A never-before-seen 'partial supernova' sent this star's corpse skidding across the galaxy

By Brandon Specktor - Senior Writer 6 hours ago

The runaway star is traveling at nearly 600,000 mph and lost most of its mass to a mysterious explosion.



A white dwarf corpse blasting out of a supernova
(Image: © University of Warwick/Mark Garlick)

An intimate pair of distant stars had a violent falling-out, sending both careening millions of miles a day toward opposite ends of the universe. Relationships, huh?

In 2015, astronomers discovered one of those stars (named SDSS J1240+6710) cruising across the Milky Way. The star's brightness and composition suggested it was a white dwarf — the decaying, Earth-sized husk of a once-enormous red giant. But something about the runaway star's atmosphere seemed off. Typical white dwarfs have outer atmospheres made almost entirely of hydrogen and helium; this star's atmosphere didn't have any of either element.

This atmospheric anomaly prompted researchers to take a closer look at the star — and the story only got weirder. According to the researchers, who detailed their results July 15 in the journal Monthly Notices of the Royal Astronomical Society, the runaway dwarf's size, speed and composition all point to a thermonuclear supernova explosion in its recent past that sent the star and its former binary partner (most explosion-prone white dwarfs are bound to a larger star) blasting out of orbit.

However, the star's atmosphere still lacks several key elements that define these types of explosions. If a supernova knocked SDSS J1240+6710 into interstellar space, it must be a type of supernova "that we haven't seen before," lead study author Boris Gänsicke, an astrophysicist at the University of Warwick in England, said in a statement.

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