First detection of radio waves of a Type Ia Supernova

Astronomers at Stockholm University have discovered an unusual Type Ia supernova. For the first time, it was detected in radio waves and showed strong emissions of helium. The supernova was triggered by a[{” attribute=””>white dwarf star that pulled helium-rich material from a companion star. This novel finding adds to our understanding of Type Ia supernovae, which are pivotal for measuring the universe’s expansion.

A team of astronomers led by Stockholm University has discovered an unusual Type Ia supernova – or thermonuclear supernova – called SN 2020eyj. Not only did they make the first detection of such a supernova in radio waves, follow-up observations from W. M. Keck Observatory on Maunakea, Hawaiʻi Island also showed strong emission lines of helium.

This marks the first confirmed Type Ia supernova triggered by a white dwarf star that pulled material from a companion star with an outer layer consisting primarily of helium; normally, in the rare cases where the material stripped from the outer layers of the donor star could be detected in spectra, this was mostly hydrogen.

Type Ia supernovae 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 caused by a compact white dwarf star that somehow accretes 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 is evidence the companion star was a helium star that had lost much of its material just prior to the explosion of the white dwarf.

The study, which includes data from Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS), is published in the May 17th issue of the journal Nature.

An artist’s impression of a double star system with a compact white dwarf star accreting material from a helium-rich donor companion, surrounded by dense, dusty material. It was the interaction between the exploding star and the remnant material of this companion that gave rise to the strong radio signal and clear helium lines in the optical spectra of SN 2020eyj. Credit: Adam Makarenko Observatory/WM Keck

“Once we saw the signatures of the strong interaction with the companion material, we also tried to detect it in the radio emissions,” says Erik Kohl, a postdoctoral researcher 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 been trying to do for decades.”

The 2020eyj supernova was first observed by the Zwicky Transit Facility at the Palomar Observatory near San Diego where the Oskar Klein Center at Stockholm University are members.

“The Northern Optical Telescope at La Palma was key to following this supernova,” says Jesper Sollerman, professor in the Department of Astronomy at Stockholm University 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 is still related to the ones we use to measure the expansion of the universe,” adds co-author Joel Johansson from Stockholm University’s Department of Physics. “While a normal type Ia supernova always seems to explode with the same brightness, this supernova tells us that there are many different pathways for a white dwarf star to explode.”

For more information on this research, see Radio Signal Reveals Origin of Thermonuclear Supernova Explosion.

Reference: “Radio-detected Type Ia Supernova with Helium-Rich Material” by Erik C. Kool, Joel Johansson, Jesper Sollerman, Javier Moldón, Takashi J. Moriya, Seppo Mattila, Steve Schulze, Laura Chomiuk, and Miguel Pérez-Torres, Available here. Chelsea Harris, Peter Lundqvist, Matthew Graham, Sheng Yang, Daniel A. Burley, Nora-Lynn Strutjohan, Christopher Fremling, Avishai Gal-Yam, Jeremy Lesmi, Kate Maguire, Connor Omand, Matthew Smith, Igor Andreoni, Eric C. Bellem, Joshua S. Bloom, Keshalai D, Stephen L Groome, Mansi M Kasliwal, Frank J Massey, Michael S Medford, Sungmin Park, Josiah Purdum, Thomas M Reynolds, Red Riddell, Estelle Robert, Stuart D Rider, Yashvi Sharma & Daniel Stern May 17, 2023, Available here. nature.
doi: 10.1038/s41586-023-05916-w