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Radio signals reveal origin of a supernova

May 17, 2023 | Press release

Artist impression of the double star system with a compact white dwarf star accreting matter from a helium-rich donor companion, surrounded by dense and dusty circumstellar material. It was the interaction of the exploded star and the material left over from this companion that gave rise to the strong radio signal and the conspicuous helium lines in the optical spectra of SN 2020eyj. (Image credit: Adam Makarenko/W. M. Keck Observatory)

Based on original press release by the University of Stockholm.

Astronomers from the Zwicky Transient Facility collaboration based at the University of Stockholm, Sweden have uncovered the origin of a thermonuclear supernova explosion. Strong emission lines of helium and the first detection of such a supernova in radio waves show that the exploding white dwarf star had a helium-rich companion. The results are published in today's issue of the journal Nature.

Supernovae of Type Ia are important for astronomers since they are used to measure the expansion of the Universe. However, the origin of these explosions has remained an open question. While it is established that the explosion is that of a compact white dwarf star somehow accreting too much matter from a companion star, the exact process and the nature of the progenitor is not known. The new discovery of supernova SN 2020eyj established that the companion star was a helium star that had lost much of its material just prior to the explosion of the white dwarf.

“Once we saw the signatures of strong interaction with the material from the companion we tried to also detect it in radio emission”, explains Erik Kool, post-doc at the Department of Astronomy at Stockholm university and lead author of the paper. “The detection in radio is the first one of a Type Ia supernova – something astronomers have tried to do for decades.”

Supernova 2020eyj was discovered by the Zwicky Transient Facility camera on Palomar mountain, where the Oskar Klein Centre at Stockholm University are members. – “The Nordic Optical telescope on La Palma was fundamental for following up this supernova”, says Professor Jesper Sollerman at the Department of Astronomy and co-author of the paper. “As were spectra from the large Keck telescope on Hawai’i that immediately revealed the very unusual helium-dominated material around the exploded star.”

“This is clearly a very unusual Type Ia supernova, but still related to the ones we use to measure the expansion of the universe”, adds Joel Johansson from the Department of Physics. “While normal Type Ia supernovae appear to always explode with the same brightness, this supernova tells us that there are many different pathways to a white dwarf star explosion”, he adds.

More Information

This press release is based on the publication "A radio-detected Type la supernova with helium-rich circumstellar material " published in Nature on May 17, 2023. This work is led by Erik Kool from the Department of Astronomy at Stockholm University and describes the first radio detection of a Type Ia supernova. Co-authors from Stockholm University are Joel Johansson, Jesper Sollerman, Steve Schulze, Peter Lundqvist, Sheng Yang, and Conor Omand. This work involved researchers from institutes across the world, including Caltech, Weizmann Institute, IAA-CSIC, NAOJ, Macquarie University, and Trinity College Dublin


Science Contact
Erik Kool
Postdoctoral Fellow (University of Stockholm, Sweden)
erik.kool [at] astro [dot] su [dot] se


An animation showing the SN2020eyj with its compact white dwarf and helium-rich companion star. Credit: Adam Makarenko/W. M. Keck Observatory