An exploding white dwarf star blasted itself out of its orbit with another star in a ‘partial supernova’ and is now hurtling across our galaxy, according to a new study from the University of Warwick.

It opens up the possibility of many more survivors of supernovae traveling undiscovered through the Milky Way, as well as other types of supernovae occurring in other galaxies that astronomers have never seen before.

Reported today (July 15, 2020) in Monthly Notices of the Royal Astronomical Society the research, funded by the Leverhulme Trust and Science and Technology Facilities Council (STFC), analyzed a white dwarf that was previously found to have an unusual atmospheric composition. It reveals that the star was most likely a binary star that survived its supernova explosion, which sent it and its companion flying through the Milky Way in opposite directions.

White dwarfs are the remaining cores of red giants after these huge stars have died and shed their outer layers, cooling over the course of billions of years. The majority of white dwarfs have atmospheres composed almost entirely of hydrogen or helium, with occasional evidence of carbon or oxygen dredged up from the star’s core.

This star, designated SDSS J1240+6710 and discovered in 2015, seemed to contain neither hydrogen nor helium, composed instead of an unusual mix of oxygen, neon, magnesium, and silicon. Using the Hubble Space Telescope, the scientists also identified carbon, sodium, and aluminum in the star’s atmosphere, all of which are produced in the first thermonuclear reactions of a supernova.

However, there is a clear absence of what is known as the ‘iron group’ of elements, iron, nickel, chromium, and manganese. These heavier elements are normally cooked up from the lighter ones, and make up the defining features of thermonuclear supernovae. The lack of iron group elements in SDSSJ1240+6710 suggests that the star only went through a partial supernova before the nuclear burning died out.