More than 1,800 years ago, in the year 185, Chinese astronomers recorded what they called a “guest star” after a bright new light appeared in the night sky. This brightness resulted when a star exploded some 8,000 light-years away, between the constellations of Circinus and Centaurus, into a supernova; the bright event was visible for eight months before fading from view to the naked eye.
Now, all that remains is a ring of debris called RCW 86.
A new image was taken recently of these remnants using the Dark Energy Camera mounted on the Víctor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory in northern Chile.
Wispy strands mark the glowing remains of the supernova, appearing to float like clouds away from the ancient explosion. The rest of the wide field image is filled with stars. The new image is helping astronomers understand how supernovas evolve.
But researchers didn’t always know that SN 185 and RCW 86 were the same thing.
Initially, astronomers believed that when a massive star explodes in a supernova, it would take about 10,000 years for the remnants of that explosion to form a ring-like structure such as the one visible in the Dark Energy Camera’s new image.
But researchers now suspect this supernova experienced an extremely high expansion velocity, meaning the ring structure could form in as little as about 2,000 years after its explosion.
Further research, in the form of X-ray data, revealed large amounts of iron around the region of RCW 86, indicating this supernova was a different type of stellar explosion that occurs within a pair of stars called a binary star system. That explosion has been dubbed a “Type la” supernova
This finding paints a new portrait of what happened in 185: A dense white dwarf star pulled material away from a companion star — and when the star couldn’t support the influx of material from its companion, the white dwarf exploded.
At the same time, high-velocity winds had created a cavity around the white dwarf. This cavity provided enough room for the supernova’s remnants to expand quickly and create the wispy strands seen in the new image.
Given that Type la supernovae are the brightest of all stellar explosions, this ephemeral addition to the night sky likely awed astronomers in 185.