In the latest issue of the magazine nature, Astronomers from Stockholm University reveal the origin of a thermonuclear supernova explosion. Strong helium emission lines and the first detection of such a supernova in radio waves show that the exploding white dwarf star had a helium-rich companion.
Type Ia supernovae are important to astronomers because they are used to measure the expansion of the universe. However, the source of these eruptions remained an open question. While the explosion has been shown to be an explosion of a compact white dwarf star that somehow accumulated a lot of matter from a companion star, the exact process and nature of the progenitor are unknown. The new discovery of the supernova SN 2020eyj proves that the companion star was a helium star that lost much of its matter before the white dwarf exploded.
“Once we saw the signatures of the strong interaction with the companion material, we also tried to detect it in the radio emissions,” explains Erik Kohl, a postdoctoral fellow in the Department of Astronomy at Stockholm University and lead author of the paper. “The detection in radio is the first of a type Ia supernova — something astronomers have tried to do for decades.”
Supernova 2020eyj was discovered by the Zwicky Transient Facility’s camera on Mount Palomar, where the Oskar Klein Center at Stockholm University has members.
“The Northern Optical Telescope at La Palma was key to following this supernova,” says Professor Jesper Sollermann of the Department of Astronomy and co-author of the paper. “As were the spectra from the Large Keck Telescope in Hawaii which immediately revealed a very unusual helium-dominated material around the exploding star.”
“This is clearly an unusual Type Ia supernova, but it’s still related to the ones we use to measure the expansion of the universe,” adds Joel Johansson of the Department of Physics.
“While it seems that Type Ia supernovae always explode with the same brightness, this supernova tells us that there are many different pathways for the explosion of a white dwarf star,” he adds.