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The Necklace Nebula — which also goes by the less glamorous name of PN G054.2-03.4 — was produced by a pair of tightly orbiting Sun-like stars. Roughly 10000 years ago, one of the aging stars expanded and engulfed its smaller companion, creating something astronomers call a “common envelope”. The smaller star continued to orbit inside its larger companion, increasing the bloated giant’s rotation rate until large parts of it spun outwards into space. This escaping ring of debris formed the Necklace Nebula, with particularly dense clumps of gas forming the bright “diamonds” around the ring.
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This work is based on NASA’s Chandra X-ray Observatory observations of the remains of a supernova called Cassiopeia A, located in our galaxy ~ 11k ly from Earth.
This is one of the youngest known supernova remnants, with an age of about 350 years.
When the supernova happened, titanium fragments were produced deep inside the massive star. The fragments penetrated the surface of the massive star, forming the rim of the supernova remnant, Cas A. The amount of stable titanium produced in Cas A exceeds the total mass of the Earth.