Unique portrait of a supernova that exploded more than 1,800 years ago

Credit: National Science Foundation

The RCW 86 debris ring, a remnant of the first supernova recorded in history more than 1,800 years ago by Chinese astronomers, has been photographed by a telescope in Chile.

The Dark Energy Camera (DECam), installed in the Víctor M. Blanco 4-meter Telescope of the NSF (National Science Foundation) at the Cerro Tololo Inter-American Observatory, captured the unique portrait of what remains of a white dwarf star whose explosion was produced in the year 185 of our era.

Around the outer edges of this star-studded image are fuzzy filaments that appear to be moving away from a central point, like the remains of a burst balloon.

When the supernova appeared in the sky, ancient astronomers called this puzzling phenomenon in the night sky a “guest star,” which could be seen with the naked eye in the sky for about eight months before disappearing.

This historic supernova, now referred to by astronomers as 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, RCW 86, helps shed light on how the supernova remnants evolved over the past 1,800 years. DECam’s wide-field view allowed astronomers to create this unusual perspective of the entire supernova remnant as it appears today, the NSF reports in a statement.

Although the link between RCW 86 and SN 185 is now well established, it was not always so. For decades, astronomers thought that a traditional core-collapsing supernova—in which a massive star explodes material from itself—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 AD 185.

This preliminary estimate was based primarily on measurements of the size of the supernova remnant. However, a study in 2006 found that its large size was due to an extremely high rate of expansion. The new estimate is much closer to a comparatively younger age of about 2,000 years, reinforcing the link between RCW 86 and the guest star observed centuries ago.

While a more accurate estimate of the age of this cosmic phenomenon brought astronomers closer to understanding this unique stellar event, a mystery still remained to be solved. 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 telltale 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 star (the end-of-life remnants of a star like our Sun) diverts material from its companion star to the detonation point. These supernovae are the brightest of all, and SN 185 would no doubt have wowed observers as it shimmered in the night sky.

Astronomers now have a more complete idea of how RCW 86 formed. When the white dwarf in the binary system swallowed material from its companion star, its high-velocity winds pushed surrounding gas and dust outward, creating the cavity. what we see today.