An intimate pair of distant stars had a violent fall, sending the two million miles a day to opposite ends of the universe. Relationships, huh?
In 2015, astronomers discovered one of those stars (called SDSS J1240 + 6710) crossing the Milky Way. The star’s brightness and composition suggested it was a white dwarf – the decaying, Earth-sized shell of a once-giant red giant. But something about the fugitive star’s atmosphere seemed out of place. Typical white dwarfs have external atmospheres made almost entirely of hydrogen and helium; The atmosphere of this star had none of the elements.
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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 on July 15 in the journal Monthly notices from the Royal Astronomical Society, size, speed and composition of the runaway dwarf point to a thermonuclear supernova Explosion in its recent past that sent the star and its former binary companion (most explosion-prone white dwarfs linked to a larger star) leaving orbit.
However, the star’s atmosphere still lacks several key elements that define such explosions. If a supernova launched SDSS J1240 + 6710 into interstellar space, it must be a type of supernova “we haven’t seen before”, the study’s lead author, Boris Gänsicke, an astrophysicist at the University of Warwick in England, he said in a statement.
In their new study, Gänsicke and colleagues investigated observations of the star from NASA’s Hubble Space Telescope and the European Space Agency’s Gaia satellite. Gaia’s data revealed that SDSS J1240 + 6710 is traversing the galaxy at approximately 560,000 mph (900,000 km / h), and has a mass of approximately 40% of Earth Sun. That’s high speed and low mass for a typical white dwarf, the researchers wrote, suggesting that the star may have lost some of its mass due to a huge explosion.
Certain elements in the dwarf’s atmosphere also pointed to a supernova. The star’s atmosphere contained abundant sodium, carbon, oxygen, and aluminum, all elements produced during the first phase of a thermonuclear supernova, when the star’s fiery energy fuses lighter elements into heavier elements, the team wrote. In the most common types of supernovae, the fusion process usually culminates in the creation of heavy elements like iron, nickel, and chromium, but the researchers were unable to detect any of those heavy metals in the atmosphere of a strange dwarf.
What does this all mean? It is almost as if SDSS J1240 + 6710 began to explode in a thermonuclear supernova, and suddenly stopped in the middle. The explosion appears to have been strong enough to blow up the star’s lightest and outermost layers of gas and knock the star and its former partner out of orbit; however, something halted the nuclear fusion process before heavy elements were forged, Gänsicke said.
While this theory explains the below-average star mass and bizarre atmospheric composition, a “partial” supernova like this has never before been observed in the universe. It would also be very difficult for astronomers to “catch one in the act” of the explosion, Gänsicke said, since most supernovae are detected by the radioactive glow of their nickel (one of the heavy elements that this nickel lacks. runaway dwarf). Still, the existence of the strange dwarf serves as another reminder that there are many inexplicable phenomena that revolve around the death cycles of stars.
“We are now discovering that there are different types of white dwarfs that survive supernovae in different conditions … clearly there is a complete zoo,” said Gänsicke.