Image credit: Max-Planck-Institut für extraterrestrische Physik (MPE)
The supernova remnant RCW 86 most likely comes from the explosion of a star observed by Chinese astronomers in AD 185. Known previously, this event is the first Galactic supernova from which there exists written records. The X-ray image shows an annular structure enclosing a nearly emission-free region. Although the strong brightening is expected from conventional models developed for the spread of supernova shock waves, it is observed in this clearness only in RCW86. Nevertheless, inhomogeneities in the interstellar medium lead apparently to deviation from an idealized spherical shape and to variations in the brightness along the periphery. This gives it a 'diamond ring' like appearance.
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