheral vision (averted vision), which causes it to blink in and out of view as the observer's eye wanders. A distinctive feature of this nebula are the two bright patches on either side, which are known as FLIERs, or Fast Low-Ionization Emission Regions. They appear to be relatively young, moving outwards at supersonic speeds. X-ray emission from Chandra is colored purple and optical emission from the Hubble Space Telescope is colored red, green and blue. A planetary nebula is a phase of stellar evolution that the sun should experience several billion years from now, when it expands to become a red giant and then sheds most of its outer layers, leaving behind a hot core that contracts to form a dense white dwarf star. A wind from the hot core rams into the ejected atmosphere, creating the shell-like filamentary structures seen with optical telescopes. The diffuse X-ray emission is caused by shock waves as the wind collides with the ejected atmosphere. The properties of the X-ray point sources in the center of about half of the planetary nebulas suggest that many central stars responsible for ejecting planetary nebulas have companion stars. Release date October 10, 2012.
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April 16th, 2015
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