A team of observers using NASA’s Chandra X-ray Observatory has mapped an arc of X-ray emission in the remnant of the supernova observed by Tycho Brahe in 1572. Researchers attribute the pattern of emission to a shock wave created when a white dwarf exploded and blew material off the surface of a nearby companion star. Remarkably, the companion star appears little affected by the blast.
This supports the model of Type 1a supernova formation by accretion of material by a white dwarf from a companion star, followed by explosion. The alternative, that two white dwarfs merge in the supernova explosion, would leave no trace of any companion star, not even the material blown off.
Other details of the arc support the idea that it was blasted from the companion star. For example, the X-ray emission of the remnant shows a “shadow” next to the arc, consistent with the blocking of debris from the explosion by the expanding cone of material stripped from the companion.
Previous studies with optical telescopes have revealed a star within the remnant that is moving much more quickly than its neighbours, hinting that it could be the missing companion. Combining the properties of the X-ray arc and the putative stellar companion, the team determined the orbital period and separation of the two stars in the binary system before the explosion. The period was estimated to be about five days, and the separation about a millionth of a light-year, less than 0.1 AU. The remnant itself is about 20 light-years across.
The supernova explosion seems to have blasted very little material off the companion star. The discovery provides strong evidence that a star can survive the explosive impact generated when its companion goes supernova.
The results appeared in the 1 May issue of The Astrophysical Journal, with lead authors F Lu (Institute of High Energy Physics, Chinese Academy of Sciences, Beijing), and Q D Wang (University of Massachusetts, Amherst, USA).