Supernova (SN) 185 occurred in 185 CE in the direction of Alpha Centauri, between the constellations of Circinus and Centaurus, and remained visible to the naked eye for about eight months before fading from view. This supernova event was observed by ancient Chinese astronomers in the Book of Later Han and might have been recorded in Roman literature. SN 185 is believed to be the first supernova for which records exist.
RCW 86, the tattered shell of SN 185, was captured by the Dark Energy Camera, which is mounted on the National Science Foundation’s (NSF) Víctor M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF’s NOIRLab. Image credit: CTIO / NOIRLab / DOE / NSF / AURA / T.A. Rector, University of Alaska Anchorage & NSF’s NOIRLab / J. Miller, Gemini Observatory & NSF’s NOIRLab / M. Zamani & D. de Martin, NSF’s NOIRLab.
SN 185 occurred more than 8,000 light-years away in the approximate direction of Alpha Centauri, between the constellations of Circinus and Centaurus.
The resulting structure, known as RCW 86, helps shed light on how the remains of the supernova evolved over the past 1,800 years.
The amazing wide-field vision of the Dark Energy Camera (DECam), which is mounted on the Víctor M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory, enabled astronomers to create a high-resolution image of the entire supernova remnant as it is seen today.
Though the link between RCW 86 and SN 185 is now well established, that wasn’t always the case.
For decades, astronomers thought it would take about 10,000 years for a traditional core-collapse supernova — one in which a massive star blows material away from itself by exploding — to form the structure as we see it today.
This would make the structure far older than the supernova observed in the year 185.
This preliminary estimate largely came from measurements of the supernova remnant’s size.
But in 2006, astronomers found that the large size was due instead to an extremely high expansion velocity.
The new estimate is much more in line with a comparatively youthful age of about 2,000 years, which strengthened the link between RCW 86 and the guest star observed centuries ago.
While a more accurate age estimate brought astronomers one step closer to understanding this unique stellar feature, one mystery still remained.
How did RCW 86 expand so fast? The answer was uncovered when X-ray data of the region revealed large amounts of iron present, a tell-tale sign of a different kind of explosion: a Type Ia supernova.
This type of blast occurs in a binary star system when a dense white dwarf siphons material from its companion star to the point of detonation.
These supernovae are the brightest of all and no doubt SN 185 would have awed observers while it shone brightly in the night sky.
Astronomers now have a more complete picture of how RCW 86 formed.
As the white dwarf of the binary system swallowed the material of its companion star, its high-velocity winds pushed the surrounding gas and dust outward, creating the cavity we observe today.
Then, when the white dwarf could not support any more mass falling onto it from the companion star, it exploded in a violent eruption.
The previously formed cavity gave ample room for the high-velocity stellar remnants to expand very quickly and to create the monumental features we see today.
This new image of RCW 86 gives astronomers an even deeper look into the physics of this perplexing structure and its formation.
