The research group of Izumi Hachisu (The University of Tokyo), Mariko Kato (Keio University) and Ken'ichi Nomoto (Kavli IPMU, The University of Tokyo) discovered that a Type Ia supernova occurs after its companion star evolves into a faint helium white dwarf in many cases, given the fact that the white dwarf is spinning in the progenitor system.
Supernovae are brilliant explosions of stars. Among them, Type Ia supernovae have been used as "standard candles", which has led to the discovery of the accelerating expansion of the universe. Type Ia supernovae are also important to study as they are the main producer of iron group elements in the universe. Type Ia supernovae are accepted as thermonuclear explosions of carbon-oxygen white dwarfs in binary star systems. However, the debate still continues over two possible progenitor scenarios: one is that two carbon-oxygen white dwarfs coalesce and then explode (Double Degenerate [DD] scenario), and the other is that a white dwarf, accreting mass from its companion star, increases its mass and then explodes (Single Degenerate [SD] scenario).
Some recent observations have provided indications of the progenitor binary star systems just before the explosions. For example, the observations of the remnant of Kepler's supernova in 1604 and the recent supernova PTF 11kx have shown evidence that the companion star is a red giant.
These observations support the SD scenario. On the other hand, no companion star was found for the Type Ia supernova SN 2011fe in the nearby galaxy M101. In another example, no companion star is seen inside a supernova remnant in the Large Magellanic Cloud. Such observations have been generally considered unfavorable to the SD scenario but favorable to the DD scenario.
Recently, the research group took into account the fact that the white dwarf is spinning in the progenitor system. They found that, in many cases, a Type Ia supernova occurs after the companion star evolves into a helium white dwarf. Such helium white dwarf companions would be so faint as to be unobservable before and after a Type Ia supernova explosion. This new SD scenario explains in a unified manner why no signatures of the companion star are seen in many Type Ia supernovae, whereas some Type Ia supernovae indicate the presence of the companion star.
Yoshihisa Obayashi / Tomomi Hijikata
Associate Professor, The University of Tokyo
Professor, Faculty of Science and Technology, Keio University
Professor and Principal Investigator, Kavli Institute for the Physics and Mathematics of the Universe, [Kavli IPMU], The University of Tokyo
The paper has been published in the September 1, 2012, issue of The Astrophysical Journal Letters, vol. 756, L4 [http://dx.doi.org/10.1088/2041-8205/756/1/L4]. Title: "Final Fates of Rotating White Dwarfs and Their Companions in the Single Degenerate Model of Type I Supernovae." Authors: Izumi Hachisu, Mariko Kato, and Ken'ichi Nomoto.