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Megapixels: NASA snapped a shot of a holiday 'wreath' in space

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This season is full of stories about stars guiding travelers to far-off destinations, but imagery from NASA's archive shows off a stellar guide of a different sort. The central point of this holiday "wreath" is a bright star known as RS Puppis, or RS Pup for short. RS Pup is what's called a Cepheid variable: a star that periodically dims and gets brighter. The change in luminosity is due to instability—these are large, short-lived stars that are already nearing the end of their chemical fuel reserves, and don't maintain steady transfers of temperature from layer to layer. Astrophysicists can use the variability of these stars' light to calculate how far away they are (6,500 light-years, in this case), allowing them to serve as a sort of cosmic yardstick.



RS Pup cycles through one of these pulsations every 41.5 days, with a rapid rise in brightness followed by a much slower descent back into its dimmest state. It's 200 times larger than our sun and 10 times as massive, with an average brightness 15,000 times greater than our modest host star.



The so-called wreath portion of the image is actually a nebula surrounding RS Pup; a region of interstellar space rich with gas and cosmic dust. This nebula is made to look particularly striking by RS Pup's bouncing luminosity, which means that different clouds of dust in the nebula reflect bursts of bright light at different times. Check out a time-lapse video of the effect, which is known as a light echo:




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Written By Rachel Feltman

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