First radio signal reveals supernova origin

Posted on: 17 May 2023

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. Credit: Adam Makarenko/W. M. Keck Observatory.

Supernovae of Type Ia are important for astronomers since they are used to measure the expansion rate of the Universe and were instrumental in the discovery of dark energy – a discovery that was awarded the Nobel Prize in Physics in 2011. However, the origin of these explosions has remained a key mystery in astronomy.  

Type Ia supernovae also offer insights into the formation of heavy elements such as iron and how this newly formed material is ejected at high velocities out into the Universe and is used to form the next generations of stars and planets.

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 system 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.

“This stellar explosion is very exciting because it is the very first time that radio waves have been detected from the explosion of a white dwarf,” explains Professor Kate Maguire, an associate professor in astrophysics at Trinity College Dublin, who was involved in the data collection and interpretation of the event.

“This helped us to determine that the companion star was a helium star that shed a lot of its mass very soon before it exploded.”

Supernova 2020eyj was discovered by a leading sky survey, the Zwicky Transient Facility camera on the Palomar Mountain in California, of which the astrophysics group at Trinity is a member. Prof. Maguire and her group at Trinity investigate some of the most powerful explosions in the Universe.

“As soon as it was discovered by the Zwicky Transient Facility it was obvious that this was a very unusual explosion. The observations showed strong signatures of helium matter that are not normally seen in a white dwarf supernova and this different signature suggests that there are likely multiple ways for a white dwarf star to explode,” she added.

The paper, A radio-detected Type Ia supernova with helium-rich circumstellar material, is published today in leading international journal Nature and is led by Erik Kool from the Department of Astronomy at Stockholm University.

Prof. Maguire and her group from the School of Physics at Trinity were involved in this work along with other researchers from institutes across the world, including Caltech, Weizmann Institute, IAA-CSIC, NAOJ, and Macquarie University.

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