The electron-capture origin of supernova 2018zd

HIRAMATSU, DAICHI; HOWELL, D. ANDREW; VAN DYK, SCHUYLER D.; GOLDBERG, JARED A.; MAEDA, KEIICHI; MORIYA, TAKASHI J.; TOMINAGA, NOZOMU; NOMOTO, KEN?ICHI; HOSSEINZADEH, GRIFFIN; ARCAVI, IAIR; MCCULLY, CURTIS; BURKE, JAMISON; BOSTROEM, K. AZALEE; VALENTI, STEFANO; DONG, YIZE; BROWN, PETER J.; ANDREWS, JENNIFER E.; BILINSKI, CHRISTOPHER; WILLIAMS, G. GRANT; SMITH, PAUL S.; SMITH, NATHAN; SAND, DAVID J.; ANAND, GAGANDEEP S.; XU, CHENGYUAN; FILIPPENKO, ALEXEI V.; BERSTEN, MELINA C.; FOLATELLI, GASTÓN; KELLY, PATRICK L.; NOGUCHI, TOSHIHIDE; ITAGAKI, KOICHI

Nature Astronomy

Nature Research

Año: 2021 vol. 5 p. 903 - 910

In the transitional mass range (~8–10 solar masses) between white dwarf formation and iron core-collapse supernovae, stars are expected to produce an electron-capture supernova. Theoretically, these progenitors are thought to be super-asymptotic giant branch stars with a degenerate O + Ne + Mg core, and electron capture onto Ne and Mg nuclei should initiate core collapse1–4. However, no supernovae have unequivocally been identified from an electron-capture origin, partly because of uncertainty in theoretical predictions. Here we present six indicators of electron-capture supernovae and show that supernova 2018zd is the only known supernova with strong evidence for or consistent with all six: progenitor identification, circumstellar material, chemical composition5–7, explosion energy, light curve and nucleosynthesis8–12. For supernova 2018zd, we infer a super-asymptotic giant branch progenitor based on the faint candidate in the pre-explosion images and the chemically enriched circumstellar material revealed by the early ultraviolet colours and flash spectroscopy. The light-curve morphology and nebular emission lines can be explained by the low explosion energy and neutron-rich nucleosynthesis produced in an electron-capture supernova. This identification provides insights into the complex stellar evolution, supernova physics, cosmic nucleosynthesis and remnant populations in the transitional mass range.