No surviving evolved companions of the progenitor of SN 1006

A search for a surviving companion star of the progenitor of type Ia supernova 1006 indicates that fewer than 20 per cent of such supernovae result from the accretion onto the progenitor star of material from a companion that survives the process rather than being destroyed. White dwarf binary as SN 1006 progenitor Type Ia supernovae are thought to occur in binaries containing a white dwarf and a companion that is a red giant, subgiant, main-sequence star or another white dwarf. In the last of these options, the 'double-degenerate' case, the two white dwarfs would merge before the explosion and no companion would be left. In a single-degenerate system the former companion star would survive. Previous searches for remnant companions have revealed one contested case for the Tycho Brahe supernova SN 1572. More recently, observations have restricted surviving companions to small, main-sequence stars, ruling out giant companions. Jonay González Hernández et al . report the result of a search for surviving companions to the progenitor of SN 1006 and find no sign of a former companion. Together with previous results, this suggests that fewer than 20% of type Ia supernovae occur through the single-degenerate channel, the slow accumulation of mass from a large star. The more common trigger, it seems, is the rapid break-up of a smaller orbiting white dwarf. Type Ia supernovae are thought to occur when a white dwarf made of carbon and oxygen accretes sufficient mass to trigger a thermonuclear explosion 1 . The accretion could be slow, from an unevolved (main-sequence) or evolved (subgiant or giant) star 2 , 3 (the single-degenerate channel), or rapid, as the primary star breaks up a smaller orbiting white dwarf 3 , 4 (the double-degenerate channel). A companion star will survive the explosion only in the single-degenerate channel 5 . Both channels might contribute to the production of type Ia supernovae 6 , 7 , but the relative proportions of their contributions remain a fundamental puzzle in astronomy. Previous searches for remnant companions have revealed one possible case for SN 1572 (refs 8 , 9 ), although that has been questioned 10 . More recently, observations have restricted surviving companions to be small, main-sequence stars 11 , 12 , 13 , ruling out giant companions but still allowing the single-degenerate channel. Here we report the results of a search for surviving companions of the progenitor of SN 1006 (ref. 14 ). None of the stars within 4 arc minute