Supernova SN 185 exploded in 185 AD in the direction of Alpha Centauri, between the constellations Circulus and Centaurus, and remained visible to the naked eye for about eight months before disappearing from view. This extraordinary event was observed by ancient Chinese as well as Roman astronomers and was recorded in the literature. SN 185 is believed to be the first supernova for which records exist.
The explosion occurred at a distance of more than 8000 light years. The resulting structure, known as RCW 86, helps shed light on how supernova remnants have evolved over the past 1,800 years.
The amazing wide-angle image of the Dark Energy Camera (DECam) mounted on the 4-meter Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory has allowed astronomers to create a high-resolution image of the entire supernova remnant.
While communications between RCW 86 and SN 185 are now well established, this was not always the case.
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For decades, astronomers thought that a traditional core collapse supernova, in which a massive star ejects material from itself in an explosion, would take about 10,000 years to form the structure we see today.
This would make the structure much older than the supernova observed in 185. This preliminary estimate is largely based on measurements of the size of the supernova remnant.
But in 2006, astronomers discovered that the large size is due to the extremely fast expansion rate.
The new estimate is much better at a relatively young age of about 2,000 years, which strengthens the link between RCW 86 and a star observed many centuries ago.
While a more accurate age estimate has brought astronomers one step closer to understanding this unique stellar feature, one mystery still remains.
How did RCW 86 expand so quickly? The answer was discovered when X-ray data from the region revealed the presence of large amounts of iron, a tell-tale sign of another type of explosion: a Type Ia supernova.
This type of explosion occurs in a binary star system when a dense white dwarf siphons material from its companion star and eventually explodes.
These supernovae are the brightest of all, and no doubt SN 185 would leave observers in awe if it shone brightly in the night sky.
Astronomers now have a better idea of how RCW 86 formed.
As the binary’s white dwarf consumed material from its companion star, its high-velocity winds pushed the surrounding gas and dust outward, creating the cavity we see today. Then, when the white dwarf was unable to absorb more of the mass falling on it from its companion star, it exploded.
The previously formed cavity provided enough space for the high-velocity stellar remnants to expand very rapidly and create the monumental features we see today.
This new image of RCW 86 gives astronomers an even deeper look into the physics of this enigmatic structure and its formation.
