The first radio detection of a type Ia supernova sheds light, after decades of debate, on the origin of these explosions

Type Ia supernovae are produced when a white dwarf, the "corpse" of a Sun-like star, absorbs material from a companion star and reaches a critical mass, equivalent to 1.4 solar masses, triggering an explosion whose luminosity will, given its origin, be similar in almost all cases. This uniformity made Type Ia supernovae the ideal objects for measuring distances in the Universe, but the origin and nature of the progenitor system was unknown. Now, the first radio observation of a type Ia supernova confirms that it comes from a double star system consisting of a white dwarf and a solar-type star. The results are published in the journal Nature.

"When we saw signs of a strong interaction with the companion star material in supernova SN2020eyj, we tried to observe the explosion in radio, something that had been attempted without success for decades", explains Erik Kool, a researcher at Stockholm University and lead author of the paper.

Type Ia supernovae always contain a white dwarf, which receives material from its companion. However, it was not known whether this companion was a white dwarf or a Sun-like star, something that radio imaging could reveal.

“This first radio detection of a type Ia supernova is a milestone that has allowed us to demonstrate that the exploded white dwarf was accompanied by a normal, non-degenerate star before the explosion", says Javier Moldón, a researcher at the IAA-CSIC who participated in the discovery. In addition, with these observations we can estimate the mass and geometry of the material surrounding the supernova, which allows us to better understand what the system was like before the explosion.

This work, whose contribution in radio data was led by the IAA-CSIC, has confirmed that the material expelled in the supernova explosion collided, after travelling sixty days, with the material surrounding the system, composed mostly of helium, which indicates that the companion star was not a white dwarf. Furthermore, models predicted that the radio emission, if present, would take many months to be detectable, and indeed the science team had to wait a year and a half to detect the supernova's radio counterpart.

“The unusual light curve of SN 2020eyj, the infrared emission, the detection of helium emission lines and the unprecedented radio detection make this supernova unique, a treasure of information with implications for multiple fields of research", says Miguel Pérez Torres, an IAA-CSIC researcher participating in the study. “Studying more similar systems will allow us to better understand the origin of these standard candles and the chemical evolution of galaxies”.

"Now that we have shown that radio observations can provide direct and unique information to understand this type of supernovae, it opens a path to study these systems with the new generation of radio instruments, such as the Square Kilometre Array Observatory (SKAO) in the future", concludes Javier Moldón (IAA-CSIC).

The result has been possible thanks to e-MERLIN, an array of very high angular resolution radio telescopes, and the analysis of the data has been carried out from the Spanish prototype of the SKA Regional Centre (SPSRC) of the IAA-CSIC, which is supported by the Severo Ochoa project of the IAA and which facilitates the processing of data from SKAO pathfinders, such as e-MERLIN.