A mystery surrounding a supernova seen by Chinese astronomers in AD185, has been solved. RCW 86 lit up the sky for eight months.
In more recent times, astronomers have wondered how it grew so large, so fast.
The BBC reports that space telescope observations now suggest that before exploding, a wind of material from the star blew a cavity around it, into which the supernova could expand much more quickly.
The supernova is about 8000 light-years away, but is huge. If the infrared light it emits could be seen by our eyes, it would appear to be as large in the sky as the full Moon.
Findings published in the Astrophysical Journal combine existing data from the Chandra X-ray telescope and the XMM-Newton Observatory with recent images from NASA's Spitzer and Wide-field Infrared Survey telescopes.