When this gas slams into the existing interstellar medium , it heats up so much it glows in X-rays . Non-uniformity of the interstellar medium causes Vela's appearance to be irregular. The supernova that created this nebula occurred about 1500 light years away and about 11,000 years ago. It is visible as the bright patch near the upper right. This Puppis supernova remnant nebula is actually about four times further than the Vela nebula.
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