The final fate of massive stars depends on many factors. Theory suggests that some with initial masses greater than 25 to 30 solar masses end up as Wolf–Rayet stars, which are deficient in hydrogen in their outer layers because of mass loss through strong stellar winds. The most massive of these stars have cores which may form a black hole and theory predicts that the resulting explosion of some of them produces ejecta of low kinetic energy, a faint optical luminosity and a small mass fraction of radioactive nickel1,2,3. An alternative origin for low-energy supernovae is the collapse of the oxygen–neon core of a star of 7–9 solar masses4,5. No weak, hydrogen-deficient, core-collapse supernovae have hitherto been seen. Here we report that SN 2008ha is a faint hydrogen-poor supernova. We propose that other similar events have been observed but have been misclassified as peculiar thermonuclear supernovae (sometimes labelled SN 2002cx-like events6). This discovery could link these faint supernovae to some long-duration γ-ray bursts, because extremely faint, hydrogen-stripped core-collapse supernovae have been proposed to produce such long γ-ray bursts, the afterglows of which do not show evidence of associated supernovae7,8,9.
This work, conducted as part of the European Science Foundation EURYI Awards scheme, was supported by funds from the Participating Organisations of EURYI and the EC Sixth Framework Programme. The work of S.B., E.C. and M.T. was supported by grants of the PRIN of Italian Ministry of University and Science Research. This paper is based on observations collected at TNG, NOT, LT (La Palma Canary Island, Spain), at Ekar (Asiago Observatory, Italy), at the Begues Observatory and Arguines Observatory telescopes (Barcelona and Segorbe, Spain), at the Taurus Hill Observatory (Varkaus, Finland), at the Calar Alto Observatory (Spain) and at the ESO-UT2 (Paranal, Chile). Our analysis included data from the SUSPECT Archive (http://bruford.nhn.ou.edu/~suspect/index1.html). This manuscript made use of information contained in the Bright Supernova web pages (D. Bishop), as part of the Rochester Academy of Sciences.
This file contains Supplementary Methods and Data, Supplementary Tables 1-2, Supplementary Figures 1-4 with Legends and Supplementary References.