Free Astronomy Magazine May-June 2023

41 MAY-JUNE 2023 ASTRO PUBLISHING This preliminary estimate largely came from measurements of the su- pernova remnant’s size. But, a 2006 study found that the large size was due instead to an extremely high ex- pansion velocity. The new estimate is much more in line with a compar- atively youthful age of about 2000 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 (the end- of-life remains of a star like our Sun) 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 com- plete picture of how RCW 86 formed. As the white dwarf of the binary system swallowed the mate- rial of its companion star, its high-ve- locity 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 perplex- ing structure and its formation. The image was obtained by NOIRLab’s Communication, Education & En- gagement team as part of the NOIR- Lab Legacy Imaging Program. T he tattered shell of the first-ever recorded supernova was cap- tured by the US Department of En- ergy-fabricated Dark Energy Camera, which is mounted on the National Science Foundation’s (NSF) Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF’s NOIR- Lab. A ring of glowing debris is all that remains of a white dwarf star that exploded more than 1800 years ago when it was recorded by Chi- nese astronomers as a ‘guest star’. This special image, which covers an impressive 45 arcminutes on the sky, gives a rare view of the entirety of this supernova remnant. [CTIO/NOIR- Lab/DOE/NSF/AURA. T.A. Rector (Uni- versity of Alaska Anchorage/NSF’s NOIRLab), J. Miller (Gemini Observa- tory/NSF’s NOIRLab), M. Zamani & D. de Martin (NSF’s NOIRLab)] R CW 86’s ring of debris is all that remains of a white-dwarf star that exploded more than 1800 years ago, when it was recorded by Chinese stargazers as a ‘guest star’. This video presents the new image of the supernova remnant. [Im- ages and Videos: TIO/NOIRLab/DOE/NSF/AURA, T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), J. Miller (Gemini Observatory/NSF’s NOIRLab), M. Za- mani & D. de Martin (NSF’s NOIRLab), ESA/Hubble/L. Calcada, D. Munizaga, N. Bartmann. Music: Stellardrone - In Time] light-years away in the approximate direction of Alpha Centauri, be- tween the constellations of Circinus and Centaurus. The resulting struc- ture, RCW 86 — as imaged by the Dark Energy Camera (DECam) mounted on the Víctor M. Blanco 4- meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF’s NOIRLab — helps shed light on how the re- mains of the supernova evolved over the past 1800 years. DECam’s amazing wide-field vision enabled astronomers to create this rare view 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 explod- ing — to form the structure as we see it today. This would make the structure far older than the super- nova observed in the year 185. !